POLYMORPHIC HIGH PRESSURE MODIFICATION OF FIVE-SLAB ANBNO3N+2 COMPOUNDS
DOI:
https://doi.org/10.15407/dopovidi2024.06.003Keywords:
AnBnO3n+2 compounds, slab perovskite-like structure, high-pressure modificationsAbstract
Phase relations in two-phase (phase with pyrochlore-type structure + trace amounts of phase with lamellar perovskite- like structure) polycrystalline samples of general composition АІІSm4Ti5O17 (АІІ = Ca, Sr) та Sm5Ti4FeO17 and Sm5Ti4GaO17 after their processing at high pressure and temperature (8.5 · 109 Pa, 1770 K £ T £ 2170 K) and subsequent quenching to room conditions have been investigated. On the example of Sm5Ti4GaO17, the principal possibility of obtaining high-pressure polymorphic modifications with a five-slit structure of AnВnО3n+2 type has been shown for the first time. The crystallographic parameters of the monoclinic high-pressure modification of Sm5Ti4GaO17 are: a = 0.7662(2) nm, b = 3.1428(4) nm, c = 0.5442(2) nm, Ðg = 97.03(8)°, Z = 4. The reverse transition of metastable under normal conditions high-pressure Sm5Ti4GaO17 modification into a modification with a pyrochlore-type structure occurs at atmospheric pressure at T ³ 1070 K, and its nature is close to transitions of the second kind.
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