title: Crystal structure and stability of β-Na(2)ThF(6) at non-ambient conditions.
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.
authors.affiliation: Departamento de Física de la Materia Condensada, Universidad del País Vasco, Bilbao, Spain.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Grzechnik
authors.forename: Michael
authors.initials: M
authors.lastname: Fechtelkord
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Morgenroth
authors.forename: Jose
authors.initials: J
authors.lastname: María Posse
authors.forename: Karen
authors.initials: K
authors.lastname: Friese