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
Журнал: Journal of Fluorine Chemistry
Выпуск журнала: Vol. 204
Номера страниц: 45-49
ISSN журнала: 00221139
Издатель: Elsevier B.V.