(NH4)3HfF7: Crystallooptical and calorimetric studies of a number of successive phase transitions

Описание

Тип публикации: статья из журнала

Год издания: 2017

Идентификатор DOI: 10.1016/j.jfluchem.2017.10.004

Аннотация: Single crystals of (NH4)3HfF7 were grown. Polarising optical observations as well as measurement of the heat capacity and birefringence Δn(Т) were performed in the temperature range of 200–310 K. Reversible phase transitions at temperatures T0 = 290 K, Т1 = 280.5 K, Т2 ≈ 273 K, Т3 = 266 K, Т4 = 259 K, Т5 = 231 K, Т6 = 229 K were foПоказать полностьюund. Observations in polarised light make it possible to suggest a sequence of changes in the symmetry groups for these transitions: Fm3¯m ⟵Т0→ cub. ⟵Т1→ mmm (1) ⟵Т2→ mmm (2) ⟵Т3→ mmm (3) ⟵Т5→ 2/c. The T-p phase diagram was studied and the temperature boundaries of the stability of the distorted crystalline phases were determined. A significant change of the entropy at successive phase transitions ΣΔS = 10.6 J/mol K indicates a disordering of the initial cubic phase. © 2017

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Издание

Журнал: Journal of Fluorine Chemistry

Выпуск журнала: Vol. 204

Номера страниц: 45-49

ISSN журнала: 00221139

Издатель: Elsevier B.V.

Авторы

  • Pogoreltsev E. (Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russian Federation, Institute of Engineering Physics and Radioelectronics, Siberian Federal University, Krasnoyarsk, Russian Federation)
  • Bogdanov E. (Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russian Federation, Institute of Engineering Systems and Energy, Krasnoyarsk State Agrarian University, Krasnoyarsk, Russian Federation)
  • Melnikova S. (Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russian Federation)
  • Flerov I. (Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russian Federation, Institute of Engineering Physics and Radioelectronics, Siberian Federal University, Krasnoyarsk, Russian Federation)
  • Laptash N. (Institute of Chemistry, Far Eastern Department of RAS, Vladivostok, Russian Federation)

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