Crystal structure of the Sr6Nb4ZrO18 slab perovskite-like compound

The Sr6Nb4ZrO18 niobatozirconate has been synthesized from the Sr5Nb4O15 four-layer perovskite and the SrZrO3 perovskite at T = 1670 K by ceramic technique. Crystal structure of the Sr6Nb4ZrO18 compound has been studied by the X-ray powder diffraction method. It was shown that crystal structure of the Sr6Nb4ZrO18 (a = 0.5687(1) nm, c = 4.146(1) nm, R-3m space group) belongs to the Ba6Nb4TiO18-type with five-layer perovskite-like structure. The crystal structure features of the Sr6Nb4BIVO18 compounds (BIV = Ti, Sn, Zr) has been analyzed. The correlation between composition and crystal structure features for all Sr6Nb4BIVO18 (BIV = Ti, Sn, Zr) compounds, which leads to destruction slab perovskite-like structure has been revealed

Ab-initio\textit{Ab-initio} study of ABiO3\textit{A}BiO_3 (AA=Ba, Sr, Ca) under high pressure

Using $\textit{ab-initio}$ crystal structure prediction we study the high-pressure phase diagram of $\textit{A}BiO_3$ bismuthates ($A$=Ba, Sr, Ca) in a pressure range up to 100$~$GPa. All compounds show a transition from the low-pressure perovskite structure to highly distorted, low-symmetry phases at high pressures (PD transition), and remain charge disproportionated and insulating up to the highest pressure studied. The PD transition at high pressures in bismuthates can be understood as a combined effect of steric arguments and of the strong tendency of bismuth to charge-disproportionation. In fact, distorted structures permit to achieve a very efficient atomic packing, and at the same time, to have Bi-O bonds of different lengths. The shift of the PD transition to higher pressures with increasing cation size within the $\textit{A}BiO_3$ series can be explained in terms of chemical pressure

Особливостi розподiлу катiонiв у п’ятишаровiй перовскiтоподiбнiй структурi сполук та фаз типу AnBnO3n+2

The crystal layer perovskite-like structures (LPS) of five-slab phases Ca5-xSrxTiNb4O17 (x = 1, 2, 3, 4) have been determined by X-ray powder diffraction. The peculiarities of LPS of synthesized phases and the known five-slab compounds of the A5BIBII 4 O17 type have been analyzed and the regularities of the distribution of B-type cations in the five-slab perovskite-like structure of compounds and phases of the A5BIBII 4 O17 type have been determined