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.

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

Single crystals of Ba2YAlO5 and of the α and ß 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) Šand ß = 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) Šand ß = 107.7940 (10)°, and the space group Pm, and ß-Ba6Y2Al4O15 was found to be monoclinic, with a = 7.8310 (2), b = 5.8990 (2), c = 18.3344 (6) Šand ß = 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.

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.

Sr9La2(WO6)4 containing [WO6] octa-hedra.

A polycrystalline sample of Sr9La2(WO6)4, nona-strontium dilanthanum tetra-kis-[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 tetra-gonal space group I41/a and is isotypic with Sr11(ReO6)4. Two W sites with site symmetries of are located at the center of isolated [WO6] octa-hedra, and four mixed (Sr/La) sites are surrounded by eight to twelve O atoms of the [WO6] octa-hedra. 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 (□).

Na3MgB37Si9: an icosa-hedral B12 cluster framework containing {Si8} units.

Single crystals of a novel sodium-magnesium boride silicide, Na3MgB37Si9 [a = 10.1630 (3) Å, c = 16.5742 (6) Å, space group R m (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 inter-stitial site of the Dy2.1B37Si9-type structure with an occupancy of 0.5. The (001) layers of B12 icosa-hedra 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.

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.

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.

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 La3Cr9.24N11 (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.

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

The title silver carbonate iodide, Ag10(CO3)3I4, deca-silver(I) tris-(carbonate) tetra-iodide, 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 inter-calated between the layers of hexa-gonally 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 (K0.2Sr0.8)(Na0.01Ca0.25Bi0.74)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 ß = 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 Ba0.9Ce0.1LuAl0.2Si3.8N6.9O0.1 (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 hexa-gonal (lattice constants: a = 6.0378 (5) Å, c = 9.8133 (9) Å; space group: P63 mc) and isostructural with BaYbSi4N7. (Ba,Ce) and Lu atoms occupy twelvefold and sixfold coordination sites, respectively.

Crystal structure of lutetium aluminate (LUAM), Lu4Al2O9.

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 di-tetra-hedra and Lu-centered six- and sevenfold oxygen polyhedra. The unit-cell volume, 787.3 (3) Å3, is the smallest among the volumes of the rare-earth (RE) aluminates, RE 4Al2O9. 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 ((Na0.75Bi0.25)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 ß = 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, Ca0.99Eu0.01AlSi4N7, 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.

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

Single crystals of the title compound barium zinc copper, BaCu2.6Zn2.4, 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 BaCu2.6Zn2.4 crystallizes in an ortho-rhom-bic 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 BaCu2.6Zn2.4 [452.507 (19) Å3] is smaller than that of α-SrZn5 [466.08 Å3]. 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 inter-atomic 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.

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.

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 O2- 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.