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

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journal contribution
posted on 27.10.2021, 14:48 authored by Rayko Simura, Kyosuke Sawamura, Hisanori Yamane, Takuji Ikeda
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.