The allotwinning of KCa3Te5O12Cl3: an OD interpretation

Abstract

Abstract The crystal structure of the oxotellurate(IV) chloride KCa3Te5O12Cl3 is built up of [KTe5O12]3− layers sandwiched by layers of Cl− and Ca2+ ions. The structure can be considered as a twelvefold superstructure with occupational modulation of the K/Te positions. The electron lone-pairs of the Te(IV) atoms are directed towards the free space of the chloride layers. KCa3Te5O12Cl3 can be described as a category III order-disorder (OD) structure in terms of polar layers of one kind. The crystals under investigation are built up of the two polytypes of a maximum degree of order (MDO) with isomorphic C2/c and I2/a symmetry, both of which appear in two orientations. Two data reduction approaches, using either a reciprocal superlattice or three independent domains, were performed and the resulting refinements are comparatively discussed.