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Published on: February 15, 2016
Crystal structure and stability of β-Na(2)ThF(6) at non-ambient conditions
Andrzej Grzechnik1, Michael Fechtelkord, Wolfgang Morgenroth
1Departamento de Física de la Materia Condensada, Universidad del País Vasco, Bilbao, Spain.
Abstract:
The crystal structure and stability of β-Na(2)ThF(6) at non-ambient conditions have been studied with calorimetric analysis, second harmonic generation measurements, and (19)F and (23)Na magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, as well as synchrotron x-ray single-crystal and powder diffraction. The twinned structure (P321, Z = 1) is built of chains of capped trigonal prisms around the Th atoms formed along the c-axis through sharing of the basal faces. More distorted capped trigonal prisms around the Na atoms share their basal and equatorial faces with each other. The twin operation is a two-fold rotation around the c-axis. β-Na(2)ThF(6) is stable in the temperature and pressure ranges of 100-954 K and 0.0001-6.4 GPa, respectively. The Na-F distances are more compressible than the Th-F distances. A hypothetical ferroelastoelectric and ferrobielastic [Formula: see text] phase transition is discussed.
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