Thermal Evolution of Phosphates and Sulfates with Antiperovskite Structure Type (The Thermal Expansion Features and Phase Transitions)

The thermal behavior of natural and synthetic phosphates and sulfates with an antiperovskite structure type, where the anion-centered octahedron is the main structural unit, is investigated. Herein, we discuss the examples of thermal behavior of antiperovskites with the classical and hexagonal 3D frameworks (K3SO4F, Rb3SO4F, synthetic analogue of kogarkoite, Na3SO4F, galeite, Na15(SO4)5ClF4, and schairerite Na21(SO4)7ClF6), with 1D chains of corner- and face-sharing octahedra (nacaphite, Na2CaPO4F and its synthetic dimorph, synthetic analogue of moraskoite, Na2MgPO4F, and nefedovite, Na5Ca4(PO4)4F), and with clusters in the form of trimers of anion-centered octahedra (synthetic analogue of arctite (Na5Ca)Ca6Ba(PO4)6F3). Using the data obtained, some general patterns of the thermal expansion in dependence of the structural topology and thermal stability of antiperovskites were established.