Synthesis and crystal structure of the A6B5O18 perovskite-like compounds

• Ba5KNb5O18 and Sr6Nb4SnO18 compounds have been synthesized.
• Their crystal structures were found to belong to the Ba6Nb4TiO18-type.
• Content/structure feature correlations for AII6Nb4BIVO18 compounds have analyzed.
• Electrophysical properties obtained by impedance spectroscopy for Sr6Nb4SnO18.

New members of the AnBn−1O3n perovskite-like family (Ba5KNb5O18 and Sr6Nb4SnO18 compounds) with n = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba6Nb4TiO18-type with a = 0.57840(7) nm, c = 4.2532(5) nm and a = 0.5661(1) nm, c = 4.186(1) nm for Ba5KNb5O18 and Sr6Nb4SnO18, respectively. It was shown that Ba and K (A-atoms) are completely disordered in the crystal structure of Ba5KNb5O18 compound. But Nb and Sn atoms (B-atoms) in the crystal structure of the Sr6Nb4SnO18 compound are quite ordered with the preferred Sn+4 and Nb5+ 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 σI and dielectric permeability ɛI; specific electric conductivity at the direct current σdc have been obtained by the impedance spectroscopy method for Sr6Nb4SnO18.

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