Perovskite-related structures of Ba2YAlO5 and the β and α phases of Ba6Y2Al4O15 containing AlO4 tetrahedra

Single crystals of Ba2YAlO5 and of the α and β phases of Ba6Y2Al4O15 suitable for X-ray structure analysis were obtained via grain growth of polycrystalline samples prepared by solid-state reactions. Ba2YAlO5 was found to have a monoclinic crystal structure, with lattice parameters a = 7.2333 (7), b = 6.0254 (5), c = 7.4294 (7) Å and β = 117.249 (3)°, and to belong to the space group P21/m, while α-Ba6Y2Al4O15 was determined to be monoclinic, with a = 5.9019 (2), b = 7.8744 (3), c = 9.6538 (3) Å and β = 107.7940 (10)°, and the space group Pm, and β-Ba6Y2Al4O15 was found to be monoclinic, with a = 7.8310 (2), b = 5.8990 (2), c = 18.3344 (6) Å and β = 91.6065 (11)°, and the space group P2/c. In each of these compounds, BO6 octahedra in ABO3 perovskite-type structures were replaced by AlO4 tetrahedra and YO6 octahedra. Polycrystalline samples in which some Y atoms were replaced with Eu exhibited orange-red luminescence in the range 580-730 nm in response to exposure to radiation having a wavelength of approximately 250 nm.

New Triclinic Perovskite-Type Oxide Ba5CaFe4O12 for Low-Temperature Operated Chemical Looping Air Separation

We present the discovery of Ba5CaFe4O12, a new iron-based oxide with remarkable properties as a low-temperature driven oxygen storage material (OSM). OSMs, which exhibit selective and rapid oxygen intake and release capabilities, have attracted considerable attention in chemical looping technologies. Specifically, chemical looping air separation (CLAS) has the potential to revolutionize oxygen production as it is one of the most crucial industrial gases. However, the challenge lies in utilizing OSMs for energy-efficient CLAS at lower temperatures. Ba5CaFe4O12, a cost-competitive material, possesses an unprecedented 5-fold perovskite-type A5B5O15-δ structure, where both Fe and Ca occupy the B sites. This distinctive structure enables excellent oxygen intake/release properties below 400 °C. This oxide demonstrates the theoretical daily oxygen production rate of 2.41 mO23 kgOSM-1 at 370 °C, surpassing the performance of the previously reported material, Sr0.76Ca0.24FeO3-δ (0.81 mO23 kgOSM-1 at 550 °C). This discovery holds great potential for reducing costs and enhancing the energy efficiency in CLAS.

Correlated Rattling of Sodium-Chains Suppressing Thermal Conduction in Thermoelectric Stannides

Tin-based intermetallics with tunnel frameworks containing zigzag Na chains that excite correlated rattling impinging on the framework phonons are attractive as thermoelectric materials owing to their low lattice thermal conductivity. The correlated rattling of Na atoms in the zigzag chains and the origin of the low thermal conductivity is uncovered via experimental and computational analyses. The Na atoms behave as oscillators along the tunnel, resulting in substantial interactions between Na atoms in the chain and between the chain and framework. In these intermetallic compounds, a shorter inter-rattler distance results in lower thermal conductivity, suggesting that phonon scattering by the correlated rattling Na-chains is enhanced. These results provide new insights into the behavior of thermoelectric materials with low thermal conductivity and suggest strategies for the development of such materials that utilize the correlated rattling.

BaY16Si4O33 containing Ba(SiO4)4 orthosilicates

Single crystals of a new quaternary oxide, barium hexadecayttrium tetrasilicon tritriacontaoxide, BaY16Si4O33, were obtained from a melt-solidified sample prepared by heating a mixture of BaCO3, Y2O3, and SiO2 at 2073 K. X-ray crystal structure analysis revealed that Ba(SiO4)4 orthosilicate clusters in which a Ba atom is surrounded by four SiO4 tetrahedra were isolated in a framework composed of Y and O in the structure of BaY16Si4O33. The dielectric constant measured for polycrystalline ceramics of BaY16Si4O33 sintered at 1953 K was 13 (298 K, 1 MHz), and the thermal expansion coefficient was 8.70 × 10 −6 K−1 (298–873 K), which are close to the values previously reported for Y2O3.

Sr9La2(WO6)4 containing [WO6] octahedra

A polycrystalline sample of Sr9La2(WO6)4, nonastrontium dilanthanum tetrakis[orthotungstate(VI)], was prepared by heating a compacted powder mixture of SrCO3, WO3, and La2O3 with an Sr:La:W molar ratio of 9:2:4 at 1473 K. X-ray crystal structure analysis was performed for a Sr9La2(WO6)4 single-crystal grain grown by reheating the sample at 1673 K. Sr9La2(WO6)4 crystallizes with four formula units in the tetragonal space group I41/a and is isotypic with Sr11(ReO6)4. Two W sites with site symmetries of \overline{1} are located at the center of isolated [WO6] octahedra, and four mixed (Sr/La) sites are surrounded by eight to twelve O atoms of the [WO6] octahedra. The structure of Sr9La2(WO6)4 can be described on the basis of the double-perovskite structure with [WO6] and [(Sr/La)O x ] polyhedra alternately placed, and a vacancy (□).

Simulation of Tubular Film Extrusion of Polymer Melts

A model of the tubular film process is presented which includes power law non-linear rheological behaviour with temperature and crystallinity dependent properties. The heat transfer modelling uses an experimental correlation for the heat transfer coefficient. It is shown that except at low activation energies of viscous flow, the power law exponents have little influence on bubble shape. For activation energies of viscous flow of 11 kcal/mol and more, the temperature dependence of rheological properties dominates bubble shapes at fixed drawdown ratios, blowup ratios and frostline heights. Low activation energies of viscous flow produced wine glass shaped bubbles, while high activation energies cause rapid increases in bubble radius after the die exit.

Na3MgB37Si9: an icosahedral B12 cluster framework containing {Si8} units

Single crystals of a novel boride silicide, Na₃MgB₃₇Si₉, containing B₁₂ icosa­hedra and Si₈ units were synthesized from Na, B, Si, B₂O₃ and magnesium vapor.

Single crystals of a novel sodium–magnesium boride silicide, Na₃MgB₃₇Si₉ [a = 10.1630 (3) Å, c = 16.5742 (6) Å, space group Rm (No. 166)], were synthesized by heating a mixture of Na, Si and crystalline B with B₂O₃ flux in Mg vapor at 1373 K. The Mg atoms in the title compound are located at an inter­stitial site of the Dy_2.1B₃₇Si₉-type structure with an occupancy of 0.5. The (001) layers of B₁₂ icosa­hedra stack along the c-axis direction with shifting in the [–a/3, b/3, c/3] direction. A three-dimensional framework structure of the layers is formed via B—Si bonds and {Si₈} units of [Si]₃—Si—Si—[Si]₃.

Hydrothermal synthesis and crystal structure of a novel double-perovskite-type bismuth oxide with 3:1 ordering at the B-site

A low-temperature hydrothermal method was successfully used to synthesize a novel bismuth oxide Ba4Bi3NaO12. Here, NaBiO3·nH2O was used as one of the starting materials. Single-crystal X-ray diffraction revealed the triclinic...

Crystal structure of chain silicate Cs3LuSi3O9

A caesium lutetium(III) silicate, Cs3LuSi3O9, was synthesized by heating a pelletized mixture of Cs2CO3, Lu2O3 and SiO2 at 1273 K. Single crystals of the title compound were grown in a melted area of the pellet. Cs3LuSi3O9 is a single-chain silicate (ortho-rhom-bic space group Pna21) with a chain periodicity of six and is isostructural with Cs3 RE IIIGe3O9 (RE = Pr, Nd and Sm-Yb). The two symmetry-dependent [Si6O18]12- chains in the unit cell lie parallel to the [011] direction. The Lu3+ ions are octa-hedrally coordinated by O atoms of the silicate chains, generating a three-dimensional framework. Cs+ ions are located in the voids in the framework.

Li7Ba3Al3O11: a new supertetrahedral oxide

Colorless, transparent single crystal grains were obtained from a sample prepared by heating compacts fabricated from mixtures of Li₂O, BaO, and Al₂O₃ powders at 1093 K for 6 h under an Ar atmosphere. Single crystal X-ray diffraction analysis showed that these crystals comprised the new compound Li₇Ba₃Al₃O₁₁ having an orthorhombic cell (lattice constants: a = 13.1706(4), b = 13.1743(4), c = 13.1372(4) Å). The crystal structure of this compound is close to the cubic structure of La₃Cr_9.24N₁₁ (space group Fm3̄m) and contains eight supertetrahedra formed via the vertex-sharing of ten Li-, Li/Al-, and Al-centered oxygen tetrahedra. These supertetrahedra are arranged in the unit cell on the basis of edge-sharing. The crystal symmetry was reduced from cubic Fm3̄m to orthorhombic Pnnn as a result of the partial ordering of Li and Al atoms in the oxygen tetrahedra with various Li/Al site occupancies from 0.0/1.0 to 1.0/0.0. Polycrystalline samples of Li₇Ba₃Al₃O₁₁ were synthesized by heating a mixture of starting materials in the molar ratio corresponding to the stoichiometric composition of Li₇Ba₃Al₃O₁₁ at 1073 K for 6 h under Ar. The electrical conductivity of a polycrystalline sample was determined using the direct current two-terminal method with Li electrodes to be 1.3 × 10^-8 S cm^-1 at 553 K. The estimated activation energy in the range of 553-673 K was 0.88 eV.

Ba33Zn22Al8O67 with a Framework of ([O(Zn/Al)4]/Ba)(Zn/AlO4)4 Motifs

Single crystals of a new oxide, Ba₃₃Zn₂₂Al₈O₆₇ (melting point = 1452 K), were grown in a melt-solidified sample prepared by heating a compact of a BaCO₃, ZnO, and Al₂O₃ mixed powder in a dry airflow. Ba₃₃Zn₂₂Al₈O₆₇ can be handled in dry air, but it decomposes into carbonates, hydroxides, and hydrates in humid air. Single-crystal X-ray structure analysis clarified that Ba₃₃Zn₂₂Al₈O₆₇ crystallizes in a cubic cell (a = 16.3328 (3) Å, space group F23) having a three-dimensional Zn/AlO₄ framework in which {([OZn₄]/Ba)(Zn/AlO₄)₄} motifs are connected to each other by bridging Zn/AlO₄ tetrahedra. A Ba atom or a [OZn₄] cluster is statistically situated at the center of the motif with a probability of 0.5. Motifs of another type, {([O(Zn/Al)₄])(Zn/AlO₄)₄}, are isolated from the Zn/AlO₄ framework. These motifs, {([OZn₄]/Ba)(Zn/AlO₄)₄} and {([O(Zn/Al)₄])(Zn/AlO₄)₄}, are alternatingly arranged along the a axis like a checkered cube, and Ba atoms are situated between the motifs. A linear thermal expansion coefficient of 10.4 × 10^-6 K^-1 was measured in an Ar gas flow at 301-873 K for a sintered Ba₃₃Zn₂₂Al₈O₆₇ polycrystalline sample with a relative density of 73%. A relative permittivity of 31 and a temperature coefficient of 15 ppm K^-1 at 301 K were obtained for another sintered sample (relative density = 70%) in a dry airflow. The electrical conductivity at 1073 K and the activation energy for conduction at 923-1073 K measured for the sintered samples in dry and wet airflows were 6.2 × 10^-7 S cm^-1 and 0.65 eV and 2.9 × 10^-6 S cm^-1 and 0.59 eV, respectively.

A novel ternary bismuthide, NaMgBi: crystal and electronic structure and electrical properties

A new ternary sodium magnesium bismuthide, NaMgBi, has been synthesized from the constituent metals, and its crystal structure was determined by single-crystal X-ray diffraction. NaMgBi crystallizes in a tetragonal PbFCl-type structure corresponding to the space group P4/nmm, where Z = 2, a = 4.7123(4) and c = 7.8158(7) Å. The structure is composed of layers formed by edge-sharing Bi tetrahedra centered with Mg stacked in the c-axis direction, and these layers sandwich the Na atoms. First-principles computations based on density functional theory calculations have verified that the most stable atomic configuration is the one in which the Na and Mg atoms occupy the 2a and 2c sites, respectively. The electrical resistivity measured for a sintered polycrystalline sample of NaMgBi with a relative density of 70% was found to gradually decrease from 868 to 26.4 mΩ cm upon increasing the temperature from 297 to 506 K, and the Seebeck coefficient decreased from 273 to 180 μV K−1 upon increasing the temperature from 298 to 496 K. Electronic structure calculations have revealed that NaMgBi must be a semiconductor with a small band gap of ∼0.1 eV.

Sr7N2Sn3: a layered antiperovskite-type nitride stannide containing zigzag chains of Sn4 polyanions

Metallic black platelet single crystals of a new ternary compound, Sr7N2Sn3, were obtained by heating Sr and Sn in a Na flux together with NaN3 as a nitrogen source at 1073 K, followed by slow cooling. Single-crystal X-ray analysis revealed that this compound crystallizes in an orthorhombic cell with the cell parameters a = 10.4082(2), b = 18.0737(4), and c = 7.43390(10) Å (space group Pmna, Z = 2), and has a layered (modular) antiperovskite-type structure which could be related to the inverse structure of Ca2Nb2O7 ((Ca2)[Ca2Nb4O14]). Four-membered zigzag [Sn4] chains are situated between slabs comprising four antiperovskite layers cut by the (110) plane of the ideal anitiperovskite structure, and Sr7N2Sn3 can be expressed as [Sn4][Sn2N4Sr14]. Although an electron-precise valence electron distribution according to the formula (Sr2+)14(N3−)4(Sn4−)2([Sn4]8−) is proposed for this ternary compound, yet, there are certain structural peculiarities which cannot be explained by this idealized picture. Therefore, first principles-based means were employed to account for the aforementioned structural features.

Crystal structure of silver carbonate iodide Ag10(CO3)3I4

The new silver carbonate iodide, Ag₁₀(CO₃)₃I₄, comprises layers of I atoms, Ag atoms, and CO₃ groups stacked along [10].

The title silver carbonate iodide, Ag₁₀(CO₃)₃I₄, deca­silver(I) tris­(carbonate) tetra­iodide, was recently reported as a precursor of the new superionic conductor Ag₁₇(CO₃)₃I₁₁. Ag₁₀(CO₃)₃I₄, was prepared by heating a stoichiometric powder mixture of AgI and Ag₂CO₃ at 430 K. A single-crystal suitable for X-ray diffraction analysis was obtained by slow cooling of a melt with an AgI-rich composition down from 453 K. Ag₁₀(CO₃)₃I₄ exhibits a layered crystal structure packed along [10], in which Ag atoms are inter­calated between the layers of hexa­gonally close-packed I atoms, and CO₃ groups. Up to now, Cs₃Pb₂(CO₃)₃I is the only other compound containing carbonate groups and iodide ions registered in the Inorganic Crystal Structure Database.

Hydrothermal Synthesis and Crystal Structure of a Novel Bismuth Oxide: (K0.2Sr0.8)(Na0.01Ca0.25Bi0.74)O3

A novel distorted perovskite-type (K_0.2Sr_0.8)(Na_0.01Ca_0.25Bi_0.74)O₃ was prepared by a hydrothermal method using the starting materials NaBiO₃·nH₂O, Sr(OH)₂·8H₂O, Ca(OH)₂, and KOH. Single-crystal X-ray diffraction of the novel compound revealed a GdFeO₃-related structure belonging to the monoclinic system of the space group Cc with the following cell parameters: a = 11.8927 (17) Å, b = 11.8962 (15) Å, c = 8.4002 (10) Å, and β = 90.116 (9)°. The final R-factors were obtained as R ₁ = 0.0354 and wR ₂ = 0.0880 (using all the data). K⁺ and Sr²⁺ ions were distributed at four types of A-sites. On the other hand, four Bi⁵⁺-sites (Bi1, Bi2, Bi3, and Bi4) were occupied by four Ca²⁺ ions (Ca1, Ca2, Ca3, and Ca4), and the first three B-sites were occupied predominantly by Bi⁵⁺ with Na⁺ ions. The forth B-site was occupied predominantly by the Ca²⁺ ion with Bi⁵⁺ ions. Two types of B-sites, thus forming tilted distorted (Na/Ca/Bi)O₆ and (Bi/Ca)O₆ octahedra, have an ordering of 3:1 represented as (K/Sr)₄(Na/Ca/Bi)₃(Bi/Ca)O₁₂. The distorted (Na/Ca/Bi)O₆ and (Ca/Bi)O₆ octahedra formed a perovskite-type network by corner sharing with features closely matching those of a GdFeO₃-type structure. The novel compound is the first example of a perovskite-type bismuth oxide containing only Bi⁵⁺ in a system without a Ba atom and has a unique ordering (3:1) of the B site. The compound showed photocatalytic activity for phenol degradation under visible light irradiation.

Superionic Ag+ Conductor Ag17(CO3)3I11

A new superionic Ag⁺ conductor with a nominal composition Ag₁₇(CO₃)₃I₁₁ (11AgI-3Ag₂CO₃) was found in the AgI-Ag₂CO₃ system. The conductor, which was formed at temperatures from 100 to 170 °C, is a metastable phase that gradually decomposes into AgI and Ag₁₀(CO₃)I₄ over a period of a few weeks at room temperature (RT). A Ag⁺ ionic conductivity of 0.16 S/cm was measured at RT, and an activation energy of 0.33 eV was evaluated in the temperature range from -9 to 19 °C. Single-crystal X-ray analysis revealed that Ag₁₇(CO₃)₃I₁₁ crystallized in a rhombohedral unit cell with hexagonal parameters of a = 15.8831(6) Å and c = 30.0730(13) Å at -183 °C and space group R3c. The Ag atoms were distributed over 53 sites in the asymmetry unit, with a maximum occupancy of 0.33(8). The continuous distribution of the partially occupied Ag sites was associated with the conduction paths of the Ag⁺ ions in the structure.

Lu-atom-ordered oxonitridoaluminosilicate Ba0.9Ce0.1LuAl0.2Si3.8N6.9O0.1

A single crystal of Ba_0.9Ce_0.1LuAl_0.2Si_3.8N_6.9O_0.1 (barium cerium lutetium aluminosilicate nitride oxide) was obtained by heating a mixed powder of Ba₃N₂, Si₃N₄, Al, Lu₂O₃, and CeO₂ at 2173 K for 1 h under N₂ gas at 0.85 MPa. X-ray single-crystal structure analysis revealed that the title oxynitride is hexa­gonal and isostructural with BaYbSi₄N₇. (Ba,Ce) and Lu atoms occupy twelvefold and sixfold coordination sites, respectively.

A single crystal of Ba_0.9Ce_0.1LuAl_0.2Si_3.8N_6.9O_0.1 (barium cerium lutetium aluminosilicate nitride oxide) was obtained by heating a mixed powder of Ba₃N₂, Si₃N₄, Al, Lu₂O₃, and CeO₂ at 2173 K for 1 h under N₂ gas at 0.85 MPa. X-ray single-crystal structure analysis revealed that the title oxynitride is hexa­gonal (lattice constants: a = 6.0378 (5) Å, c = 9.8133 (9) Å; space group: P6₃mc) and isostructural with BaYbSi₄N₇. (Ba,Ce) and Lu atoms occupy twelvefold and sixfold coordination sites, respectively.

Crystal structure of lutetium aluminate (LUAM), Lu4Al2O9

Single-crystal X-ray structure analysis revealed that Lu₄Al₂O₉ is isostructural with Eu₄Al₂O₉ and contains Lu atoms in six- and sevenfold coordination, together with tetra­hedral Al atoms.

The crystal structure of the title compound containing lutetium, the last element in the lanthanide series, was determined using a single crystal prepared by heating a pressed pellet of a 2:1 molar ratio mixture of Lu₂O₃ and Al₂O₃ powders in an Ar atmosphere at 2173 K for 4 h. Lu₄Al₂O₉ is isostructural with Eu₄Al₂O₉ and composed of Al₂O₇ di­tetra­hedra and Lu-centered six- and sevenfold oxygen polyhedra. The unit-cell volume, 787.3 (3) ų, is the smallest among the volumes of the rare-earth (RE) aluminates, RE₄Al₂O₉. The crystal studied was refined as a two-component pseudo-merohedric twin.

Hydrothermal Synthesis and Crystal Structure of a Mixed-Valence Bismuthate, Na3Bi3O8

Four types of bismuth oxides, Na₃Bi₃O₈, NaBiO₃, α-Bi₂O₃, and ε-Bi₂O₃, were obtained by hydrothermal reactions using NaBiO₃·nH₂O in NaOH solution. The crystal structure of a new phase (Na₃ Bi³⁺)Bi₂⁵⁺O₈ ((Na_0.75Bi_0.25)₂BiO₄) was determined by using single crystal X-ray diffraction data, and this compound was found to show a Na₂MnCl₄-related structure with a monoclinic system (space group, Pm) with the following lattice parameters: a = 5.990 (2) Å, b = 3.335 (2) Å, c = 10.108 (2) Å, and β = 91.08 (3)°. The final R-factors R₁ and wR₂ were 0.041 and 0.090 (all data), respectively. The new phase was composed of mixed valence states of Bi (Bi³⁺ and Bi⁵⁺, with a mean Bi valence of 4.30) with five distinct Bi sites, where two Bi⁵⁺ (Bi1 and Bi2) fully occupied the distorted octahedral sites and three Bi³⁺ (Bi3, Bi4, and Bi5) were statistically distributed at the split sites with Na⁺ (Na3, Na4, and Na5). The Na6 site is fully occupied. The distorted Bi⁵⁺O₆ octahedra formed one-dimensional chains via edge-sharing along the b-axis, with the chains held by Bi³⁺/Na⁺ split sites. The structural feature except for the split distribution of Bi³⁺/Na⁺ was classified as a Na₂MnCl₄-type structure. DFT calculations based on a model discounting the split distribution of Bi³⁺/Na⁺ indicated that Bi 6s and O 2p orbitals form sp hybridization at the conduction band. This new mixed valence bismuth oxide exhibited photocatalytic activity for phenol degradation under visible light irradiation. In addition to Na₃Bi₃O₈, the hydrothermal reaction using NaBiO₃·nH₂O in NaOH solution yielded micrometer-sized single crystals of an ilmenite-type NaBiO₃ and two polymorphs of bismuth oxides with monoclinic (α-Bi₂O₃) and orthorhombic (ε-Bi₂O₃) structures, depending on the reaction temperature and NaOH concentration.

Synthesis, Crystal Structure, and Luminescence Properties of a White-Light-Emitting Nitride Phosphor, Ca0.99Eu0.01AlSi4N7

Colorless transparent single crystals of a new europium-doped calcium aluminum silicon nitride, Ca_0.99Eu_0.01AlSi₄N₇, were synthesized by heating a mixture of binary nitrides (Ca₃N₂, EuN, AlN, Si₃N₄, and Mg₃N₂) at 2150 °C under a nitrogen gas pressure of 0.85 MPa. The X-ray diffraction reflections from a single crystal were indexed with orthorhombic cell parameters a = 11.6819(3) Å, b = 21.0193(6) Å, and c = 4.91770(10) Å. The crystal structure was isomorphic to that of SrAlSi₄N₇:Eu (space group Pna2₁). One of the Ca/Eu sites was split into two sites of 4-fold and 8-fold nitrogen coordination. A white-light emission spectrum with two peaks at wavelengths of 498 and 614 nm was observed from the single crystals under 400 nm near-ultraviolet-light irradiation. The CIE1931 chromaticity of the white light was plotted at x = 0.378 and y = 0.429; the mean color-rendering index Ra was 81.

Na3Pt10Si5: A Non-Centrosymmetric Superconductor Having Rattling Na Atoms in the Tunnel Framework Structure

Single crystals of a novel Na-Pt-Si ternary compound, Na₃Pt₁₀Si₅, were synthesized by heating the constituent elements at 1423 K. It crystallizes in a non-centrosymmetric trigonal structure of space group R32 (Z = 3) with lattice constants of a = 10.1536(3) Å and c = 10.1539(3) Å at 300 K. The structure consists of a three-dimensional framework made of Pt and Si atoms, and the Na atoms are contained in the tunnels of the framework. The large magnitude and the temperature dependence of the atomic displacement parameter of the Na site reveal a large thermal vibration indicative of a "rattling" motion of Na atoms in the oversized tunnel. The electronic structure calculations explain the observed metallic properties on the basis of the covalent bonds between the Pt and Si atoms in the framework and the ionic bonding of the Na atoms to the framework. A type II superconductivity with a transition temperature of 2.9 K and an upper critical field of 2.5 kOe are observed for a polycrystalline sintered bulk sample of Na₃Pt₁₀Si₅ prepared by heating at 1353 K in Na vapor. Heat capacity measurements reveal a strong coupling superconductivity that is probably caused by an electron-phonon interaction enhanced by the rattling motion of the Na atoms.

α-SrZn5-Type solid solution, BaZn2.6Cu2.4

BaCu_2.6Zn_2.4 has an α-SrZn₅-type structure. Although the Ba atom is larger than the Sr atom, the cell volume of title compound is smaller than that of α-SrZn₅. This can be attributed to the partial substitution of Cu atoms with Zn atoms, and the average Ba—Zn/Cu distance becomes shorter than the Sr—Zn distance.

Single crystals of the title compound barium zinc copper, BaCu_2.6Zn_2.4, were obtained from a sample prepared by heating metal chips of Ba, Cu, and Zn in an Ar atmosphere up to 973 K, followed by slow cooling. Single-crystal X-ray structure analysis revealed that BaCu_2.6Zn_2.4 crystallizes in an ortho­rhom­bic cell [a = 12.9858 (3), b = 5.2162 (1), and c = 6.6804 (2) Å] with an α-SrZn₅-type structure (space group Pnma). The three-dimensional framework consists of Cu and Zn atoms, with Ba atoms in the tunnels extending in the b-axis direction. Although the Ba atom is larger than the Sr atom, the cell volume of BaCu_2.6Zn_2.4 [452.507 (19) ų] is smaller than that of α-SrZn₅ [466.08 ų]. This decrease in volume can be attributed to the partial substitution of Cu atoms by Zn atoms in the framework because the Cu—Zn and Cu—Cu bonds are shorter than the Zn—Zn bond. The increase in Ba—Zn inter­atomic distances from the Sr—Zn distances is cancelled out by the partial replacement of Zn with Cu atoms, which leads to shorter average Ba—Zn/Cu distances.

Hydrothermal Synthesis and Crystal Structure of a (Ba0.54K0.46)4Bi4O12 Double-Perovskite Superconductor with Onset of the Transition Tc ∼ 30 K

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.

Synthesis, crystal structure and properties of a quaternary oxide with a new structure type, BiGaTi4O11

A new quaternary oxide, BiGaTi₄O₁₁ (bismuth gallium tetratitanium undecaoxide), was prepared by heating a mixture of the binary oxides at 1373 K in air. BiGaTi₄O₁₁ melts at 1487 K and prismatic single crystals were obtained from a sample melted at 1523 K and solidified by furnace cooling. The structure of BiGaTi₄O₁₁ was analyzed using single-crystal X-ray diffraction to be of a new type that crystallized in the space group Cmcm. A Bi³⁺ site is coordinated by nine O^2- anions, and three oxygen-coordinated octahedral sites are statistically occupied by Ga³⁺ and Ti⁴⁺ cations. A relative dielectric constant of 46 with a temperature coefficient of 57 ppm K^-1 in the temperature range 297-448 K was measured for a polycrystalline ceramic sample at 150 Hz-1 MHz with a dielectric loss tan δ of less than 0.01. Electrical resistivities measured at 1073 K by alternating-current impedance spectroscopic and direct-current methods were 1.16 × 10^-4 and 1.14 × 10^-4 S cm^-1, respectively, which indicates that electrons and/or holes were conduction carriers at high temperature. The optical band gap estimated by the results of diffuse reflectance analysis was 2.9-3.0 eV, while the band gap obtained from the activation energy for electrical conduction was 3.5 eV.

Single crystal growth and structure analysis of type-I (Na/Sr)-(Ga/Si) quaternary clathrates

Single crystals of (Na/Sr)-(Ga/Si) quaternary type-I clathrates, Na8-y Sr y Ga x Si46-x , were synthesized by evaporating Na from a mixture of Na-Sr-Ga-Si-Sn in a 6 : 0.5 : 1 : 2 : 1 molar ratio at 773 K for 12 h in an Ar atmosphere. Electron-probe microanalysis and single-crystal X-ray diffraction revealed that three crystals from the same product were Na8-y Sr y Ga x Si46-x with x and y values of 7.6, 2.96; 8.4, 3.80; and 9.1, 4.08. It was also shown that increasing the Sr and Ga contents increased the electrical resistivity of the crystal from 0.34 to 1.05 mΩ cm at 300 K.

Na-Ga-Si type-I clathrate single crystals grown via Na evaporation using Na-Ga and Na-Ga-Sn fluxes

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_5.70Si_40.30, of size 2.9 mm were grown via the evaporation of Na from a Na–Ga–Si melt with the molar ratio of Na : Ga : Si = 4 : 1 : 2 at 773 K for 21 h under an Ar atmosphere. The crystal structure was analyzed using X-ray diffraction with the model of the type-I clathrate (cubic, a = 10.3266(2) Å, space group Pm3̄n, no. 223). By adding Sn to a Na–Ga–Si melt (Na : Ga : Si : Sn = 6 : 1 : 2 : 1), single crystals of Na₈Ga_xSi_46−x (x = 4.94–5.52, a = 10.3020(2)–10.3210(3) Å), with the maximum size of 3.7 mm, were obtained via Na evaporation at 723–873 K. The electrical resistivities of Na₈Ga_5.70Si_40.30 and Na₈Ga_4.94Si_41.06 were 1.40 and 0.72 mΩ cm, respectively, at 300 K, and metallic temperature dependences of the resistivities were observed. In the Si L_2,3 soft X-ray emission spectrum of Na₈Ga_5.70Si_40.30, a weak peak originating from the lowest conduction band in the undoped Si₄₆ was observed at an emission energy of 98 eV.

Single crystals of a Na–Ga–Si clathrate, Na₈Ga_4.94Si_41.06, of size 3.7 mm were grown via the evaporation of Na from a Na–Ga–Si–Sn melt with the molar ratio of Na : Ga : Si : Sn = 6 : 1 : 2 : 1 at 873 K for 3 h under an Ar atmosphere.

Crystal structure of Ti8Bi9O0.25 containing inter-stitial oxygen atoms

Single crystals of Ti8Bi9O0.25, titanium bis-muth oxide (8/9/0.25), were obtained from a sample prepared by heating a mixture of Ti, TiO2 and Bi powders in an Ar atmosphere. Single-crystal X-ray analysis revealed that the introduction of O atoms into the structure of Ti8Bi9 retains the space-group type P4/nmm. The oxygen site is located within a Ti4 tetra-hedron (point group symmetry m2) that is vacant in the Ti8Bi9 crystal structure. The occupancy of this site is 0.25 (4), and the O-Ti distance is 1.8824 (11) Å.

Ternary Suboxides Ti7Ga2O6, Ti3GaO, and Ti5Ga3O

Single crystals of the new suboxides Ti₇Ga₂O₆ and Ti₃GaO were prepared using a Bi flux. Ti₇Ga₂O₆ has a novel monoclinic crystal structure ( a = 17.3111(8) Å, b = 2.97660(10) Å, c = 7.2563(3) Å, β = 105.836(2)°, space group C2/ m), in which three O sites and one Ga site are separately coordinated by Ti atoms. Ti₃GaO crystallizes in an orthorhombic cell ( a = 3.0952(2) Å, b = 10.6440(7) Å, c = 8.3206(5) Å, space group Cmcm) with a filled-Re₃B type (anti-CaIrO₃ type or antipost-perovskite type) structure. The electrical resistivities of a single crystal of Ti₃GaO as measured in the c-axis direction were 1.6 × 10^-6 Ωm at 300 K and 0.15 × 10^-6 Ωm at 10 K. Single crystals of Ti₅Ga₃O _x ( x = 1) with a filled-Mn₅Si₃ type structure (hexagonal, a = 7.5882(2) Å, c = 5.30170(10) Å, space group P6₃/ mcm) were also obtained.

Single crystals of the filled Ti2N-type η-phase Ti3Zn3Ox (x = 1.07 and 1.23) prepared using a Bi flux

Single crystals of the filled Ti₂Ni-type Ti₃Zn₃O_x η-phase (cubic, space group Fd-3m) having {111} facets were obtained by heating Ti, Zn and ZnO with a Bi flux. The lattice parameter of a single crystal prepared at 800°C was 11.4990 (2) Å, which is close to that of Ti₃Zn₃O_∼0.5 (a = 11.502 Å), as reported by Rogl & Nowotny [Monatsh. Chem. (1977), 108, 1167-1180]. The occupancies of the O1 (16c) and O2 (8a) sites were 1 and 0.071 (12), respectively, and the composition of the crystal was determined to be Ti₃Zn₃O_1.04. A single crystal from the sample prepared at 650°C had the same structure type, with a lattice parameter of 11.5286 (2) Å. However, O atoms were situated at a new 32e site in addition to the original 16c and 8a sites, and the Zn-atom positions were split in accordance with the new O-atom site. The chemical formula Ti₃Zn₃O_1.27 determined by X-ray diffraction occupancy refinement agreed with the chemical composition obtained for the cross section of the single crystal determined with an electron probe microanalyzer.

Synthesis, Crystal Structure, and Photoluminescence of the Boron-Aluminum-Silicon Nitride Phosphor Sr3BAl5Si9N20:Eu

Single crystals of new boron-aluminum-silicon nitrides, Sr₃BAl₅Si₉N₂₀ and Sr_2.91Eu_0.09BAl₅Si₉N₂₀, were synthesized by heating binary nitride mixtures at 2030 °C under a N₂ pressure of 0.85 MPa. The X-ray diffraction spots from single crystals of these two compounds were indexed with the trigonal cell parameters a = 22.7406(8) Å, c = 5.7066(2) Å and a = 22.7439(8) Å, c = 5.7050(2) Å, respectively, and the crystal structures were determined to have the space group P3 c1, with B atoms situated at planar 3-fold-coordinated N sites. A three-dimensional framework structure is constructed for these materials based on the sharing of N atoms of Al/Si-N₄ tetrahedra and B-N₃ triangles. In this framework, Sr/Eu atoms are located at three sites, surrounded by 10 N atoms. Single crystals of Sr_2.91Eu_0.09BAl₅Si₉N₂₀ emitted yellow light with a peak wavelength of 565 nm and a full width at half-maximum of 106 nm under 450 nm light irradiation. The emission intensity of these crystals at 200 °C was found to be 12% of the intensity at 25 °C.

Soft X-ray emission spectroscopy study of electronic structure of sodium borosilicide Na8B74.5Si17.5

Chemical bonding state of sodium borosilicide Na8B74.5Si17.5, which is a new member of B12-cluster materials, is investigated by soft X-ray emission spectroscopy. The material is composed of B12 cluster network and characteristic silicon chains of [-Si-(Si-Si)3-Si-] connected by sp3 bonding, in which bonding distances and bonding angles are close to those in cubic Si crystal. B K-emission spectrum of the material showed a similar but a broader intensity distribution with those of B12 cluster materials of α-r-B, B4C and β-r-B. The broader intensity distribution can be due to a variation of B-B bond length in B12 cluster. The density of states (DOS) of silicon chains of [-Si-(Si-Si)3-Si-] was experimentally derived. It shows a similar energy width, and peak or shoulder structures in intensity distribution with those of L-emission spectrum of cubic Si. From comparisons between experimental spectra and corresponding calculated DOS, covalent bonding between Si chain and B12 cluster network is suggested. Those are discussed by using a theoretically calculated density of state of Na8B74.5Si17.5 by using WIEN2k code.

Synthesis and Crystal Structure of Suboxide Solid Solutions, Ti12-δGaxBi3-xO10

Single crystals of suboxide solid solutions Ti_12-δGa_xBi_3-xO₁₀ (x = 1.42-1.74; δ = 0.77-0.62) were prepared at 900 °C with a Bi flux. Crystal structure analysis by X-ray diffraction (XRD) revealed that the solid solutions are isostructural with Ti_12-δSn₃O₁₀ (cubic, space group Fm3̅m). The cell parameter a decreases from 13.5616(3) to 13.5402(5) Å with increasing Ga content, x, while the total valence electron number of Ti_12-δGa_xBi_3-xO₁₀ is maintained at 117.1 by decreasing Ti defects, δ. Stella octangula is formed by sharing of the edges of four supertetrahedra composed of O-centered Ti tetrahedra and trigonal bipyramids (oxide part). Another superpolyhedron is formed by sharing of the pyramidal planes of Ga/Bi-centered, Ti-monocapped square antiprisms (intermetallic part). These two parts are incorporated in the structure. A polycrystalline bulk of a solid solution with x = 2.01 and δ = 0.67 [a = 13.53772(13) Å] was synthesized by reaction sintering at 950 °C from a mixture of Ti, TiO₂, Bi₂O₃, and Ga₂O₃. The resistivities measured for the bulk were (2.2-2.4) × 10^-5 Ω m in the temperature range from 10 to 300 K.

Electronic structure of AlCrN films investigated using various photoelectron spectroscopies and ab initio calculations

The valence band (VB) structures of wurtzite AlCrN (Cr concentration: 0-17.1%), which show optical absorption in the ultraviolet-visible-infrared light region, were investigated via photoelectron yield spectroscopy (PYS), x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS), and ab initio density of states (DOS) calculations. An obvious photoelectron emission threshold was observed ~5.3 eV from the vacuum level for AlCrN, whereas no emission was observed for AlN in the PYS spectra. Comparisons of XPS and UPS VB spectra and the calculated DOS imply that Cr 3d states are formed both at the top of the VB and in the AlN gap. These data suggest that Cr doping could be a viable option to produce new materials with relevant energy band structures for solar photoelectric conversion.

Crystal structure of TiBi2

Black granular single crystals of monotitanium dibismuth, TiBi₂, were synthesized by slow cooling of a mixture of Bi and Ti from 693 K. The title compound is isostructural with CuMg₂ (ortho-rhom-bic Fddd symmetry). Ti atoms are located in square anti-prisms of Bi atoms. The network of one type of Bi atom spirals along the a-axis direction while honeycomb layers of the other type of Bi atom spreading in the ab plane inter-lace one another.

Synthesis and crystal structures of BaLaSi2 with cis-trans Si chains and Ba5LaSi6 with pentagonal Si rings

Prismatic single crystals of novel compounds BaLaSi2 and Ba5LaSi6 were synthesized from the elements with or without a Na flux. The crystal structures of the compounds were analyzed by X-ray diffraction. BaLaSi2, containing cis–trans ∞1[Si] chains, crystallizes in an orthorhombic cell (a = 4.6414(2) Å, b = 14.8851(7) Å, c = 6.7519(5) Å; space group, Cmcm (No. 63), Z = 4) and is isotypic with the low-temperature phase of LaSi. The crystal structure of Ba5LaSi6 (a = 17.1447(5) Å, b = 4.8767(1) Å, and c = 17.9102(4) Å; space group Pnma (No. 62), Z = 4) is a new type containing isolated anionic groups (0[Si5–Si]) of a pentagonal Si ring with a Si–Si stem. The electrical resistivities measured for the polycrystalline BaLaSi2 and Ba5LaSi6 sintered samples were 0.31 and 0.48 mΩ·cm, respectively, at 300 K and increased with temperature. The Seebeck coefficients of BaLaSi2 and Ba5LaSi6 were −7.6 and −11 μV·K–1, respectively, at 296 K.

A thermoelectric zintl phase Na2+x Ga2+x Sn4-x with disordered Na atoms in helical tunnels

A polycrystalline sample of Na2+x Ga2+x Sn4-x with x = 0.19 has low thermal conductivities of 0.56 and 0.58 W m(-1) K(-1) due to static and dynamic positional disorder of Na atoms in the crystal structure and dimensionless figures of merit (ZT values) values of 0.98 and 1.28 at 295 and 340 K, respectively. The performance is comparable to those of commercial Bi2 Te3 -based materials.

Li-rich Li-Si alloy as a lithium-containing negative electrode material towards high energy lithium-ion batteries

Lithium-ion batteries (LIBs) are generally constructed by lithium-including positive electrode materials, such as LiCoO₂, and lithium-free negative electrode materials, such as graphite. Recently, lithium-free positive electrode materials, such as sulfur, are gathering great attention from their very high capacities, thereby significantly increasing the energy density of LIBs. Though the lithium-free materials need to be combined with lithium-containing negative electrode materials, the latter has not been well developed yet. In this work, the feasibility of Li-rich Li-Si alloy is examined as a lithium-containing negative electrode material. Li-rich Li-Si alloy is prepared by the melt-solidification of Li and Si metals with the composition of Li₂₁Si₅. By repeating delithiation/lithiation cycles, Li-Si particles turn into porous structure, whereas the original particle size remains unchanged. Since Li-Si is free from severe constriction/expansion upon delithiation/lithiation, it shows much better cyclability than Si. The feasibility of the Li-Si alloy is further examined by constructing a full-cell together with a lithium-free positive electrode. Though Li-Si alloy is too active to be mixed with binder polymers, the coating with carbon-black powder by physical mixing is found to prevent the undesirable reactions of Li-Si alloy with binder polymers, and thus enables the construction of a more practical electrochemical cell.