Complex Phosphates, Containing Elements with Oxidation Degrees +1 and +4

Crystal-chemical approach provided the scientific basis for the design of new compounds with a desirable structure and properties. In the present investigation we generalized and systematized our and literature data on synthesis, structures, thermal and physical characteristics of double and more complex anhydrous phosphates containing M+ and M4+ cations (M+ – H, NH4, Li, Na, K, Rb, Cs, Cu, Ag, Tl; M4+ – Ti, Zr, Hf, U, Th, Np, Pu). In order to study the influence of M+ and M4+ cationic radii on the stability regions of different structural types, we investigated the phase formation in the M1-x+Mx’+M24+(PO4)3 systems (M+, M’+ – Li, Na, K, Rb, Cs; M4+ – Ti, Zr, Hf) with smoothly varying compositions. The compounds and solid solutions were studied using an X-ray diffraction technique (using Rietveld method of structure refinement), electron microprobe analysis, IR-spectroscopy, adiabatic calorimetry (in the range 6−320 K) and differential scanning calorimetry (in the range 300−650 K).