A non-typical sequence of phase transitions in (NH4)(3)GeF7: optical and structural characterization

Описание

Тип публикации: статья из журнала

Год издания: 2016

Идентификатор DOI: 10.1039/c5dt04907e

Аннотация: Single crystals of germanium double salt (NH4)(3)GeF7 = (NH4) 2GeF6 center dot NH4F = (NH4)(3)[GeF6]F were grown and studied by the methods of polarization optics and X-ray diffraction. The birefringence Delta n = (n(o) - n(e)), the rotation angle of the optical indicatrix phi(T) and unit cell parameters were measured in the temperПоказать полностьюature range 100-400 K. Three structural phase transitions were found at the temperatures: T-1 down arrow = 279.2 K (T-1 up arrow = 279.4 K), T-2 up arrow = 270 K (T-2 down arrow = 268.9 K), T-3 down arrow = 218 K (T-3 up arrow = 227 K). An unusual sequence of symmetry transformations with temperature change was established: P4/mbm (Z = 2) (G1) Pbam (Z = 4) (G2) P2(1)/c (Z = 4) (G3) Pa (3) over bar (Z = 8) (G(4)). The crystal structures of different phases were determined. The experimental data were additionally interpreted by a group-theoretical analysis of the complete condensate of order parameters taking into account the critical and noncritical atomic displacements. Strengthening of the N-H center dot center dot center dot F hydrogen bonds can be a driving force of the observed phase transitions.

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Издание

Журнал: DALTON TRANSACTIONS

Выпуск журнала: Vol. 45, Is. 12

Номера страниц: 5321-5327

ISSN журнала: 14779226

Место издания: CAMBRIDGE

Издатель: ROYAL SOC CHEMISTRY

Авторы

  • Mel'Nikova S.V. (Laboratory of Crystal Physics,Kirensky Institute of Physics,SB RAS)
  • Molokeev M.S. (Department of Physics,Far Eastern State Transport University)
  • Laptash N.M. (Institute of Chemistry,Far Eastern Branch of RAS)
  • Misyul S.V. (Siberian Federal University)

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