Dielectric-relaxation experiments on cubic solid solutions ofSrF2andCeF3orPrF3

Abstract

In this paper we report results of ionic-thermocurrent (ITC) and dielectric-loss experiments on solid solutions of the types ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Ce}}_{x}{\mathrm{F}}_{2+x}$ and ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}{\mathrm{F}}_{2+x}$. These solid solutions have the fluorite lattice structure and we have chosen $0\ensuremath{\le}x\ensuremath{\lesssim}0.3$. We have investigated the behavior of the dipole reorientation and the space-charge relaxation bands in the "ITC spectra." During the dielectric-loss experiments we have concentrated our attention on the dipole peaks. The experimental methods employed in this paper enable us to draw conclusions about the defect structure of the solid solutions. It appears that up to relatively high concentrations the defects present are primarily charge compensation centers (nearest-neighbor or next-nearest-neighbor dipoles). Clustering is relatively unimportant, which is in contrast with our recent results obtained for solid solutions of the type ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Yb}}_{x}{\mathrm{F}}_{2+x}$. This will be discussed in some detail. The space-charge relaxation peak, investigated in detail with the ITC method, shifts to lower temperatures with increasing concentrations of ${\mathrm{Ce}}^{3+}$ or ${\mathrm{Pr}}^{3+}$. This phenomenon is discussed and explained in terms of a percolation-type conduction model. In this model, jumps of interstitial fluoride ions in the close vicinity of trivalent impurity ions, which have a relatively small activation energy, play an essential role.