Thermodynamic properties of the MZr2(PO4)(3) (M=Na, K, Rb or Cs) compounds

The enthalpies of the solution of MZr2(PO4)(3) (M=Na, K, Rb or Cs) compound s have been measured by the help of a differential automatic isothermal Cal vet calorimeter and the standard enthalpies of formation have been derived. The temperature dependencies of the standard heat capacity of the samples of crystalline NaZr2(PO4)(3) and CsZr2(PO4)(3) were studied between 7 and 3 40 K in an automatic adiabatic vacuum calorimeter. The main thermodynamic f unctions H-0(T)-H-0(0), S-0(T) and G(0)(T)-H-0(0) have been determined. The Gibbs energies of formation of the NaZr2(PO4)(3) and CsZr2(PO4)(3) at 298. 15 K were calculated on the basis of these experimental data and the enthal py of formation data. Qualitative explanations for the results observed wer e presented.