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.

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 (□).

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.

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.

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.