Temperature and compositional dependences of the anionic conductivity, from ambient to 1073K, were studied for single crystals of Ca1−xGdxF2+x (x = 10−4, 10−3, 10−2 or 10−1) and of Ca0.8R0.2F2.2 (R = La, Ce, Pr, Nd, Gd, Dy, Er, Tm, Yb, Lu or Y), with a fluorite structure. Conductivity plots for concentrated Ca0.8R0.2F2.2 solid solutions exhibited linear low-temperature and high-temperature Arrhenius plots with a knee temperature, Tk, of about 770K. The values of the conductivity activation enthalpies obeyed the relationship: ΔHHT(T>Tk) > ΔHLT(T<Tk). The conductivity mechanism in heavily doped Ca1−xRxF2+x crystals was associated with clusters of point defects which decreased the potential barriers to fluoride anions moving by hops over the structural sites of the anion sub-lattice. A study was made of the effect of the dimensional factor (doped cation radii) upon anionic transport.

Anionic Conductivity and Thermal Stability of Single Crystals of Solid Solutions Based on Calcium Fluoride. N.I.Sorokin, M.W.Breiter: Solid State Ionics, 1999, 116[1-2], 157-65