Synthesis and structural study of hexagonal perovskites in the Ba5Ta4O15-MZrO3 (M = Ba, Sr) system

摘要

New ration-deficient perovskite-like oxides Ba5MTa4ZrO18 and Ba5MTa4Zr2O21 (M = Ba, Sr) were synthesized and studied by X-ray diffraction, electron diffraction, and high-resolution electron microscopy (HREM). The Ba5SrTa4ZrO18 (space group R (3) over bar m, (hcccch), a = 5.80162(8) Angstrom, c = 42.5403(8) Angstrom, R-1 = 0.039, R-p = 0.082) and Ba5Sr2Ta4ZrO21 (space group R (3) over bar m, (hccccch)(3), 5.7998(1) Angstrom, c 49.595(1) Angstrom, R-1 =0.033,R-p = 0.080)crystal structures were refined from X-rag powder diffraction data, The results of structure refinements were confirmed by HREM observations. The formation of the Ba5Sr4Ta4Zr3O24 compound was revealed and the structure of this compound was deduced from HREM (space group P (3) over bar m1, hcccccch, a approximate to 5.8 Angstrom, c approximate to 18.9 Angstrom). All these compounds belong to the A(n)B(n-1)O(3n) homologous series of cation-deficient hexagonal perovskite-like oxides with n = 6, 7, and 8 and may be formally described as intergrowth structures with alternating Ba5Ta4O15-type and Ba(Sr)ZrO3-type structural blocks along the c axis. (C)1998 Academic Press. [References: 13]