Synthesis, structures, physicochemical properties, and crystal-chemical systematics of M2IIAIIUO6 (MII = Pb, Ba, Sr; AII = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) compounds

Pb2AIIUO6 (AII = Mg, Ca, Sr, Ni, Zn, Cd) compounds were synthesized by high-temperature reactions in the solid phase. For the Pb2MgUO6, Pb2CaUO6, and Pb2CdUO6 compounds, the crystal structures (space group P21/n) were refined by the Rietveld method. It was demonstrated that these structures belong to the perovskite structure type. Crystal-chemical systematics was performed for all synthesized perovskites. High-temperature X-ray diffraction and differential scanning calorimetry were used to study the thermal stability and phase transitions, determine the thermal expansion coefficients, and elucidate the effect of atoms located in octahedral and cuboctahedral positions on the heating behavior of the structure. The standard enthalpies of formation of the Pb2AIIUO6 compounds were determined by reaction calorimetry.