1
|
Low-Temperature Chiral Crystal Structure and Superconductivity in (Pt 0.2Ir 0.8) 3Zr 5. J Am Chem Soc 2024; 146:773-781. [PMID: 38148506 DOI: 10.1021/jacs.3c10797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2023]
Abstract
We report the observation of superconductivity in (Pt0.2Ir0.8)3Zr5 with a chiral space group (P6122) at low temperatures. The bulk nature of the superconductivity at a transition temperature of 2.2 K was confirmed using specific heat measurements. We revealed that (Pt0.2Ir0.8)3Zr5 obeys the weak-coupling Bardeen-Cooper-Schrieffer model, and the dominant mechanism in the upper critical field is the orbital pair-breaking limit rather than the Pauli-Clogston limit. This indicates that the antisymmetric spin-orbit coupling caused by the chiral crystal structure does not significantly affect the superconductivity of (Pt0.2Ir0.8)3Zr5.
Collapse
|
2
|
Observation of superconductivity and enhanced upper critical field of η-carbide-type oxide Zr 4Pd 2O. Sci Rep 2023; 13:22458. [PMID: 38105267 PMCID: PMC10725861 DOI: 10.1038/s41598-023-49707-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2023] [Accepted: 12/11/2023] [Indexed: 12/19/2023] Open
Abstract
We report the first observation of bulk superconductivity of a η-carbide-type oxide Zr4Pd2O. The crystal structure and the superconducting properties were studied through synchrotron X-ray diffraction, magnetization, electrical resistivity, and specific heat measurement. The superconducting transition was observed at Tc = 2.73 K. Our measurement revealed that the η-carbide-type oxide superconductor Zr4Pd2O shows an enhanced upper critical field μ0Hc2(0) = 6.72 T, which violates the Pauli-Clogston limit μ0HP = 5.29 T. On the other hand, we found that the enhanced upper critical field is absent in a Rh analogue Zr4Rh2O. The large μ0Hc2(0) of Zr4Pd2O would be raised from strong spin-orbit coupling with Pd-4d electrons. The discovery of new superconducting properties for Zr4Pd2O would shed light on the further development of η-carbide-type oxide superconductors.
Collapse
|
3
|
Creation of a Highly Active Small Cu-Based Catalyst Derived from Copper Aluminium Layered Double Hydroxide Supported on α-Al 2 O 3 for Acceptorless Alcohol Dehydrogenation. Chem Asian J 2023; 18:e202300727. [PMID: 37752095 DOI: 10.1002/asia.202300727] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2023] [Revised: 09/18/2023] [Accepted: 09/25/2023] [Indexed: 09/28/2023]
Abstract
A highly dispersed carbonate-intercalated Cu2+ -Al3+ layered double hydroxide (CuAl LDH) was created on an unreactive α-Al2 O3 surface (CuAl LDH@α-Al2 O3 ) via a simple coprecipitation method of Cu2+ and Al3+ under alkaline conditions in the presence of α-Al2 O3 . A highly reducible CuO nanoparticles was generated, accompanied by the formation of CuAl2 O4 on the surface of α-Al2 O3 (CuAlO@α-Al2 O3 ) after calcination at 1073 K in air, as confirmed by powder X-ray diffraction (XRD) and Cu K-edge X-ray absorption near edge structure (XANES). The structural changes during the progressive heating process were monitored by using in-situ temperature-programmed synchrotron XRD (tp-SXRD). The layered structure of CuAl LDH@α-Al2 O3 completely disappeared at 473 K, and CuO or CuAl2 O4 phases began to appear at 823 K or 1023 K, respectively. Our synthesised CuAlO@α-Al2 O3 catalyst was highly active for the acceptorless dehydrogenation of benzylic, aliphatic, or cyclic aliphatic alcohols; the TON based on the amount of Cu increased to 163 from 3.3 of unsupported CuAlO catalyst in 1-phenylethanol dehydrogenation. The results suggested that Cu0 was obtained from the reduction of CuO in the catalyst matrix during the reaction without separate reduction procedure and acted as a catalytically active species.
Collapse
|
4
|
Topochemical Synthesis of LiCoF 3 with a High-Temperature LiNbO 3-Type Structure. Inorg Chem 2022; 61:11746-11756. [PMID: 35861755 DOI: 10.1021/acs.inorgchem.2c01439] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
A novel perovskite fluoride, LixCoF3, which has an exceptionally low tolerance factor (0.81), has been synthesized via low-temperature lithium intercalation into a distorted ReO3-type fluoride CoF3 using organolithium reagents. Interestingly, this reaction is completed within 15 min at room temperature. Synchrotron X-ray diffractometry and optical second harmonic generation at room temperature have revealed that this compound shows a high-temperature LiNbO3-type structure (space group: R3̅c) involving Li-Co antisite defects and A-site splitting along the c direction. A-site splitting is consistent with the prediction based on hybrid Hartree-Fock density functional theory calculations. Co-L2,3 edge X-ray absorption spectroscopy, as well as bond valence sum analysis, has verified the divalent oxidation state of Co ions in the lithiated phase, suggesting that its composition is close to LiCoF3 (x ≈ 1). This compound exhibits a paramagnetic-to-antiferromagnetic transition at 36 K on cooling, accompanied by weak ferromagnetic ordering. The synthetic route based on low-temperature lithiation of metal fluorides host paves the way for obtaining a new LiNbO3-type fluoride family.
Collapse
|
5
|
Synthesis and Characterization of High-Entropy-Alloy-Type Layered Telluride MBi 2Te 4 ( M = Ag, In, Sn, Pb, Bi). MATERIALS (BASEL, SWITZERLAND) 2022; 15:2614. [PMID: 35407946 PMCID: PMC9000834 DOI: 10.3390/ma15072614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 03/29/2022] [Accepted: 03/30/2022] [Indexed: 12/10/2022]
Abstract
Recently, high-entropy alloys (HEAs) and HEA-type compounds have been extensively studied in the fields of material science and engineering. In this article, we report on the synthesis of a layered system MBi2Te4 where the M site possesses low-, middle-, and high-entropy states. The samples with M = Pb, Ag1/3Pb1/3Bi1/3, and Ag1/5In1/5Sn1/5Pb1/5Bi1/5 were newly synthesized and the crystal structure was examined by synchrotron X-ray diffraction and Rietveld refinement. We found that the M-Te2 distance was systematically compressed with decreasing lattice constants, where the configurational entropy of mixing at the M site is also systematically increased. The details of structural refinements and the electrical transport property are presented.
Collapse
|
6
|
Origin of Selective Nitrate Removal by Ni 2+–Al 3+ Layered Double Hydroxides in Aqueous Media and Its Application Potential in Seawater Purification. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2022. [DOI: 10.1246/bcsj.20220032] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
7
|
Specific lift-up behaviour of acetate-intercalated layered yttrium hydroxide interlayer in water: application for heterogeneous Brønsted base catalysts toward Knoevenagel reactions. Catal Sci Technol 2022. [DOI: 10.1039/d1cy02328d] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The basal (00l) plane of acetate-intercalated layered yttrium hydroxide (CH3COO−/Y-LRH), synthesised by an anion exchange using Cl−/Y-LRH as a parent material, increased in water, and the lifted-up layered structure was generated immediately.
Collapse
|
8
|
Important Roles of Water Clusters Confined in a Nanospace as Revealed by a Synchrotron X-ray Diffraction Study. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2021; 37:10469-10480. [PMID: 34427085 DOI: 10.1021/acs.langmuir.1c01322] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/13/2023]
Abstract
States of water molecules confined in a nanospace designed by montmorillonite (negatively charged silicate layer) and charge compensating benzylammonium were investigated. Caffeine was used as a probe because of its compatibility for the fine structure of the interlayer water. Powder synchrotron radiation X-ray diffraction (SXRD) and adsorption isotherms of the water vapor revealed a metastable structure of bimolecular water layers (2WLs) in the interlayer space. Water molecules readily penetrated to expand the interlayer space to 0.56 nm. The interlayer space did not increase further even in the presence of excess water. According to the isosteric heat of water, the expansion was limited because of moderate hydration as forming 2WLs. Caffeine molecules replaced a part of the water molecules in the 2WLs to expand the interlayer space to 0.65 nm. Time-resolved SXRD with an accumulation time of 500 ms revealed that the interlayer expansion reached a steady state within a few minutes. The caffeine intercalation proceeded, involving a change in the molecular orientation that increased the contact area of the caffeine molecules. The interlayer expansion was limited in all the solvents examined (mixtures of water with methanol, ethanol, acetone, and tetrahydrofuran), while the packing density of the incorporated caffeine was maximized in the absence of an organic solvent. The water molecules confined in the interlayer space acted as an actuator to accommodate a large quantity of amphiphilic molecules by adapting the nanostructure, which was achieved by releasing the confined water molecules.
Collapse
|
9
|
Kinetically Stabilized Cation Arrangement in Li 3 YCl 6 Superionic Conductor during Solid-State Reaction. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2021; 8:e2101413. [PMID: 34138514 PMCID: PMC8336504 DOI: 10.1002/advs.202101413] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2021] [Revised: 05/10/2021] [Indexed: 05/06/2023]
Abstract
The main approach for exploring metastable materials is via trial-and-error synthesis, and there is limited understanding of how metastable materials are kinetically stabilized. In this study, a metastable phase superionic conductor, β-Li3 YCl6 , is discovered through in situ X-ray diffraction after heating a mixture of LiCl and YCl3 powders. While Cl- arrangement is represented as a hexagonal close packed structure in both metastable β-Li3 YCl6 synthesized below 600 K and stable α-Li3 YCl6 above 600 K, the arrangement of Li+ and Y3+ in β-Li3 YCl6 determined by neutron diffraction brought about the cell with a 1/√3 a-axis and a similar c-axis of stable α-Li3 YCl6 . Higher Li+ ion conductivity and lower activation energy for Li+ transport are observed in comparison with α-Li3 YCl6 . The computationally calculated low migration barrier of Li+ supports the low activation energy for Li+ conduction, and the calculated high migration barrier of Y3+ kinetically stabilizes this metastable phase by impeding phase transformation to α-Li3 YCl6 . This work shows that the combination of in situ observation of solid-state reactions and computation of the migration energy can facilitate the comprehension of the solid-state reactions allowing kinetic stabilization of metastable materials, and can enable the discovery of new metastable materials in a short time.
Collapse
|
10
|
Observing and Modeling the Sequential Pairwise Reactions that Drive Solid-State Ceramic Synthesis. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2021; 33:e2100312. [PMID: 33949743 DOI: 10.1002/adma.202100312] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Revised: 03/04/2021] [Indexed: 06/12/2023]
Abstract
Solid-state synthesis from powder precursors is the primary processing route to advanced multicomponent ceramic materials. Designing reaction conditions and precursors for ceramic synthesis can be a laborious, trial-and-error process, as heterogeneous mixtures of precursors often evolve through a complicated series of reaction intermediates. Here, ab initio thermodynamics is used to model which pair of precursors has the most reactive interface, enabling the understanding and anticipation of which non-equilibrium intermediates form in the early stages of a solid-state reaction. In situ X-ray diffraction and in situ electron microscopy are then used to observe how these initial intermediates influence phase evolution in the synthesis of the classic high-temperature superconductor YBa2 Cu3 O6+ x (YBCO). The model developed herein rationalizes how the replacement of the traditional BaCO3 precursor with BaO2 redirects phase evolution through a low-temperature eutectic melt, facilitating the formation of YBCO in 30 min instead of 12+ h. Precursor selection plays an important role in tuning the thermodynamics of interfacial reactions and emerges as an important design parameter in planning kinetically favorable synthesis pathways to complex ceramic materials.
Collapse
|
11
|
Abstract
β-Li3PS4 is a solid electrolyte with high Li+ conductivity, applicable to sulfide-based all-solid-state batteries. While a β-Li3PS4-synthesized by solid-state reaction forms only in a narrow 300-450 °C temperature range upon heating, β-Li3PS4 is readily available by liquid-phase synthesis through low-temperature thermal decomposition of complexes composed of PS43- and various organic solvents. However, the conversion mechanism of β-Li3PS4 from these complexes is not yet understood. Herein, we proposed the synthesis mechanism of β-Li3PS4 from Li3PS4·acetonitrile (Li3PS4·ACN) and Li3PS4·1,2-dimethoxyethane (Li3PS4·DME), whose structural similarity with β-Li3PS4 would reduce the nucleation barrier for the formation of β-Li3PS4. Synchrotron X-ray diffraction clarified that both complexes possess similar layered structures consisting of alternating Li2PS4- and Li+-ACN/DME layers. ACN/DME was removed from these complexes upon heating, and rotation of the PS4 tetrahedra induced a uniaxial compression to form the β-Li3PS4 framework.
Collapse
|
12
|
Size effect of the guest cation on the AlO 4 framework in aluminate sodalite-type oxides M 8[Al 12O 24](SO 4) 2 (M = Sr 2+ and Ca 2+) in the I43m phase. ACTA CRYSTALLOGRAPHICA SECTION B, STRUCTURAL SCIENCE, CRYSTAL ENGINEERING AND MATERIALS 2021; 77:186-192. [PMID: 33843725 DOI: 10.1107/s2052520621000238] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Accepted: 01/07/2021] [Indexed: 06/12/2023]
Abstract
Sr8[Al12O24](SO4)2 (SAS) and Ca8[Al12O24](SO4)2 (CAS) are members of the aluminate sodalite-type oxides with the general chemical formula M8[Al12O24](XO4)2 (M2+ is the guest cation and XO42- is the guest anion). To discuss the role of the guest cations (M2+ = Sr2+ and Ca2+) on the rotation of AlO4 in the oxygen tetrahedral framework in the I43m phase, the crystal structure parameters and the probability density function of the guest ions in SAS and CAS have been investigated via synchrotron radiation X-ray powder diffraction by considering Gram-Charlier expansions. The interatomic distances between the M2+ and O2- ions evaluated from the maximum positions in the probability density distribution are almost equal to the sum of the ideal ionic radii of the M2+ and O2- ions. This result suggests that the geometry of the AlO4 tetrahedral framework and the fluctuation of the guest ions are mainly caused by steric effects between the M2+ and O2- ions.
Collapse
|
13
|
Structural Transition with a Sharp Change in the Electrical Resistivity and Spin-Orbit Mott Insulating State in a Rhenium Oxide, Sr 3Re 2O 9. Inorg Chem 2021; 60:507-514. [PMID: 33395280 DOI: 10.1021/acs.inorgchem.0c02750] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We report the successful synthesis, crystal structure, and electrical properties of Sr3Re2O9, which contains Re6+ with the 5d1 configuration. This compound is isostructural with Ba3Re2O9 and shows a first-order structural phase transition at ∼370 K. The low-temperature (LT) phase crystallizes in a hettotype structure of Ba3Re2O9, which is different from that of the LT phase of Sr3W2O9, suggesting that the electronic state of Re6+ plays an important role in determining the crystal structure of the LT phase. The structural transition is accompanied by a sharp change in the electrical resistivity. This is likely a metal-insulator transition, as suggested by the electronic band calculation and magnetic susceptibility. In the LT phase, the ReO6 octahedra are rotated in a pseudo-a0a0a+ manner in Glazer notation, which corresponds to C-type orbital ordering. Paramagnetic dipole moments were confirmed to exist in the LT phase by muon spin rotation and relaxation measurements. However, the dipole moments shrink greatly because of the strong spin-orbit coupling in the Re ions. Thus, the electronic state of the LT phase corresponds to a Mott insulating state with strong spin-orbit interactions at the Re sites.
Collapse
|
14
|
Evolution of two bulk-superconducting phases in Sr 0.5RE 0.5FBiS 2 (RE: La, Ce, Pr, Nd, Sm) by external hydrostatic pressure effect. Sci Rep 2020; 10:12880. [PMID: 32732897 PMCID: PMC7393496 DOI: 10.1038/s41598-020-69889-w] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2020] [Accepted: 07/21/2020] [Indexed: 12/02/2022] Open
Abstract
Polycrystalline samples of Sr0.5RE0.5FBiS2 (RE: La, Ce, Pr, Nd, and Sm) were synthesized via the solid-state reaction and characterized using synchrotron X-ray diffraction. Although all the Sr0.5RE0.5FBiS2 samples exhibited superconductivity at transition temperatures (Tc) within the range of 2.1-2.7 K under ambient pressure, the estimated superconducting volume fraction was small, which indicates non-bulk nature of superconductivity in those samples under ambient pressure. A dramatic increase in shielding fraction, which indicates the emergence of the bulk superconductivity was achieved by applying external hydrostatic pressures. We found that two phases, low-P phases with Tc = 2.5-2.8 K and high-P phases with Tc = 10.0-10.8 K, were induced by the pressure effect for samples with RE = La, Ce, Pr, and Nd. Pressure-Tc phase diagrams indicated that the critical pressure for the emergence of the high-P phase tends to increase with decreasing ionic radius of the doped RE ions, which was explained by the correlation between external and chemical pressure effects. According to the high-pressure X-ray diffraction measurements of Sr0.5La0.5FBiS2, a structural phase transition from tetragonal to monoclinic also occurred at approximately 1.1 GPa. Bulk superconducting phases in Sr0.5RE0.5FBiS2 induced by the external hydrostatic pressure effect are expected to be useful for understanding the effects of both external and chemical pressures to the emergence of bulk superconductivity and pairing mechanisms in BiCh2-based superconductors.
Collapse
|
15
|
Crystal Structure and Thermoelectric Transport Properties of As-Doped Layered Pnictogen Oxyselenides NdO 0.8F 0.2Sb 1-xAs xSe 2. MATERIALS 2020; 13:ma13092164. [PMID: 32392874 PMCID: PMC7254281 DOI: 10.3390/ma13092164] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/10/2020] [Revised: 04/27/2020] [Accepted: 05/04/2020] [Indexed: 11/21/2022]
Abstract
We report the synthesis and thermoelectric transport properties of As-doped layered pnictogen oxyselenides NdO0.8F0.2Sb1−xAsxSe2 (x ≤ 0.6), which are predicted to show high-performance thermoelectric properties based on first-principles calculation. The crystal structure of these compounds belongs to the tetragonal P4/nmm space group (No. 129) at room temperature. The lattice parameter c decreases with increasing x, while a remains almost unchanged among the samples. Despite isovalent substitution of As for Sb, electrical resistivity significantly rises with increasing x. Very low thermal conductivity of less than 0.8 Wm−1K−1 is observed at temperatures between 300 and 673 K for all the examined samples. For As-doped samples, the thermal conductivity further decreases above 600 K. Temperature-dependent synchrotron X-ray diffraction indicates that an anomaly also occurs in the c-axis length at around 600 K, which may relate to the thermal transport properties.
Collapse
|
16
|
Antithermal Quenching of Luminescence in Zero-Dimensional Hybrid Metal Halide Solids. J Phys Chem Lett 2020; 11:2902-2909. [PMID: 32212731 DOI: 10.1021/acs.jpclett.0c00293] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/10/2023]
Abstract
Zero-dimensional (0D) hybrid metal halides have emerged as a new generation of luminescent phosphors owing to their high radiative recombination rates, which, akin to their three-dimensional cousins, commonly demonstrate thermal quenching of luminescence. Here, we report on the finding of antithermal quenching of luminescence in 0D hybrid metal halides. Using (C9NH20)2SnBr4 single crystals as an example system, we show that 0D metal halides can demonstrate antithermal quenching of luminescence. A combination of experimental characterizations and first-principles calculations suggests that antithermal quenching of luminescence is associated with trap states introduced by structural defects in (C9NH20)2SnBr4. Importantly, we find that antithermal quenching of luminescence is not only limited to (C9NH20)2SnBr4 but also exists in other 0D metal halides. Our work highlights the important role of defects in impacting photophysical properties of hybrid metal halides and may stimulate new efforts to explore metal halides exhibiting antithermal quenching of luminescence at higher temperatures.
Collapse
|
17
|
Flux Growth and Superconducting Properties of (Ce,Pr)OBiS 2 Single Crystals. Front Chem 2020; 8:44. [PMID: 32117872 PMCID: PMC7010857 DOI: 10.3389/fchem.2020.00044] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Accepted: 01/14/2020] [Indexed: 11/13/2022] Open
Abstract
Ce1−xPrxOBiS2 (0. 1 ≤ x ≤ 0.9) single crystals were grown using a CsCl flux method. Their structural and physical properties were examined by X-ray diffraction, X-ray absorption, transmission electron microscopy, and electrical resistivity. All of the Ce1−xPrxOBiS2 single crystals with 0.1 ≤ x ≤ 0.9 exhibited tetragonal phase. With increasing Pr content, the a-axis and c-axis lattice parameters decreased and increased, respectively. Transmission electron microscope analysis of Ce0.1Pr0.9OBiS2 (x = 0.9) single crystal showed no stacking faults. Atomic-resolution energy dispersive X-ray spectrometry mapping revealed that Bi, Ce/Pr, O, and S occupied different crystallographic sites, while Ce and Pr randomly occupied the same sites. X-ray absorption spectra showed that an increase of the Pr ratio increased the ratio of Ce4+/Ce3+. All of the Ce1−xPrxOBiS2 crystals showed superconducting transition, with a maximum transition temperature of ~4 K at x = 0.9.
Collapse
|
18
|
Charge ordering and successive phase transitions of mixed-valence iron oxide GdBaFe2O5. J SOLID STATE CHEM 2020. [DOI: 10.1016/j.jssc.2019.121069] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
19
|
Development of a Novel Time-Resolved Synchrotron-Radiation X-ray Diffraction Measurement System for In Situ Observation of Crystal Structure in Aqueous Solution during Chemical Reaction: Application to the Anion-Exchange Reaction of a Layered Double Hydroxide from Chloride to Nitrate. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 2019. [DOI: 10.1246/bcsj.20190244] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
|
20
|
Defective [Bi 2 O 2 ] 2+ Layers Exhibiting Ultrabroad Near-Infrared Luminescence. Chemistry 2019; 25:12842-12848. [PMID: 31376189 DOI: 10.1002/chem.201903403] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2019] [Indexed: 02/04/2023]
Abstract
Aurivillius phases have been routinely known as excellent ferroelectrics and have rarely been deemed as materials that luminesce in the near-infrared (NIR) region. Herein, it is shown that the Aurivillius phases can demonstrate broadband NIR luminescence that covers telecommunication and biological optical windows. Experimental characterization of the model system Bi2.14 Sr0.75 Ta2 O9-x , combined with theoretical calculations, help to establish that the NIR luminescence originates from defective [Bi2 O2 ]2+ layers. Importantly, the generality of this finding is validated based on observations of a rich bank of NIR luminescence characteristics in other Aurivillius phases. This work highlights that incorporating defects into infinitely repeating [Bi2 O2 ]2+ layers can be used as a powerful tool to space-selectively impart unusual luminescence emitters to Aurivillius-phase ferroelectrics, which not only offers an optical probe for the examination of defect states in ferroelectrics, but also provides possibilities for coupling of the ferroelectric property with NIR luminescence.
Collapse
|
21
|
Hydrothermal Synthesis and Crystal Structure of a (Ba 0.54K 0.46) 4Bi 4O 12 Double-Perovskite Superconductor with Onset of the Transition Tc ∼ 30 K. Inorg Chem 2019; 58:11997-12001. [PMID: 31469548 DOI: 10.1021/acs.inorgchem.9b01768] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
A new superconducting double perovskite was successfully synthesized by a low-temperature hydrothermal reaction at 240 °C. The crystal structure refinement of this double perovskite was done by single-crystal X-ray diffraction, and it had a cubic unit cell of a = 8.5207(2) Å with space group Im3̅m (No. 229). This superconducting double-perovskite chemical composition was estimated by electron probe microanalysis and was similar to the refined data. The superconducting transition temperature of the double perovskite was ∼30 K; the electrical resistivity began to fall at ∼25 K, and zero resistivity occurred below 7 K. Moreover, temperature-dependent resistivity under various magnetic fields and isothermal magnetization measurements ensured the nature of a type II superconductor for the sample. Finally, the metallic nature of the material was investigated by a first-principles study.
Collapse
|
22
|
An electronic structure governed by the displacement of the indium site in In-S 6 octahedra: LnOInS 2 (Ln = La, Ce, and Pr). Dalton Trans 2019; 48:12272-12278. [PMID: 31339138 DOI: 10.1039/c9dt01562k] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
An extremely large displacement of the indium site in In-S6 octahedra in LnOInS2 (Ln = La, Ce, and Pr) was found in synchrotron X-ray diffraction. LaOInS2 with off-center indium in In-S6 octahedra exhibited a wider optical band gap than CeOInS2 and PrOInS2 with on-center indium. Therefore, the electronic structure of LnOInS2 is governed by the indium site with an extremely large displacement. All LnOInS2 produced H2 gas under visible light irradiation in the presence of sacrificial electron donors.
Collapse
|
23
|
Time-resolved structure analysis of piezoelectric crystals resonantly vibrating under alternating electric field. Acta Crystallogr A Found Adv 2019. [DOI: 10.1107/s2053273319089253] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/03/2023] Open
|
24
|
Why Do Carbonate Anions Have Extremely High Stability in the Interlayer Space of Layered Double Hydroxides? Case Study of Layered Double Hydroxide Consisting of Mg and Al (Mg/Al = 2). Inorg Chem 2019; 58:10928-10935. [DOI: 10.1021/acs.inorgchem.9b01365] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
|
25
|
Doping-Induced Polymorph and Carrier Polarity Changes in Thermoelectric Ag(Bi,Sb)Se 2 Solid Solution. Inorg Chem 2019; 58:7628-7633. [PMID: 31074617 DOI: 10.1021/acs.inorgchem.9b01038] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Silver bismuth diselenide (AgBiSe2) is an n-type thermoelectric material that exhibits a complex structural phase transition from the hexagonal to cubic phase, while silver antimony diselenide (AgSbSe2) is a p-type thermoelectric material that crystallizes in the cubic phase at all temperatures. Here, we investigate the crystal structure and thermoelectric properties of Ag(Bi,Sb)Se2 solid solution, employing AgBi0.9Sb0.1Se2 and AgBi0.7Sb0.3Se2 as representative samples. The carrier polarity of AgBi0.9Sb0.1Se2 is converted from the n-type to p-type by Pb doping, accompanied by a polymorphic change to the cubic phase. It is difficult to obtain highly conductive p-type hexagonal AgBiSe2-based materials, although first-principles calculations predict high-performance thermoelectric properties for these systems. We also demonstrate that cubic AgBi0.7Sb0.3Se2 undergoes a polymorphic change to the hexagonal phase upon Nb doping. The present study show that polymorphic changes inevitably occurred upon Pb/Nb doping to optimize thermoelectric properties of Ag(Bi,Sb)Se2 solid solution.
Collapse
|
26
|
Abstract
The pyrochlore-type Ca2Bi2O7 and Sr2Bi2O7 have been synthesized from a low-temperature hydrothermal route using NaBiO3·nH2O as a starting material. The crystal structures of these compounds were refined using synchrotron powder X-ray diffraction data. The cell parameters were found to be a = 10.75021 (5) Å and 10.94132 (6) Å for Ca2Bi2O7 and Sr2Bi2O7, respectively. Density functional theory calculations showed the metallic band structure, but the negligible mixing of O2 2p bands with the A-site alkaline-earth-metal states and weak overlap with the conduction bands result in the semiconducting behavior.
Collapse
|
27
|
X-ray-activated long persistent phosphors featuring strong UVC afterglow emissions. LIGHT, SCIENCE & APPLICATIONS 2018; 7:88. [PMID: 30455871 PMCID: PMC6234205 DOI: 10.1038/s41377-018-0089-7] [Citation(s) in RCA: 62] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2018] [Revised: 10/26/2018] [Accepted: 10/26/2018] [Indexed: 05/12/2023]
Abstract
Phosphors emitting visible and near-infrared persistent luminescence have been explored extensively owing to their unusual properties and commercial interest in their applications such as glow-in-the-dark paints, optical information storage, and in vivo bioimaging. However, no persistent phosphor that features emissions in the ultraviolet C range (200-280 nm) has been known to exist so far. Here, we demonstrate a strategy for creating a new generation of persistent phosphor that exhibits strong ultraviolet C emission with an initial power density over 10 milliwatts per square meter and an afterglow of more than 2 h. Experimental characterizations coupled with first-principles calculations have revealed that structural defects associated with oxygen introduction-induced anion vacancies in fluoride elpasolite can function as electron traps, which capture and store a large number of electrons triggered by X-ray irradiation. Notably, we show that the ultraviolet C afterglow intensity of the yielded phosphor is sufficiently strong for sterilization. Our discovery of this ultraviolet C afterglow opens up new avenues for research on persistent phosphors, and it offers new perspectives on their applications in terms of sterilization, disinfection, drug release, cancer treatment, anti-counterfeiting, and beyond.
Collapse
|
28
|
Na 1-xSn 2P 2 as a new member of van der Waals-type layered tin pnictide superconductors. Sci Rep 2018; 8:12852. [PMID: 30150765 PMCID: PMC6110830 DOI: 10.1038/s41598-018-31295-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 07/25/2018] [Indexed: 11/30/2022] Open
Abstract
Superconductors with a van der Waals (vdW) structure have attracted a considerable interest because of the possibility for truly two-dimensional (2D) superconducting systems. We recently reported NaSn2As2 as a novel vdW-type superconductor with transition temperature (Tc) of 1.3 K. Herein, we present the crystal structure and superconductivity of new material Na1−xSn2P2 with Tc = 2.0 K. Its crystal structure consists of two layers of a buckled honeycomb network of SnP, bound by the vdW forces and separated by Na ions, as similar to that of NaSn2As2. Amount of Na deficiency (x) was estimated to be 0.074(18) using synchrotron X-ray diffraction. Bulk nature of superconductivity was confirmed by the measurements of electrical resistivity, magnetic susceptibility, and specific heat. First-principles calculation using density functional theory shows that Na1−xSn2P2 and NaSn2As2 have comparable electronic structure, suggesting higher Tc of Na1−xSn2P2 resulted from increased density of states at the Fermi level due to Na deficiency. Because there are various structural analogues with tin-pnictide (SnPn) conducting layers, our results indicate that SnPn-based layered compounds can be categorized into a novel family of vdW-type superconductors, providing a new platform for studies on physics and chemistry of low-dimensional superconductors.
Collapse
|
29
|
Abstract
The crystal structure of NaBiO3· nH2O was refined using synchrotron powder X-ray diffraction and was assigned to a trigonal unit cell (space group P3̅) consisting of layered structures formed by edge-sharing BiO6 octahedra and consisting of an interlayer composed of water molecules sandwiched between two layers of sodium atoms, perpendicular to the c axis. An intermediate phase was observed during the dehydration of the hydrated compound. Density of state calculations showed hybridization of the Bi 6s and O 2p orbitals at the bottom of the conduction bands for both the hydrated and the dehydrated phases, which narrows the band gap and promotes their photocatalytic activity in the visible region.
Collapse
|
30
|
Ion-Exchangeable Microporous Polyoxometalate Compounds with Off-Center Dopants Exhibiting Unconventional Luminescence. Chemistry 2018; 24:9976-9982. [PMID: 29683534 DOI: 10.1002/chem.201801829] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Indexed: 11/05/2022]
Abstract
The synthesis of luminescent polyoxometalates (POMs) typically relies on the assembly of POM ligands with rare earth or transition metals, placing significant constraints on the composition, structure, and hence the luminescence properties of the resultant systems. Herein, we show that the ion-exchange strategy can be used for the synthesis of novel POM-based luminescent materials. We demonstrate that introducing bismuth ions into an ion-exchangeable, microporous POM compound yields an unconventional system luminescing in the near-infrared region. Experimental characterization, coupled with quantum chemical calculations, confirms that bismuth ions site-specifically occupy an off-center site in the lattice, and have an asymmetric coordination geometry unattainable by other means, thus giving rise to peculiar emission. Our findings offer an effective strategy for the synthesis of POM-based luminescent materials, and the design concept may potentially be adapted to the creation of POM-based systems with other functionalities.
Collapse
|
31
|
Transformation of Perovskite BaBiO 3 into Layered BaBiO 2.5 Crystals Featuring Unusual Chemical Bonding and Luminescence. Chemistry 2018; 24:8875-8882. [PMID: 29655241 DOI: 10.1002/chem.201801257] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2018] [Revised: 04/09/2018] [Indexed: 11/09/2022]
Abstract
Engineering oxygen coordination environments of cations in oxides has received intense interest thanks to the opportunities for the discovery of novel oxides with unusual properties. Herein, the synthesis of stoichiometric layered BaBiO2.5 by a nontopotactic phase transformation of perovskite BaBiO3 is presented. By analyzing the synchrotron X-ray diffraction data by the maximum-entropy method/Rietveld technique, it was found that Bi is involved in an unusual chemical bonding situation with four oxygen atoms featuring one ionic bond and three covalent bonds, which results in an asymmetric coordination geometry. Photophysical characterization revealed that this peculiar structure shows near-infrared luminescence differing from that of conventional Bi-containing compounds. Experimental and theoretical results led to the proposal of an excitonic nature of the luminescence. This work highlights that synthesizing materials with uncommon Bi-O bonding and Bi coordination geometry provides a pathway to the discovery of systems with new functionalities. This could inspire interest in the exploration of a range of materials containing heavier p-block elements with prospects for finding systems with unusual properties.
Collapse
|
32
|
Cs 4PbBr 6/CsPbBr 3 Perovskite Composites with Near-Unity Luminescence Quantum Yield: Large-Scale Synthesis, Luminescence and Formation Mechanism, and White Light-Emitting Diode Application. ACS APPLIED MATERIALS & INTERFACES 2018; 10:15905-15912. [PMID: 29668249 DOI: 10.1021/acsami.8b04556] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
All-inorganic perovskites have emerged as a new class of phosphor materials owing to their outstanding optical properties. Zero-dimensional inorganic perovskites, in particular the Cs4PbBr6-related systems, are inspiring intensive research owing to the high photoluminescence quantum yield (PLQY) and good stability. However, synthesizing such perovskites with high PLQYs through an environment-friendly, cost-effective, scalable, and high-yield approach remains challenging, and their luminescence mechanisms has been elusive. Here, we report a simple, scalable, room-temperature self-assembly strategy for the synthesis of Cs4PbBr6/CsPbBr3 perovskite composites with near-unity PLQY (95%), high product yield (71%), and good stability using low-cost, low-toxicity chemicals as precursors. A broad range of experimental and theoretical characterizations suggest that the high-efficiency PL originates from CsPbBr3 nanocrystals well passivated by the zero-dimensional Cs4PbBr6 matrix that forms based on a dissolution-crystallization process. These findings underscore the importance in accurately identifying the phase purity of zero-dimensional perovskites by synchrotron X-ray technique to gain deep insights into the structure-property relationship. Additionally, we demonstrate that green-emitting Cs4PbBr6/CsPbBr3, combined with red-emitting K2SiF6:Mn4+, can be used for the construction of WLEDs. Our work may pave the way for the use of such composite perovskites as highly luminescent emitters in various applications such as lighting, displays, and other optoelectronic and photonic devices.
Collapse
|
33
|
Abstract
Ce1- xPr xOBiS2 powders and Ce0.5Pr0.5OBiS2 single crystals were synthesized and their structure and superconductive properties were examined by X-ray diffraction, X-ray absorption, electronic resistivity, and magnetization. While PrOBiS2 was found to be in a monoclinic phase with one-dimensional Bi-S zigzag chains showing no superconductive transition above 0.1 K, CeOBiS2 was in a tetragonal phase with two-dimensional Bi-S planes showing zero resistivity below 1.3 K. In the range x = 0.3-0.9 in Ce1- xPr xOBiS2, both monoclinic and tetragonal phases were formed together with zero resistivity up to a maximum temperature of 2.2 K. A Ce0.5Pr0.5OBiS2 single crystal, which showed both zero resistivity and a decrease in magnetization at ∼2.4 K, presented a tetragonal structure. Short Bi-S bonding in flat two-dimensional Bi-S planes and mixed Ce3+/Ce4+ were characteristic features of the Ce0.5Pr0.5OBiS2 single crystal, which presumably triggered its superconductivity.
Collapse
|
34
|
Effect of Te substitution on crystal structure and transport properties of AgBiSe2thermoelectric material. Dalton Trans 2018; 47:2575-2580. [DOI: 10.1039/c7dt04821a] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Reduced lattice thermal conductivity of Te-substituted AgBiSe2was qualitatively described using the point defect scattering model.
Collapse
|
35
|
High-throughput powder diffraction measurement system consisting of multiple MYTHEN detectors at beamline BL02B2 of SPring-8. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2017; 88:085111. [PMID: 28863664 DOI: 10.1063/1.4999454] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/10/2023]
Abstract
In this study, we developed a user-friendly automatic powder diffraction measurement system for Debye-Scherrer geometry using a capillary sample at beamline BL02B2 of SPring-8. The measurement system consists of six one-dimensional solid-state (MYTHEN) detectors, a compact auto-sampler, wide-range temperature control systems, and a gas handling system. This system enables to do the automatic measurement of temperature dependence of the diffraction patterns for multiple samples. We introduced two measurement modes in the MYTHEN system and developed new attachments for the sample environment such as a gas handling system. The measurement modes and the attachments can offer in situ and/or time-resolved measurements in an extended temperature range between 25 K and 1473 K and various gas atmospheres and pressures. The results of the commissioning and performance measurements using reference materials (NIST CeO2 674b and Si 640c), V2O3 and Ti2O3, and a nanoporous coordination polymer are presented.
Collapse
|
36
|
Hydrothermal Synthesis, Crystal Structure, and Visible-Region Photocatalytic Activity of BaBi2
O6. ChemistrySelect 2017. [DOI: 10.1002/slct.201700973] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
|
37
|
Hydrothermal Synthesis, Structure, and Superconductivity of Simple Cubic Perovskite (Ba 0.62K 0.38)(Bi 0.92Mg 0.08)O 3 with T c ∼ 30 K. Inorg Chem 2017; 56:3174-3181. [PMID: 28233995 DOI: 10.1021/acs.inorgchem.6b01853] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
We have synthesized a new superconducting perovskite bismuth oxide by a facile hydrothermal route at 220 °C. The choice of starting materials, their mixing ratios, and the hydrothermal reaction temperature was crucial for obtaining products with superior superconducting properties. The structure of the powder sample was investigated using laboratory X-ray diffraction, high-resolution synchrotron X-ray diffraction (SXRD) data, and electron diffraction (ED) patterns [transmission electron microscopy (TEM) analysis]. The refinement of SXRD data confirmed a simple perovskite-type structure with a cubic cell of a = 4.27864(2) Å [space group Pm3̅m (No. 221)]. Elemental analysis detected magnesium in the final products, and a refinement based on SXRD and inductively coupled plasma data yielded an ideal undistorted simple cubic perovskite-type structure, with the chemical composition (Ba0.62K0.38)(Bi0.92Mg0.08)O3. ED patterns also confirmed the simple cubic perovskite structure; the cube-shaped microstructures and compositional homogeneity on the nanoscale were verified by scanning electron microscopy and TEM analyses, respectively. The fabricated compound exhibited a large shielding volume fraction of about 98% with a maximum Tcmag of ∼30 K, which was supported by the measured bismuth valence as well. Its electrical resistivity dropped at ∼21 K, and zero resistivity was observed below 7 K. The compound underwent thermal decomposition above 400 °C. Finally, the calculated band structure showed a metallic behavior for this hydrothermally synthesized bismuth oxide.
Collapse
|
38
|
Hydrothermal synthesis and crystal structure of a new lithium copper bismuth oxide, LiCuBiO 4. J SOLID STATE CHEM 2017. [DOI: 10.1016/j.jssc.2016.10.003] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
|
39
|
Adsorption Behavior of Rare Earth Metal Cations in the Interlayer Space of γ-ZrP. LANGMUIR : THE ACS JOURNAL OF SURFACES AND COLLOIDS 2016; 32:9993-9999. [PMID: 27652606 DOI: 10.1021/acs.langmuir.6b02747] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Adsorption competencies of rare earth metal cations in γ-zirconium phosphate were examined by ICP, synchrotron X-ray diffraction (SXRD), and ab initio simulation. The adsorption amounts are around 0.06-0.10 per zirconium phosphate. From the SXRD patterns of the adsorbed samples, the basal spacing estimated by c sin β increased linearly with an increasing ionic radius of rare earth metal cation, though a and b lattice constants show no change. These SXRD patterns can be classified into four groups that have different super lattices. The four superlattices have multiplicities of x131, x241, and x221 for the xabc axis, and the location of the rare earth metal cation in the original unit cell changes depending on the superlattice cell. In the x131 superlattice, Yb and Er occupied the site near the zirconium phosphate layer, though La and Ce in the x221 superlattice remained in the center position between the phosphate sheet. For the ab initio simulation of γ-ZrP with the typical rare earth metal cations (Tb, Eu, Dy, and La), the results of simulation show a similar tendency of the position estimated by SXRD refinements.
Collapse
|
40
|
Abstract
Because the functions of polar materials are governed primarily by their polarization response to external stimuli, the majority of studies have focused on controlling polar lattice distortions. In some perovskite oxides, polar distortions coexist with nonpolar tilts and rotations of oxygen octahedra. The interplay between nonpolar and polar instabilities appears to play a crucial role, raising the question of how to design materials by exploiting their coupling. Here, we introduce the concept of ‘polarization twist’, which offers enhanced control over piezoelectric responses in polar materials. Our experimental and theoretical studies provide direct evidence that a ferrielectric perovskite exhibits a large piezoelectric response because of extended polar distortion, accompanied by nonpolar octahedral rotations, as if twisted polarization relaxes under electric fields. The concept underlying the polarization twist opens new possibilities for developing alternative materials in bulk and thin-film forms.
Collapse
|
41
|
Unconventional Luminescent Centers in Metastable Phases Created by Topochemical Reduction Reactions. Angew Chem Int Ed Engl 2016; 55:4967-71. [DOI: 10.1002/anie.201601191] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Indexed: 11/09/2022]
|
42
|
Control of magneto-transport characteristics of Co-doped ZnO by electron beam irradiation. RSC Adv 2016. [DOI: 10.1039/c6ra02641a] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Electron beam irradiation can be used to remove shallow donor type hydrogen located in Zn(Co)–O bonding centers in Co-doped ZnO, which enables to modify the conduction band and the magneto-transport characteristics of Co-doped ZnO.
Collapse
|
43
|
Structural Difference in Superconductive and Nonsuperconductive Bi-S Planes within Bi4O4Bi2S4 Blocks. Inorg Chem 2015; 54:10462-7. [PMID: 26479778 DOI: 10.1021/acs.inorgchem.5b01919] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The relationship between the structure and superconductivity of Bi4O4S3 powders synthesized by heating under ambient and high pressures was investigated using synchrotron X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) observation. The Bi4O4S3 powders synthesized under ambient pressure exhibited a strong superconductivity (diamagnetic) signal and zero resistivity below ∼4.5 K, while the Bi4O4S3 powder synthesized by the high-pressure method exhibited a low-intensity signal down to 2 K. Further annealing of the latter Bi4O4S3 powder under ambient pressure led to the development of a strong signal and zero resistivity. The crystal structures of all Bi4O4S3 phases consisted of Bi4O4Bi2S4 blocks including a Bi-S layer and anion(s) sandwiched between Bi4O4Bi2S4 blocks, but minor structural differences were detected. A comparison of the structures of the superconductive and nonsuperconductive Bi4O4S3 samples suggested that the superconductive Bi4O4S3 phases had slightly smaller lattice parameters. The average structures of the superconductive Bi4O4S3 phases were characterized by a slightly shorter and less bent Bi-S plane. Raman spectroscopy detected vibration of the S-O bonds, which can be attributed to sandwiched anion(s) such as SO4(2-). TEM observation showed stacking faults in the superconductive Bi4O4S3 phases, which indicated local fluctuation of the average structures. The observed superconductivity of Bi4O4S3 was discussed based on impurity phases, enhanced hybridization of the px and py orbitals of the Bi-S plane within Bi4O4Bi2S4 blocks, local fluctuation of the average structures, compositional deviation related to suspicious anion(s) sandwiched between Bi4O4Bi2S4 blocks, and the possibility of suppression of the charge-density-wave state by enriched carrier concentrations.
Collapse
|
44
|
In-plane chemical pressure essential for superconductivity in BiCh2-based (Ch: S, Se) layered structure. Sci Rep 2015; 5:14968. [PMID: 26447333 PMCID: PMC4597362 DOI: 10.1038/srep14968] [Citation(s) in RCA: 91] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2015] [Accepted: 09/14/2015] [Indexed: 11/08/2022] Open
Abstract
BiCh2-based compounds (Ch: S, Se) are a new series of layered superconductors, and the mechanisms for the emergence of superconductivity in these materials have not yet been elucidated. In this study, we investigate the relationship between crystal structure and superconducting properties of the BiCh2-based superconductor family, specifically, optimally doped Ce1-xNdxO0.5F0.5BiS2 and LaO0.5F0.5Bi(S1-ySey)2. We use powder synchrotron X-ray diffraction to determine the crystal structures. We show that the structure parameter essential for the emergence of bulk superconductivity in both systems is the in-plane chemical pressure, rather than Bi-Ch bond lengths or in-plane Ch-Bi-Ch bond angle. Furthermore, we show that the superconducting transition temperature for all REO0.5F0.5BiCh2 superconductors can be determined from the in-plane chemical pressure.
Collapse
|
45
|
Abstract
Hexagonal Lu1-xScxFeO3 (0 ≤ x ≤ 0.8) was directly solidified from an undercooled melt by containerless processing with an aerodynamic levitation furnace. The hexagonal phase-forming region was considerably extended compared to that of the conventional solid-state reaction (x ∼ 0.5). Synchrotron X-ray diffraction measurements revealed that the crystal structure of the hexagonal phase was isomorphous to hexagonal ferroelectric RMnO3 (R = a rare earth ion) with a polar space group of P63cm. As x increased, the a-axis lattice constant decreased linearly, strengthening the antiferromagnetic interaction between the Fe(3+) ions on the a-b plane. Accordingly, the weak ferromagnetic transition temperature increased from 150 K for x = 0 to 175 K for x = 0.7. These transition temperatures were much higher than those of hexagonal Lu1-xScxMnO3. The results indicate that hexagonal Lu1-xScxFeO3 is a suitable alternative magnetic dielectric for use at higher temperatures.
Collapse
|
46
|
Analysis of oxygen vacancy in Co-doped ZnO using the electron density distribution obtained using MEM. NANOSCALE RESEARCH LETTERS 2015; 10:186. [PMID: 25977658 PMCID: PMC4414861 DOI: 10.1186/s11671-015-0887-2] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/16/2014] [Accepted: 03/31/2015] [Indexed: 05/22/2023]
Abstract
Oxygen vacancy (VO) strongly affects the properties of oxides. In this study, we used X-ray diffraction (XRD) to study changes in the VO concentration as a function of the Co-doping level of ZnO. Rietveld refinement yielded a different result from that determined via X-ray photoelectron spectroscopy (XPS), but additional maximum entropy method (MEM) analysis led it to compensate for the difference. VO tended to gradually decrease with increased Co doping, and ferromagnetic behavior was not observed regardless of the Co-doping concentration. MEM analysis demonstrated that reliable information related to the defects in the ZnO-based system can be obtained using X-ray diffraction alone.
Collapse
|
47
|
Fabrication of Barium Titanate Based Ferroelectrics by Containerless Processing. Acta Crystallogr A Found Adv 2014. [DOI: 10.1107/s2053273314099355] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Lead-free ferroelectric materials are desired in our lives owing to the environmental problem, and are anticipated to replace conventional ferroelectrics such as Pb(Zr,Ti)O3(PZT) ceramics. Many researchers have attempted to develop lead-free ceramics whose ferroelectric properties would surpass those of PZT ceramics. Recently, it has been reported that oxygen-deficient hexagonal-BaTiO3which is metastable state of perovskite-BaTiO3exhibits giant dielectric constants over the wide temperature range. Such a metastable material has capability as a lead-free dielectric material with high performance. The containerless processing has an advantage over the other conventional methods in synthesizing metastable materials. It can suppress heterogeneous nucleation from the container wall, and produce the undercooled state below the solidification point of the metastable phase, which is lower than that of the stable phase. The purpose of this study is to synthesize barium titanate based ferroelectrics by the containerless processing as lead-free metastable materials. We developed the aerodynamic levitation furnace which enables us to levitate and melt a sample about 1-3 mm in diameter in containerless condition. Figure 1 shows a schematic view of the aerodynamic levitation furnace. The samples are levitated by the gas jet nozzle, and are melted using the CO2laser radiation. The metastable crystals of the barium titanate based ferroelectrics were fabricated by the aerodynamic levitation furnace. The crystal structure is demonstrated by analyzing high energy synchrotron radiation powder diffraction data. We discuss the prospects of the ferroelectricity on the basis of the determined crystal structure.
Collapse
|
48
|
Valence Electron Distributions in Ferroelectric Barium Titanate Nanopowders. Acta Crystallogr A Found Adv 2014. [DOI: 10.1107/s2053273314092535] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Barium titanate BaTiO3 is one of the most important perovskite-type electroceramics, which undergoes the phase transition at 1300C from cubic to tetragonal, and exhibits ferroelectricity at room temperature. The phase transition depends on the particle size. BaTiO3 powders with the particle sizes less than several tens of nanometers are known to show no phase transition and hence no ferroelectricity at room temperature. The size effect of BaTiO3 is the most important issue in designing small ceramic capacitors with high capacitance. Our group has been devoted to visualizing the electron density distributions of perovskite-type oxides by analyzing the synchrotron-radiation x-ray powder diffraction (SXRD) data measured at SPring-8 using the maximum entropy method (MEM)/Rietveld method [1, 2]. In this study, the distributions of valence electrons in the outer shells of atoms are derived accurately from the SXRD data of BaTiO3 nanopowders to prove the characteristic chemical bondings which govern the ferroelectric phase transition. The powder samples used were 500 and 35 nm in particle sizes. The former showed the phase transition whereas the latter showed no phase transition. The MEM valence electron density studies at 2000C in the cubic structure revealed the clear structural variations that the Ti-O covalent bonding is found in the 500 nm sample, while all the valence electrons are localized at the O sites in the 35 nm sample exactly like an ionic crystal. Ferroelectricity originates from the balance between the long-rage Coulomb force and the short-range repulsion force. The obtained results provide direct experimental evidence that the electron orbitals hybridization on the Ti-O bonds weakens the short-range repulsion force, and causes the second-order Jahn-Teller distortion on the TiO6 octahedron in the 500 nm sample. We consider that the Ti-O bonding in the prototype structure governs the ferroelectric phase transition temperature in BaTiO3.
Collapse
|
49
|
Abstract
Recently, ferroelectricity was discovered in Sn-doped SrTiO3 (abbreviated by SSTO), in which Sr-atom was substituted by a few percent Sn-atom[1]. The ferroelctricity of SSTO was confirmed by means of the appearance of the dielectric anomaly, that reached several thousands and the clear D-E hysteresis loop in low temperature phase. In order to clarify the mechanism of ferroelectric phase transition of SSTO from the viewpoint of the crystal structure, we investigated the average crystal structure and the local structure around the substitutional Sn-atom of SSTO10 (10% Sn concentration, ferroelectric phase transition temperature 180K) by means of synchrotron-radiation powder X-ray diffraction and transmission XAFS spectrum of Sn:K-edge, respectively. From the results of MEM/Rietveld analysis of powder X-ray diffraction data, it was obtained that crystal structure of paraelectric phase of SSTO10 was cubic perovskite structure with the disorder state of Sn-atom. In ferroelectric phase, the crystal system was tetragonal, which was similar in structure to tetragonal ferroelectric structure of BaTiO3, and Sn-atom was order state. XAFS study revealed that the valence of Sn-ion was +2 charge and the local structure of Sn-atom was seemed as being the self-insistent state of SnO crystal structure. However, strangely, the coordination number of the nearest neighbor atom, that is O-atom, was 2 instead of 4. This is a mystery result and we have been analyzing. We have considered that the ferroelectricity of SSTO is induced by the distortion around the subsitituional Sn-atom. At the meeting, we are planning to discuss the precise crystal structure and the mechanism of the ferroelectric phase transition of SSTO.
Collapse
|
50
|
Structure and Anion Exchangeability of Ni-Al-Type Layered Double Hydroxides. Acta Crystallogr A Found Adv 2014. [DOI: 10.1107/s2053273314090846] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
Layered double hydroxide (LDH) is one of promising inorganic materials for cleaning the environmental water polluted by toxic anions. The crystal structure of LDH is composed of the positively-charged metal hydroxide nanosheets and the anions with water molecules intercalated between the nanosheet layers. To put LDHs for practical use, it is necessary to understand why only special anions can be intercalated into the crystal structure from the aqueous solution. In this study, the anion exchange experiments and the synchrotron radiation x-ray powder diffraction measurements of Ni-Al-type LDHs of several kinds of Ni/Al ratios with chlorine and nitrate anions were performed to investigate the relationship between the anion exchange selectivity and crystal structures. The nitrate ion selectivity is normally poor in most of LDHs with different metal ions in the hydroxide nanosheet [1]. However, the nitrate ions were preferred to the chlorine ions in Ni-Al-type LDH when Ni/Al = 4, whereas the chlorine ions were selected when Ni/Al = 2. The crystal structure analysis revealed that the interlayer distance decreased and the thermal motion of the nitrate ions suppressed in Ni-Al-nitrate-type LDH with increasing the Ni/Al ratio, whereas those of the chlorine ions in Ni-Al-chlorine-type LDH increased and enhanced with increasing the Ni/Al ratio. These results indicate that the nitrate ions are more stable than the chlorine ions in the crystal structure of the Ni-Al-type LDH when the positive charge of the nanosheet is small, i.e. the number of anions is small. The short interlayer distance and the small thermal vibration of anions in the crystal structure are the key to understand the anion selectivity of LDH.
Collapse
|