Depolarization experiments on space charges in concentrated solid solutions of NdF3in SrF2

Abstract

The influence of the defect concentration on the relaxation of space charges in ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ solid solutions has been investigated with the ionic-thermocurrent technique. A concentration domain of 0.004 up to 45 mol% has been used. As in the system ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$ the space-charge relaxation band (high-temperature band) shifts to lower temperatures with increasing $R{\mathrm{F}}_{3}$ concentration. A percolation model has been used to explain these shifts. Most of the differences between the systems ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ and ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$ are reducible to different dipolelike jumps supporting the charge transport: nearest-neighbor dipolelike jumps in ${\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{Nd}}_{x}{\mathrm{F}}_{2+x}$ and next-nearest-neighbor dipolelike jumps in ${\mathrm{Ba}}_{1\ensuremath{-}x}{\mathrm{La}}_{x}{\mathrm{F}}_{2+x}$. The charge transport may be interpreted qualitatively with a percolation mechanism.