Study of Thermal Transformations of Double Phosphates of Rare Earth Elements and Alkali Metals of Composition MILn(PO3)4 by the Raman Scattering Method.

A study of thermal transformations of the double phosphates M**I Ln(PO//3)//4 by the Raman scattering method in a wide temperature range showed that they melt incongruently, precipitating crystalline Ln(PO//3)//3. The peritectic-decomposition and liquidus temperatures of eight compounds of composition M**ILn(PO//3)//4 have been determined. During heating of the cyclotetraphosphates RbLaP//4O//1//2 and CsLaP//5O//1//2 obtained in polyphosphoric acid melt solutions irreversible phase transformations in the crystalline state of type C yields A for RbLaP//4O//1//2 and type C yields VI for CrLaP//4O//1//2 have been observed. The special features of the crystallization of the glasses obtained by melting M**ILn(PO//3)//4 have been ascertained.