A2B′B″O6 perovskites: A review

Probing the structural, mechanical, phonon, thermal, and transport properties of magnetic halide perovskites XTiBr3 (X = Rb, Cs) through ab-initio results

Herein, we have first reported the intrinsic properties, including structural, mechanical, electronic, magnetic, thermal, and transport properties of XTiBr₃ (X = Rb, Cs) halide perovskites within the simulation scheme of density functional theory as integrated into Wien2k. First and foremost, the structural stability in terms of their ground state energies has been keenly evaluated from their corresponding structural optimizations, which advocate that XTiBr₃ (X = Rb, Cs) has a stable ferromagnetic rather than the competing non-magnetic phase. Later on, the electronic properties have been computed within the mix of two applied potential schemes like Generalized Gradient Approximation (GGA) along with Trans-Bhala modified Becke Johnson (TB-mBJ), which thoroughly addresses the half-metallic behaviour with spin-up as metallic and in contrast to opposite spin-down channel signatures the semiconducting behaviour. Furthermore, the spin-splitting seen from their corresponding spin-polarised band structures offers a net magnetism of 2 µB which lends their opportunities to unlock the application branch of spintronics. In addition, these alloys have been characterised to show their mechanical stability describing the ductile feature. Moreover, phonon dispersions decisively certify the dynamical stability within the density functional perturbation theory (DFPT) context. Finally, the transport and thermal properties predicted within their specified packages have also been forwarded in this report.

Gradient Strain-Induced Room-Temperature Ferroelectricity in Magnetic Double-Perovskite Superlattices

Single-phase multiferroics suffer from a fundamental contradiction between polarity and magnetism in d⁰ electronic configuration, motivating studies of unconventional ferroelectricity in magnetic oxides. However, low critical temperature and polarization still need to be overcome. Here, it is reported that the switchable polarization behavior at room temperature in [(La₂ NiMnO₆ )/(La₂ CoMnO₆ )]_n double-perovskite magnetic superlattice films is achieved by engineering a microstructure with gradient strains, and the ferromagnetic Curie temperature did not show a rapid decrease. The synergy of gradient strains and superlattice components plays a decisive role in inducing ferroelectricity via the tilting or rotation of various oxygen octahedra. Such distortion responses to gradient strains are accompanied by slight magnetic fluctuations, maximizing the preservation of the initial magnetic exchange interactions, which alleviates the contradiction of multiferroic coexistence to a certain extent. This work confirms the room-temperature ferroelectricity in double-perovskite superlattices and provides a preferred strategy for confronting the difficulty of multiferroic coexistence in single-phase materials.

CaFeFeNbO6 - an iron-based double double perovskite

Ordering of cations is important for controlling properties of ABO₃ perovskites, and CaFeFeNbO₆ is the first example of an Fe-based AA'BB'O₆ double double perovskite, with Ca²⁺/Fe²⁺ ordered on A-site columns, and Fe³⁺/Nb⁵⁺ at the octahedral B-sites. Substantial (37%) antisite disorder of the latter cations leads to spin glassy magnetism below a freezing transition at 12 K. The CaMnFeNbO₆ analogue also shows substantial cation disorder and spin glassy behaviour. Comparison of synthesis pressures for ordered materials based on different A-site transition metals, suggests that pressures of at least 14-18 GPa will be required to discover the expected plethora of double double perovskites based on A' cations smaller than Mn²⁺.

B-site order/disorder in A2BB'O6and its correlation with their magnetic property

The disorder in any system affects their physical behavior. In this scenario, we report the possibility of disorder in A₂BB'O₆oxides and their effect on different magnetic properties. These systems show anti-site disorder by interchanging B and B' elements from their ordered position and giving rise to an anti-phase boundary. The presence of disorder leads to a reduction in saturationMand magnetic transition temperature. The disorder prevents the system from sharp magnetic transition which originates short-range clustered phase (or Griffiths phase) in the paramagnetic region just above the long-range magnetic transition temperature. Further, we report that the presence of anti-site disorder and anti-phase boundary in A₂BB'O₆oxides give different interesting magnetic phases like metamagnetic transition, spin-glass, exchange bias, magnetocaloric effect, magnetodielectric, magnetoresistance, spin-phonon coupling, etc.

Magnetocaloric effect and Griffiths phase analysis in a nanocrystalline Ho2NiMnO6 and Ho2CoMnO6 double perovskite

Rare-earth double perovskite oxides have intriguing magnetocaloric properties at cryogenic temperatures. In this study, Ho₂NiMnO₆ and Ho₂CoMnO₆ were synthesized using the sol-gel method, which crystallized in a monoclinic structure in the P2₁/n space group. The magnetic phase transition was observed at 81.2 K for Ho₂NiMnO₆ and 73.5 K for Ho₂CoMnO₆. The presence of a paramagnetic matrix and short-range ferromagnetic clusters causes magnetic disorder in these double perovskites, resulting in Griffiths phase formation. The Arrott plot confirms that compounds undergo second-order phase transition. At an applied magnetic field of 5 T, the maximum magnetic entropy change (-ΔS) for the studied compounds is 1.7 and 2.2 J kg^-1 K^-1, respectively. The transition metals Ni and Co in a double perovskite cause lattice distortion in the structural parameters and oxidation states of manganese (Mn³⁺/Mn⁴⁺), which changes the magnetic and magnetocaloric properties. The quantitative approach provides a systematic study of magnetocaloric properties of the rare earth double perovskite compounds with ferromagnetic 3d transition elements.

A combined study on structural, magnetic and specific heat on double perovskite iridates Ln2CoIrO6[Ln = Pr, Nd]

We report rich magnetic behavior for Co-Ir based double perovskites consisting of different rare earth cations Pr and Nd: Pr₂CoIrO₆(PCIO) and Nd₂CoIrO₆(NCIO). Both oxides show an antisite disorder of 10% and a ferrimagnetic transition,TFiMaround 96 K and 98 K respectively. The long range magnetic ordering is arising from the canted antiferromagnetic ordering between the Co²⁺and Ir⁴⁺ions. A prominent peak around 27 K in magnetization data of NCIO indicates that the total moment of Nd ion is antiferromagnetically coupled to the Co-Ir sublattice. The long range order of the Nd sublattice is corroborated by the evidence of an anomaly in specific heat at very low temperature. The compounds exhibit a maximum change of magnetic entropy of 0.57 (0.48) J kg.K^-1atTFiMin a magnetic field of 5 T. The strong spin-orbit coupling in 5dstates of Ir and cation disorder lead to the Mott insulating phase as found from the analysis of temperature dependent resistivity. These unique behaviors suggest an interesting interplay between localized Pr/Nd-4f, itinerant Co-3dand Ir-5delectrons.

Two-Dimensional Multiferroics with Intrinsic Magnetoelectric Coupling in A-Site Ordered Perovskite Monolayers

The magnetoelectric coupling effect in multiferroics provides a route to realize the control of magnetism by electric field. Here, we demonstrate the coexistence and coupling of ferroelectricity and ferromagnetism in designed A-site ordered perovskite oxide monolayers by combining symmetry analysis and first-principles calculation. These monolayers all exhibit a layered ordering and tilt distortion, and some of them exhibit rotation or Jahn-Teller distortion simultaneously, leading to the emergence of in-plane ferroelectricity. The Mn-based monolayers exhibit robust ferromagnetism, while some monolayers tend to form E-type spin order due to the splitting of the nearest-neighbor exchange interactions. Whether polarization reversal can lead to magnetization reversal depends on the mode of ferroelectric switching, that is, only the ferroelectric switching that reversing the tilt distortion can lead to magnetization reversal. This work demonstrates the feasibility of controlling the direction of magnetization by electric field in the monolayer limit of perovskites.

New Rare Earth-Doped Bilayered Perovskite Oxide Photocatalysts Sr2La0.5R0.5FeMnO7 (R = La, Nd, Sm, Gd, Dy) for the Degradation of Highly Toxic Methylene Blue Dye in Wastewater under Visible Light: Structural, Optical, and Magnetic Properties

This paper presents the rare earth doping effect on the structural, optical, and magnetic properties of bilayered Ruddlesden-Popper oxides Sr₂La_0.5R_0.5FeMnO₇ (R = La, Nd, Sm, Gd, Dy). Moreover, we are reporting for the first time a new rare earth-doped bilayered perovskite oxide series for the highly toxic methylene blue dye degradation in wastewater under visible light. Structural analysis of the PXRD data using the Rietveld refinements confirms the formation of the phases in tetragonal symmetry with the I4/mmm space group. The unit cell lattice parameters (a & c) and the cell volume (V) decrease monotonically from La- to Dy-doped samples owing to the decrease in the lanthanide ionic radii. The X-ray photoelectron spectroscopy analysis indicates the existence of the Mn ions in the mixed valence state. The DRS study shows that the energy band gap value decreases on moving from La to Gd substitution; however, it further increases for the Dy-doped sample. The magnetic measurements reveal that all the phases exhibit dominant anti-ferromagnetic interactions with Neel temperature (T _N) observed at 150, 147, 138, 113, and 117 K for La-, Nd-, Sm-, Gd-, and Dy-substituted phases, respectively. However, the presence of an unsaturated hysteresis loop observed in the isothermal magnetic field (H) vs magnetization (M) plot also indicates the existence of weak ferromagnetic interactions. The investigation of the photocatalytic activity of the synthesized samples was done by carrying out photo-oxidative degradation of methylene blue (MB) dye pollutants. The results show that the photodegradation enhances by doping with heavier rare earth ions with the exception of the Dy-doped sample. The Gd-doped catalyst shows the maximum degradation efficiency of 99.03% in 50 min under visible light irradiation. The scavenging experiments confirmed that the^·OH was the main/dominant oxidizing agent involved in the degradation of the MB dye.

All-in-One Electric Double Layer Supercapacitors Based on CH3NH3PbI3 Perovskite Electrodes

Supercapacitors (SCs) are widely used energy storage devices in various applications that require instantaneous power supply and fast response times; however, the challenge for achieving high performance demands the continuous development and tailoring of electrode materials. Organic-inorganic halide perovskites (OIHPs) have recently received significant attention in electrochemical energy storage and conversion applications due to their unique properties including high charge carrier mobility, high mixed (electronic-ionic) conductivity, and presence of large oxygen vacancies. This study presents the fabrication and use of OIHPs based on methyl-ammonium lead iodide (CH₃NH₃PbI₃) and its Co²⁺- and Bi³⁺-substituted derivatives (CH₃NH₃Pb_1-x Co _x I₃ and CH₃NH₃Pb_1-x Bi _x I₃, respectively, where x = 0.1) as electrodes for SCs. SC devices were constructed symmetrically by sandwiching the synthesized electrode materials in a quasi-solid-state electrolyte between two TiO₂-coated FTO glasses. We discussed the optimization parameters (i.e., A-site doping, B-site doping, and controlling the stoichiometry of the anion and cation) to improve the electrochemical performance of the fabricated SCs. Furthermore, the effects of substitution ions (Co²⁺ and Bi³⁺) on the charge-discharge performance, energy and power density, defects, crystallinity, and microstructure were demonstrated. Electrochemical performances of the electrodes were analyzed by using CV, EIS, and GCPL techniques. The highest power density of 934.6 W/kg was obtained for Bi-substituted perovskite electrodes. Fabricated SC devices show good cyclability with 97.2, 96.3, and 86.6% retention of the initial capacitances after 50 cycles for pure, Co²⁺-substituted, and Bi³⁺-substituted perovskite electrodes, respectively.

Dielectric and Spin-Glass Magnetic Properties of the A-Site Columnar-Ordered Quadruple Perovskite Sm2CuMn(MnTi3)O12

Perovskite-type ABO₃ oxides show a number of cation-ordered structures, which have significant effects on their properties. The rock-salt-type order is dominant for B cations, and the layered order for A cations. In this work, we prepared a new perovskite-type oxide, Sm₂CuMn(MnTi₃)O₁₂, with a rare columnar A-site order using a high-pressure, high-temperature method at about 6 GPa and about 1700 K. Its crystal structure was studied with synchrotron powder X-ray diffraction. The compound crystallizes in space group P4₂/nmc (No. 137) at room temperature with a = 7.53477 Å and c = 7.69788 Å. The magnetic properties of the compound were studied with dc and ac magnetic susceptibility measurements and specific heat. Spin-glass (SG) magnetic properties were found with T_SG = 7 K, while specific heat, in the form of C_p/T, showed a strong, very broad anomaly developing below 20 K and peaking at 4 K. The dielectric constant of Sm₂CuMn(MnTi₃)O₁₂ was nearly frequency and temperature independent between 8 K and 200 K, with a value of about 50. Cu²⁺ doping drastically modified the magnetic and dielectric properties of Sm₂CuMn(MnTi₃)O₁₂ in comparison with the parent compound Sm₂MnMn(MnTi₃)O₁₂, which showed a long-range ferrimagnetic order at 34-40 K. The antisite disorder of Cu²⁺ and Mn²⁺ cations between square-planar and octahedral sites was responsible for the SG magnetic properties of Sm₂CuMn(MnTi₃)O₁₂.

DFT analogue of prospecting the spin-polarised properties of layered perovskites Ba2ErNbO6 and Ba2TmNbO6 influenced by electronic structure

Since the unexpected accelerated discovery of half-metallic perovskites is continuously on the rise both from basic sciences and application-oriented sides. Herein, for the first time in this carried research work, we significantly delivered a detailed analysis on one of experimentally synthesized perovskite structure Ba₂ErNbO₆ and in related to Ba₂TmNbO₆ within the realm of unified density functional theory. Initially, the structural stability of two molecular perovskite structures were critically established interms of their total ground state and cohesive energies by the expendition of Brich Murnaghan equation of state. Also, the tolerance factor (τ) oversees the cubic structural stability without possessing any geometrical strains. More likely, the density functional perturbation theory (DFPT) has been calibrated to perceive the dynamical context of these layered structures. Also, from the understandings of second order elastic and mechanical parameters adresses their suitable ductile characteristics. The quantum mechanical refinement of their intrinsic electronic structures were systematically tuned by the exploitation of Generalised gradient approximation (GGA), on-site Hubbard scheme (GGA + U) selected to the strongly correlated electrons of particular angular momentum and modified Becke-Johnson (mBJ) potential. Moreover, the two-dimensional representation of asymmetric density of states (DOS) pinned around the Fermi-level (E_F) and the interpretation linked to their corresponding spin-polarised band structures signatures the well-known half-metallic nature. Subsequently, the transport properties especially the value of figure of merit (_ZT) equals to unity (1) along the selected chemical potential range at different temperatures. The summed-up properties and the overall tendency triggers the possibility of these materials to register their extending applications in spintronics, thermoelectrics, nanoengineering, and radioisotope generator perspectives.

Alloying Bi-Doped Cs2Ag1-xNaxInCl6 Nanocrystals with K+ Cations Modulates Surface Ligands Density and Photoluminescence Efficiency

We show how, in the synthesis of yellow-emissive Bi-doped Cs2Ag1-xNaxInCl6 double perovskite nanocrystals (NCs), preventing the transient formation of Ag0 particles increases the photoluminescence quantum yield (PLQY) of the NCs from ∼30% to ∼60%. Calculations indicate that the presence of even a single Ag0 species on the surface of a NC introduces deep trap states. The PL efficiency of these NCs is further increased to ∼70% by partial replacement of Na+ with K+ ions, up to a 7% K content, due to a lattice expansion that promotes a more favorable ligands packing on the NC surface, hence better surface passivation. A further increase in K+ lowers the PLQY, due to both the activation of nonradiative quenching channels and a lower oscillator strength of the BiCl6→AgCl6 transition (through which PL emission occurs). The work indicates how a deeper understanding of parameters influencing carrier trapping/relaxation can boost the PLQY of double perovskites NCs.

Rationalization of Double Perovskite Oxides as Energy Materials: A Theoretical Insight from Electronic and Optical Properties

The quest for clean energy conversion has become one of the most important efforts for tackling the greenhouse effect for a sustainable environment. This involves energy-scavenging processes like photovoltaics and catalysis, which have been manifested using the solar spectrum. For high-efficiency and durable conversion processes, the search for the low-cost, stable, and environment-friendly functional materials is elusive. In the field of solar cells and catalysis, double perovskite oxides (DPOs) have emerged as potential candidates in recent years. Through compositional tuning and band gap engineering, a plethora of materials are being developed for pertinent applications in this field of energy. Oxide perovskites possess the advantage of a high carrier lifetime compared to that with halide perovskites, which can be beneficial for energy applications. In this perspective, we have presented theoretical investigations focusing on the different types of double perovskite oxides based on the composition space in a systematic manner. Corresponding electronic and optical properties are discussed along with a future outlook on the novel routes to find efficient members in this family.

Giant magneto optical properties in the double perovskites Ba2B'RuO6(B' = Er, Tm)

This study aimed to investigate new double perovskite oxides in search of new promising functional material with properties of interest for high density storage applications. The crystal structure, magnetic, electronic and magneto-optical properties of the rare-earth-based double perovskites Ba₂B'RuO₆(B' = Er, Tm) were investigated through full-potential linearized augmented plane wave method within the context of density functional theory (DFT) in Wien2k code. We used generalized gradient approximation (GGA) and GGA + U approaches to calculate magneto-optical properties, including spin-orbit coupling due to 4f and 4d-electrons. The obtained DFT-optimized structures was cubic (space group: Fm = 3m), and the calculations (GGA + U) showed that the compounds Ba₂ErRuO₆is semiconductor and the Ba₂TmRuO₆is half-metal. The magneto-optical Kerr effect showed pronounced peaks at angles of 17.7^∘and 5.6^∘for an energy around 0.2 eV for both compounds, which could potentially have important applications in the infrared region or for blue and violet radiation.

Radiation effects, zero thermal expansion, and pressure-induced phase transition in CsMnCo(CN)6

The Prussian blue analogue CsMnCo(CN)₆ is studied using powder X-ray and neutron diffraction under variable temperature, pressure, and X-ray exposure. It retains cubic F4̄3m symmetry in the range 85-500 K with minimal thermal expansion, whereas a phase transition to P4̄n2 occurs at ∼2 GPa, driven by octahedral tilting. A small lattice contraction occurs upon increased X-ray dose. Comparisons with related systems indicate that the Cs^I ions decrease the thermal expansion and suppress the likelihood of phase transformations. The results improve the understanding of the stimuli-responsive behaviour of coordination polymers.

1 : 1 Ca2+ :Cu2+ A-site Order in a Ferrimagnetic Double Double Perovskite

Cation ordering in ABX3 perovskites is important to structural, physical and chemical properties. Here we report discovery of CaCuFeReO6 with the tetragonal AA'BB'O6 double double perovskite structure that was previously only reported for A'=Mn compositions. CaCuFeReO6 occurs in the same phase field as CaCu3 Fe2 Re2 O12 demonstrating that different A-cation ordered peroskites may be obtained in the same chemical system. CaCuFeReO6 has ferrimagnetic order of Fe, Re and Cu spins below TC =567 K, in contrast to Mn analogues where the Mn spins order separately at much lower temperatures. The magnetoresistance of CaCuFeReO6 displays low-field "butterfly" hysteresis with an unusual change from negative to positive values as field increases. Many more AA'BB'O6 double double perovskites may be accessible for A'=Cu and other divalent transition metals at high pressure, so the presently known phases likely represent only the "tip of the iceberg" for this family.

Coexistence and Coupling of Spin-Induced Ferroelectricity and Ferromagnetism in Perovskites

Spin-induced ferroelectricity usually does not occur in perovskites with simple collinear magnetic structures. Here, we demonstrate that in even-layer perovskite systems, some common distortion modes involving octahedral rotation and Jahn-Teller distortion can break the inversion symmetry, allowing the emergence of spin-dependent out-of-plane polarization in a simple magnetic structure. Such spin-induced ferroelectricity is very common in double-perovskite systems and can coexist with ferromagnetism or ferrimagnetism above room temperature. We explain its origin by modifying the spin-dependent p-d hybridization mechanism. Our Letter provides a universal design for two-dimensional multiferroics and enables the control of polarization by means of a magnetic field.

Triple A-Site Cation Ordering in the Ferrimagnetic Y2CuGaMn4O12 Perovskite

A new member of A-site columnar-ordered A₂A′A″B₄O₁₂ quadruple perovskites with the composition of Y₂CuGaMn₄O₁₂ was prepared by a high-pressure, high-temperature method at 6 GPa and about 1500 K. Its crystal structure and cation distributions were studied by powder synchrotron X-ray and neutron diffraction. There is a triple A-site cation ordering with some degrees of anti-site disorder among sites occupied by 3d transition metals: [Y₂]_A[Cu_0.8Mn_0.2]_A′[Ga_0.8Mn_0.2]_A″[Mn_3.6Cu_0.2Ga_0.2]_BO₁₂. It has the space group P4₂/nmc (no. 137) between 1.5 and 873 K with a = 7.33884 Å and c = 7.66251 Å at 297 K. Despite anti-site disorder, it exhibits a long-range ferrimagnetic order at T_C = 115 K with the ordered moment of 2.19 μ_B at each B site and 0.89 μ_B at the A′ or A″ site. Magnetic moments are aligned along the c axis; all moments are ordered ferromagnetically at the B sites, and the moments at the A′ or A″ site are ordered in the opposite direction. Cu²⁺ doping drastically changes magnetic properties as “parent” Y₂MnGaMn₄O₁₂ just shows spin-glass magnetic properties without long-range ordering. Anisotropic thermal expansion was observed in Y₂CuGaMn₄O₁₂: the lattice parameter a almost linearly decreases from 1.5 K to T_C and then monotonically increases up to 873 K (almost linearly from 300 K); the parameter c monotonically increases from 1.5 to 300 K and then decreases up to 600 K.

A new member of the A-site columnar-ordered quadruple perovskite A₂A′A″B₄O₁₂ family, Y₂CuGaMn₄O₁₂, was prepared at high pressure and high temperature, with triple A-site ordering and ferrimagnetic properties.

Multiferroic and Magnetodielectric Effects in Multiferroic Pr2FeAlO6 Double Perovskite

Single-phase multiferroics that allow the coexistence of ferroelectric and magnetic ordering above room temperature are highly desirable, and offer a fundamental platform for novel functionality. In this work, a double perovskite multiferroic Pr₂FeAlO₆ ceramic is prepared using a sol-gel process followed by a quenching treatment. The well-crystallized and purified Pr₂FeAlO₆ in trigonal structure with space group R3c is confirmed. A combination of the ferroelectric (2P_r = 0.84 μC/cm², E_c = 7.78 kV/cm at an applied electric field of 20 kV/cm) and magnetic (2M_r = 433 memu/g, H_c = 3.3 kOe at an applied magnetic field of 1.0 T) hysteresis loops reveals the room-temperature multiferroic properties. Further, the magnetoelectric effect is observed from the measurements of magnetically induced dielectric response and polarization. The present results suggest a new complex oxide candidate for room-temperature multiferroic applications.

The effect of antisite disorder on magnetic and exchange bias properties of Gd-substituted Y2CoMnO6double perovskite

Combining experimental investigations and first-principles density functional theory (DFT) calculations, we report physical and magnetic properties of Gd-substituted Y₂CoMnO₆double perovskite, which are strongly influenced by antisite-disorder-driven spin configurations. On Gd doping, Co and Mn ions are present in mixed-valence (Co³⁺, Co²⁺, Mn³⁺and Mn⁴⁺) states. Multiple magnetic transitions have been observed: (i) paramagnetic to ferromagnetic transition is found to occur atT_C= 95.5 K, (ii) antiferromagnetic transition atT_N= 47 K is driven by3d-4fpolarization and antisite disorder present in the sample, (iii) change in magnetization belowT⩽20 K, primarily originating from Gd ordering, as revealed from our DFT calculations. AC susceptibility measurement confirms the absence of any spin-glass or cluster-glass phases in this material. A significantly large exchange bias effect (HEB= 1.07 kOe) is found to occur below 47 K due to interfaces of FM and AFM clusters created by antisite-disorder.

High-Throughput Selection and Experimental Realization of Two New Ce-Based Nitride Perovskites: CeMoN3 and CeWN3

Nitride perovskites have only been experimentally realized in very few cases despite the widespread existence and commercial importance of perovskite materials. From oxide perovskites used in ultrasonics to halide perovskites that have revolutionized the photovoltaics industry, the discovery of new perovskite materials has historically impacted a wide number of fields. Here, we add two new perovskites, CeWN₃ and CeMoN₃, to the list of experimentally realized perovskite nitrides using high-throughput computational screening and subsequent high-throughput thin film growth techniques. Candidate compositions are first down-selected using a tolerance factor and then thermochemical stability. A novel competing fluorite-family phase is identified for both material systems, which we hypothesize is a transient intermediate phase that crystallizes during the evolution from an amorphous material to a stable perovskite. Different processing routes to overcome the competing fluorite phase and obtain phase-pure nitride perovskites are demonstrated for the CeMoN_3-x and CeWN_3-x material systems, which provide a starting point for the development of future nitride perovskites. Additionally, we find that these new perovskite phases have interesting low-temperature magnetic behavior: CeMoN_3-x orders antiferromagnetically below T _N ≈ 8 K with indications of strong magnetic frustration, while CeWN_3-x exhibits no long-range order down to T = 2 K but has strong antiferromagnetic correlations. This work demonstrates the importance and effectiveness of using high-throughput techniques, both computational and experimental: they are integral to optimize the process of realizing two entirely novel nitride perovskites.

Hierarchical Symbolic Regression for Identifying Key Physical Parameters Correlated with Bulk Properties of Perovskites

Symbolic regression identifies nonlinear, analytical expressions relating materials properties and key physical parameters. However, the pool of expressions grows rapidly with complexity, compromising its efficiency. We tackle this challenge hierarchically: identified expressions are used as inputs for further obtaining more complex expressions. Crucially, this framework can transfer knowledge among properties, as demonstrated using the sure-independence-screening-and-sparsifying-operator approach to identify expressions for lattice constant and cohesive energy, which are then used to model the bulk modulus of ABO_{3} perovskites.

Double glassy states and large spontaneous and conventional exchange bias in La1.5Ca0.5CoFeO6ferrimagnetic double perovskite

The structural and magnetic properties of hole doped double perovskite La_1.5Ca_0.5CoFeO₆have been investigated by measuring x-ray photoemission spectroscopy, neutron powder diffraction and magnetization. A ferrimagnetic transition is observed atT_C∼ 167 K. The presence of anti-site disorder (ASD) in La_1.5Ca_0.5CoFeO₆has also been demonstrated. Double re-entrant cluster glass transitions (T₁∼ 11 K andT_S∼ 35 K) were observed which has been attributed to the ASD effect. The presence of both large spontaneous exchange biasH_SEB∼ 2.106 kOe and giant conventional exchange biasH_CEB∼ 1.56 T at 5 K has also been observed which can be attributed to the coexistence of long range magnetic ordering and glassy state. The experimental observations were explained with the results obtained by the density functional theory calculation. The presence of double glassy states, large exchange-bias effect and different magnetic phases make this system a potential candidate for spintronic applications.

Chemical pressure in functional materials

Chemical pressure, a strange but familiar concept, is a lattice internal force caused by lattice strain with chemical modifications and arouses great interest due to its diversity and efficiency to synthesize new compounds and tune functional materials. Different from physical pressure loaded by an external force that is positive, chemical pressure can be either positive or negative (contract a lattice or expand it), often through flexible and mild chemical synthesis strategies, which are particularly important as a degree of freedom to manipulate material behaviors. In this tutorial review, we summarize the features of chemical pressure as a methodology and demonstrate its role in synthesizing and discovering some typical magnetically, electrically, and thermally responsive functional materials. The measure of chemical pressure using experimental lattice strain and elastic modulus was proposed, which can be used for quantitative descriptions of the correlation between lattice distortion and properties. From a lattice strain point of view, we classify chemical pressure into different categories: (i) chemical substitution, (ii) chemical intercalation/de-intercalation, (iii) size effect, and (iv) interface constraint, etc. Chemical pressure affects chemical bonding and rationalizes the crystal structure by modifying the electronic structure of solids, regulating the lattice symmetry, local structure, phonon structure effects etc., emerging as a general and effective method for synthesizing new compounds and tuning functional materials.

Double Perovskite Ba2LaTaO6 for Ultrafast Fiber Lasers in Anomalous and Normal Net Dispersion Regime

Double perovskites (DPs) have been attracting attention in an assortment of optoelectronic applications, for they hold advantages such as high quantum efficiency, long carrier migration distance and strong linear and nonlinear absorptions. As specific kinds of perovskites (PVKs), DPs are gifted with orthorhombic crystal structures which provide rich conversion combinations and broaden the space for research and application. However, few works have been reported about DPs in ultrafast photonics applications. In this article, a DP with chemical formula of Ba₂LaTaO₆ (BLT) was successfully synthesized by high-temperature solid phase method. The microstructures and morphologies were observed, and the linear and nonlinear absorption were characterized. By first using BLT as a novel saturable absorber in both normal and anomalous dispersion region fiber lasers, dual-wavelength soliton and dissipative soliton were successfully operated at C-band. This study affirms BLT’s nonlinear optical properties, lays the foundation for optical research on BLT, and meanwhile provides a meaningful reference for future development of pulsed lasers based on DPs.

Synthesis Attempt and Structural Studies of Novel A2CeWO6 Double Perovskites (A2+ = Ba, Ca) in and outside of Ambient Conditions

This comprehensive work showcases two novel, rock-salt-type minerals in the form of amphoteric cerium-tungstate double perovskite and ilmenite powders created via a high-temperature solid-state reaction in inert gases. The presented studies have fundamental meaning and will mainly focus on a detailed synthesis description of undoped structures, researching their possible polymorphism in various conditions and hinting at some nontrivial physicochemical properties like charge transfer for upcoming optical studies after eventual doping with selectively chosen rare-earth ions. The formerly mentioned, targeted A₂BB'X₆ group of compounds contains mainly divalent alkali cations in the form of ^XIIA = Ba²⁺, Ca²⁺ sharing, here, oxygen-arranged clusters (^IIX = O^2-) with purposely selected central ions from f-block ^VIB = Ce^4/3+ and d-block ^VIB' = W^4/5/6+ since together they often possess some exotic properties that could be tuned and implemented into futuristic equipment like sensors or energy converters. Techniques like powder XRD, XPS, XAS, EPR, Raman, and FTIR spectroscopies alongside DSC and TG were involved with an intent to thoroughly describe any possible changes within these materials. Mainly, to have a full prospect of any desirable or undesirable phenomena before diving into more complicated subjects like: energy or charge transfer in low temperatures; to reveal whether or not the huge angular tilting generates large enough dislocations within the material's unit cell to change its initial properties; or if temperature and pressure stimuli are responsible for any phase transitions and eventual, irreversible decomposition.

Recent Advances in Perovskite Catalysts for Efficient Overall Water Splitting

Hydrogen is considered a promising clean energy vector with the features of high energy capacity and zero-carbon emission. Water splitting is an environment-friendly and effective route for producing high-purity hydrogen, which contains two important half-cell reactions, namely, the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). At the heart of water splitting is high-performance electrocatalysts that efficiently improve the rate and selectivity of key chemical reactions. Recently, perovskite oxides have emerged as promising candidates for efficient water splitting electrocatalysts owing to their low cost, high electrochemical stability, and compositional and structural flexibility allowing for the achievement of high intrinsic electrocatalytic activity. In this review, we summarize the present research progress in the design, development, and application of perovskite oxides for electrocatalytic water splitting. The emphasis is on the innovative synthesis strategies and a deeper understanding of structure–activity relationships through a combination of systematic characterization and theoretical research. Finally, the main challenges and prospects for the further development of more efficient electrocatalysts based on perovskite oxides are proposed. It is expected to give guidance for the development of novel non-noble metal catalysts in electrochemical water splitting.

Frustration, strain and phase co-existence in the mixed valent hexagonal iridate Ba3NaIr2O9

Using detailed synchrotron diffraction, magnetization, thermodynamic and transport measurements, we investigate the relationship between the mixed valence of Ir, lattice strain and the resultant structural and magnetic ground states in the geometrically frustrated triple perovskite iridate Ba₃NaIr₂O₉. We observe a complex interplay between lattice strain and structural phase co-existence, which is typically not observed in this family of compounds. The low temperature magnetic ground state is characterized by the absence of long-range magnetic order, and points towards the condensation of a cluster glass state from an extended regime of short range magnetic correlations.

Free-Spin Dominated Magnetocaloric Effect in Dense Gd3+ Double Perovskites

Frustrated lanthanide oxides with dense magnetic lattices are of fundamental interest for their potential in cryogenic refrigeration due to a large ground state entropy and suppressed ordering temperatures but can often be limited by short-range correlations. Here, we present examples of frustrated fcc oxides, Ba₂GdSbO₆ and Sr₂GdSbO₆, and the new site-disordered analogue Ca₂GdSbO₆ ([CaGd] _A [CaSb] _B O₆), in which the magnetocaloric effect is influenced by minimal superexchange (J ₁ ∼ 10 mK). We report on the crystal structures using powder X-ray diffraction and the bulk magnetic properties through low-field susceptibility and isothermal magnetization measurements. The Gd compounds exhibit a magnetic entropy change of up to -15.8 J/K/mol_Gd in a field of 7 T at 2 K, a 20% excess compared to the value of -13.0 J/K/mol_Gd for a standard in magnetic refrigeration, Gd₃Ga₅O₁₂. Heat capacity measurements indicate a lack of magnetic ordering down to 0.4 K for Ba₂GdSbO₆ and Sr₂GdSbO₆, suggesting cooling down through the liquid 4-He regime. A mean-field model is used to elucidate the role of primarily free-spin behavior in the magnetocaloric performance of these compounds in comparison to other top-performing Gd-based oxides. The chemical flexibility of the double perovskites raises the possibility of further enhancement of the magnetocaloric effect in the Gd³⁺ fcc lattices.

Observation of Anisotropic Thermal Expansion and the Jahn-Teller Effect in Double Perovskites Sr2-xLaxCoNbO6 Using Neutron Diffraction

We use temperature dependent neutron powder diffraction (NPD) to investigate the structural changes and magnetic interactions in double perovskite Sr_2-xLa_xCoNbO₆ (x = 0.4 and 0.6). A structural phase transition from tetragonal (I4/m) to monoclinic (P2₁/n) is observed between x = 0.4 and 0.6 samples. Interestingly, the temperature evolution of the unit cell parameters follows the Grüneisen approximation, and the analysis suggests an isotropic thermal expansion in the case of the x = 0.4 sample, whereas the x = 0.6 sample shows the anisotropy where the thermal expansion along the c-axis significantly deviates from the Grüneisen function. We observe the z-out Jahn-Teller distortion in the CoO₆ and consequently z-in distortion in the adjacent NbO₆ octahedra. With an increase in the La substitution, a decrease in the degree of octahedral distortion is evident from the significant reduction in the local distortion parameter Δ around the B-site atoms.

Selective Catalytic Reduction of NOx over Perovskite-Based Catalysts Using CxHy(Oz), H2 and CO as Reducing Agents-A Review of the Latest Developments

Selective catalytic reduction (SCR) is probably the most widespread process for limiting NO_x emissions under lean conditions (O₂ excess) and, in addition to the currently used NH₃ or urea as a reducing agent, many other alternative reductants could be more promising, such as C_xH_y/C_xH_yO_z, H₂ and CO. Different catalysts have been used thus far for NO_x abatement from mobile (automotive) and stationary (fossil fuel combustion plants) sources, however, perovskites demand considerable attention, partly due to their versatility to combine and incorporate various chemical elements in their lattice that favor deNO_x catalysis. In this work, the C_xH_y/C_xH_yO_z⁻, H₂⁻, and CO-SCR of NO_x on perovskite-based catalysts is reviewed, with particular emphasis on the role of the reducing agent nature and perovskite composition. An effort has also been made to further discuss the correlation between the physicochemical properties of the perovskite-based catalysts and their deNO_x activity. Proposed kinetic models are presented as well, that delve deeper into deNO_x mechanisms over perovskite-based catalysts and potentially pave the way for further improving their deNO_x efficiency.

Site-Selective d10/d0 Substitution in an S = 1/2 Spin Ladder Ba2CuTe1-xWxO6 (0 ≤ x ≤ 0.3)

Isovalent nonmagnetic d10 and d0 B″ cations have proven to be a powerful tool for tuning the magnetic interactions between magnetic B' cations in A2B'B″O6 double perovskites. Tuning is facilitated by the changes in orbital hybridization that favor different superexchange pathways. This can produce alternative magnetic structures when B″ is d10 or d0. Furthermore, the competition generated by introducing mixtures of d10 and d0 cations can drive the material into the realms of exotic quantum magnetism. Here, Te6+ d10 was substituted by W6+ d0 in the hexagonal perovskite Ba2CuTeO6, which possesses a spin ladder geometry of Cu2+ cations, creating a Ba2CuTe1-xWxO6 solid solution (x = 0-0.3). We find W6+ is almost exclusively substituted for Te6+ on the corner-sharing site within the spin ladder, in preference to the face-sharing site between ladders. The site-selective doping directly tunes the intraladder, Jrung and Jleg, interactions. Modeling the magnetic susceptibility data shows the d0 orbitals modify the relative intraladder interaction strength (Jrung/Jleg) so the system changes from a spin ladder to isolated spin chains as W6+ increases. This further demonstrates the utility of d10 and d0 dopants as a tool for tuning magnetic interactions in a wide range of perovskites and perovskite-derived structures.

Photocatalysis and perovskite oxide-based materials: a remedy for a clean and sustainable future

The massive use of non-renewable energy resources by humankind to fulfill their energy demands is causing severe environmental issues. Photocatalysis is considered one of the potential solutions for a clean and sustainable future because of its cleanliness, inexhaustibility, efficiency, and cost-effectiveness. Significant efforts have been made to design highly proficient photocatalyst materials for various applications such as water pollutant degradation, water splitting, CO2 reduction, and nitrogen fixation. Perovskite photocatalyst materials are gained special attention due to their exceptional properties because of their flexibility in chemical composition, structure, bandgap, oxidation states, and valence states. The current review is focused on perovskite materials and their applications in photocatalysis. Special attention has been given to the structural, stoichiometric, and compositional flexibility of perovskite photocatalyst materials. The photocatalytic activity of perovskite materials in different photocatalysis applications is also discussed. Various mechanisms involved in photocatalysis application from wastewater treatment to hydrogen production are also provided. The key objective of this review is to encapsulate the role of perovskite materials in photocatalysis along with their fundamental properties to provide valuable insight for addressing future environmental challenges.