Synthesis and crystal structure of the A6B5O18 perovskite-like compounds

Abstract New members of the A n B n −1 O 3 n perovskite-like family (Ba 5 KNb 5 O 18 and Sr 6 Nb 4 SnO 18 compounds) with n  = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba 6 Nb 4 TiO 18 -type with a  = 0.57840(7) nm, c  = 4.2532(5) nm and a  = 0.5661(1) nm, c  = 4.186(1) nm for Ba 5 KNb 5 O 18 and Sr 6 Nb 4 SnO 18 , respectively. It was shown that Ba and K ( A -atoms) are completely disordered in the crystal structure of Ba 5 KNb 5 O 18 compound. But Nb and Sn atoms ( B -atoms) in the crystal structure of the Sr 6 Nb 4 SnO 18 compound are quite ordered with the preferred Sn +4 and Nb 5+ cations localization in the center of perovskite-like block and on the boundaries of these blocks, respectively. Temperature and frequency dependencies of the real components of electric conductivity σ I and dielectric permeability ɛ I ; specific electric conductivity at the direct current σ dc have been obtained by the impedance spectroscopy method for Sr 6 Nb 4 SnO 18 .