Ba(33)Zn(22)Al(8)O(67) with a Framework of ([O(Zn/Al)(4)]/Ba)(Zn/AlO(4))(4) Motifs

[Image: see text] 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 F23) 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.