PHASE-DIAGRAMS OF THE CAF2-(Y,LN)F3 SYSTEMS .2. DISCUSSION

Earlier and new results of a study of CaF2-(Y,Ln)F3 systems are discussed. It is shown that the series of CaF2-LnF3 systems provides an interesting example of gradual change in phase diagrams upon successive replacement of one of the components by an analogous component from the periodic system. The variation of the limiting solubilities and the temperature stability of phases in the CaF2-LnF3 systems is also discussed. It has been shown that the main phases in the temperature range investigated are non-stoichiometric phases with statistical distributions of various valency cations on the positions of the fluorite and LaF3 structural types (the α-UO3-type solid solution is stable only at high temperatures). The nonstoichiometric Ca1-xLnxF2+x and Ln1-yCayF3-y phases are characterized by disordering of the anion sublattice. Such phases may be considered as solid solutions with a variable number of anions in the unit cell when the cation sublattices are fully occupied. © 1979.