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

High Resolution Image Download MS PowerPoint Slide Single crystals of a new oxide, Ba 33 Zn 22 Al 8 O 67 (melting point = 1452 K), were grown in a melt-solidified sample prepared by heating a compact of a BaCO 3, ZnO, and Al 2 O 3 mixed powder in a dry airflow. Ba 33 Zn 22 Al 8 O 67 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 Ba 33 Zn 22 Al 8 O 67 crystallizes in a cubic cell ( a = 16.3328 (3) Å, space group F 23) having a three-dimensional Zn/AlO 4 framework in which {([OZn 4 ]/Ba)(Zn/AlO 4 ) 4 } motifs are connected to each other by bridging Zn/AlO 4 tetrahedra. A Ba atom or a [OZn 4 ] 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/AlO 4 ) 4 }, are isolated from the Zn/AlO 4 framework. These motifs, {([OZn 4 ]/Ba)(Zn/AlO 4 ) 4 } and {([O(Zn/Al) 4 ])(Zn/AlO 4 ) 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 Ba 33 Zn 22 Al 8 O 67 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.

Abstract licence: CC BY-NC-ND

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