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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 |
| Affiliation: | 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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