ic5018246_si_003.cif (20 kB)
Morphotropy and Temperature-Driven Polymorphism in A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) Series
dataset
posted on 2014-10-20, 00:00 authored by Na Yu, Vladislav V. Klepov, Giuseppe Modolo, Dirk Bosbach, Evgeny
V. Suleimanov, Thorsten M. Gesing, Lars Robben, Evgeny V. AlekseevA new
alkaline thorium arsenate family was obtained and systematically
investigated. The structures of A2Th(AsO4)2 (A = Li, Na, K, Rb, Cs) were determined from single crystal
X-ray diffraction data. Li2Th(AsO4)2 and either isostructural K2Th(AsO4)2 and Rb2Th(AsO4)2 crystallize in
the monoclinic crystal system. Na2Th(AsO4)2 and Cs2Th(AsO4)2 crystallize
in the orthorhombic and tetragonal crystal systems, respectively.
Li2Th(AsO4)2 consists of [Th(AsO4)2]2– layers with Li atoms in
the interlayer space. The rest of the compounds are based on 3D frameworks.
Differences in local environments of ThO8 coordination
polyhedra are described in relation to the symmetry. Despite different
local environments of ThO8 coordination polyhedra and different
structural symmetry, underlying nets of A2Th(AsO4)2 (A = Na, K, Rb, Cs) were shown to be the same. Single-crystal
and powder Raman spectra were measured, and bands are assigned. DSC
measurements showed phase transitions in K2Th(AsO4)2 and Rb2Th(AsO4)2,
which were studied using high-temperature powder X-ray diffraction
(HT-PXRD). The data of HT-PXRD demonstrates two high-temperature polymorphic
modification of K2Th(AsO4)2 and only
one for the isotypic Rb2Th(AsO4)2. The phase transitions in both K and Rb phases are reversible.