Synthesis and characterization of novel 6-H perovskites Ba 2Co 2−xSb xO 6−y, 0.6 ≤ x ≤ 0.8 and x = 1.33 (Ba 3CoSb 2O 9)

Abstract

6-H perovskites with compositions Ba 2Co 2− x Sb x O 6− y , 0.6≤ x≤0.8 and x=1.33 (Ba 3CoSb 2O 9) have been prepared in air at 1150 °C. Refinements of the crystal structures of Ba 2Co 1.4Sb 0.6O 6− y and Ba 3CoSb 2O 9 were performed in space group P6 3/ mmc, using neutron and X-ray powder diffraction data, respectively: Ba 2Co 1.4Sb 0.6O 6− y a=5.7315(1) Å, c=14.1118(4) Å, R F 2=0.0669, R p=0.0464, χ 2=1.39; Ba 3CoSb 2O 9 a=5.85321(7) Å, c=14.4454(2) Å, R F 2=0.0458, R p=0.0258, χ 2=1.24. In Ba 3CoSb 2O 9 the antimony atoms are located in pairs of face-sharing octahedra separated by cobalt atoms in octahedral layers, while in Ba 2Co 1.4Sb 0.6O 6− y a random distribution of B cations was found. In the latter structure, oxygen vacancies are preferably located in BaO 3 planes separating the face-sharing octahedra. Electron diffraction and high-resolution electron microscopy studies showed that the structures are well ordered. Results of the magnetic susceptibility measurements of Ba 3CoSb 2O 9 and Ba 2Co 1.4Sb 0.6O 6− y are reported.