Thermodynamic study of the solid–liquid equilibria in the MIPO3–Ce(PO3)3 systems (MI = Li, Na, K, Rb, Cs, Ag, Tl)

An equation of the liquidus curve of a stoichiometric phase has been established in a previous publication. In this work, the obtained formula is applied to the phase diagram determination of the MIPO3–Ce(PO3)3 (with MI=Li, Na, K, Rb, Cs, Ag, Tl) systems. The temperature, enthalpy and entropy of fusion are calculated for each solid phase with the exception of lithium and silver polyphosphates, of which crystallization fields were very limited. The enthalpy of fusion of all of these polyphosphates is determined from the DTA curves. The melting enthalpy of Ce(PO3)3, calculated from different binary systems is approximately equal to the measured value. The calculated temperatures and compositions are in good agreement with experimental determinations.