Synthesis, structures, physicochemical properties, and crystal-chemical systematics of M 2II AIIUO6 (MII = Pb, Ba, Sr; AII = Mg, Ca, Sr, Ba, Mn, Fe, Co, Ni, Cu, Zn, Cd, Pb) compounds

Pb₂A^IIUO₆ (A^II = 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 Pb₂A^IIUO₆ compounds were determined by reaction calorimetry.