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Ferroelastic phase transitions in (NH4)2TaF7 |
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| Authors: | E I Pogorel’tsev S V Mel’nikova A V Kartashev M S Molokeev M V Gorev I N Flerov N M Laptash |
| Institution: | 1557. Kirensky Institute of Physics, Siberian Branch of the Russian Academy of Sciences, Akademgorodok 50-38, Krasnoyarsk, 660036, Russia 2557. Institute of Engineering Physics and Radio Electronics, Siberian Federal University, ul. Kirenskogo 28, Krasnoyarsk, 660074, Russia 3557. Institute of Chemistry, Far-Eastern Branch of the Russian Academy of Sciences, pr. Stoletiya Vladivostoka 159, Vladivostok, 690022, Russia |
| Abstract: | The heat capacity, unit cell parameters, permittivity, optical properties, and thermal expansion of the (NH4)2TaF7 compound with a seven-coordinated anion polyhedron have been measured. It has been found that the compound undergoes two successive phase transitions with the symmetry change: tetragonal → (T 1 = 174 K) orthorhombic → (T 2 = 156 K) tetragonal. The ferroelastic nature of structural transformations has been established, and their entropy and susceptibility to hydrostatic pressure have been determined. |
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