New ferroelastic K2Sr(MoO4)2: Synthesis, phase transitions, crystal and domain structures, ionic conductivity

K2Sr(MoO4)(2) crystals were synthesized and their properties examined. The distortive polymorphic transformations at 421 K (alpha (LT) -> beta(MT)) and 744 K (beta(MT)->gamma (HT)) of K2Sr(MoO4)(2) were studied. It has been shown that the transitions go in sequence from the high-temperature palmierite K2Pb(SO4)(2)-type gamma-phase (R (3) over barm) to an intermediate beta-phase with a probable incommensurate structure and then to a low-temperature alpha-phase. Domain structures peculiarities in ferroelastic alpha-K2Sr(MoO4)(2) have been investigated. The electrical conductivity of K2Sr(MoO4)(2) rises tenfold in the vicinity of the phase transition at 744 K that may be associated with a change conductivity path from quasi-one-dimensional to two-dimensional. The crystal structure of the alpha-phase (sp. gr. C2/c, a=14.318(3) angstrom, b=5.9337(12) angstrom, c=10.422(2) angstrom, beta=105.83(3)degrees, Z=4, R=0.0219) is similar to that of alpha-Pb-3(PO4)(2). Sr atoms are mainly located at site with the coordination number CN=8 (a tetragonal antiprism with bond lengths of 2.578(2)-2.789(2) angstrom) and K atoms are located at site with CN=9+1. (C) 2016 Elsevier Inc. All rights reserved.