ISSN 1023-1935, Russian Journal of Electrochemistry, 2011, Vol. 47, No. 6, pp. 639–642. © Pleiades Publishing, Ltd., 2011. Published in Russian in Elektrokhimiya, 2011, Vol. 47, No. 6, pp. 683–686. 639 INTRODUCTION In this paper, we study a dependence of the fast flu- oride ion conductivity, static permittivity, and thermal diffusivity on homovalent cationic substitutions in flu- orite-structured fluorides of the MF 2 –RF 3 (M = Ca, Sr, Ba; R = La, Ce, Pr, Nd, Gd, Tb) system. A partial homovalent substitution of both alkali earth and rare earth cations is examined. As to keep a constant con- centration of charge compensating defects, heterova- lent doping with a fixed total concentration of RF 3 is used. Up to 350°С, the fastest ionic transport was observed for Ba 0.35 Sr 0.35 La 0.3 F 2.3 single crystal. How- ever, its ionic conductivity is comparable with those of Ba 0.7 La 0.3 F 2.3 or Sr 0.7 La 0.3 F 2.3 single crystals [1, 2]. EXPERIMENTAL DETAILS Rare-earth fluorides and strontium fluoride of 99.9% purity, and optical grade CaF 2 and BaF 2 single crystals are used as starting reagents. They are melted under fluorinating atmosphere of Teflon pyrolysis products. Ba 0.75 La 0.25 – x Nd x F 2.25 , Ba 0.7 – x Sr x La 0.3 F 2.3 and Ba 0.35 Sr 0.35 (R 1 , …, …, R i ) 0.3 F 2.3 (i = 1–6; R i = LaCe, Pr, Nd, Gd, Tb, in equimolar concentrations) single crystals are grown from the melt using Bridgman tech- nique in graphite crucibles under fluorinating atmo- sphere. Transparent Ca 0.85 – x Sr x Nd 0.15 F 2.15 polycrystals are solidified in graphite crucibles in Ar atmosphere. The fluorite structure of crystals is confirmed by X-ray powder analysis. Chemical composition of sam- ples is checked using the concentration dependence of the lattice parameter [3]. Electrical properties are measured in dry Ar, at >50–650°C, and 1 Hz–1 MHz, both at a heating rate of 2°C/min and under isothermal conditions. Painted graphite and/or silver contacts and Solartron- Schlumberger 1260 are used. Dc conductivity, σ, and relative static permittivity, ε s , are calculated using the impedance or modular analyses, respectively. Thermal diffusivity, D T , is measured using the flash method [4] at room temperature. Samples are covered with a thin gold layer to ensure the opacity, and are blackened with colloidal graphite which absorbs the flash pulse. RESULTS Mixing of Alkali Earth Ions Ba 0.7 – x Sr x La 0.3 F 2.3 single crystals. From the point of view of fast ionic conductivity, heterovalent doping Ionic Conductivity of Multicomponent Fluorite-Structured Fluorides 1, 2 V. Trnovcová a, z , P. P. Fedorov b , I. I. Buchinskaya c , and M. Kubliha a a Department of Physics, Faculty of Materials Science and Technology, Slovak University of Technology, SK-917 24 Trnava, Slovakia b Institute of General Physics, Russian Academy of Sciences, Moscow, 119991 Russia c Institute of Crystallography, Russian Academy of Sciences, Moscow, 117333 Russia e-mail: viera.trnovcova@stuba.sk Received June 23, 2010 Abstract—Influence of mixing of homovalent cations on the fast anionic conductivity, static permittivity, and thermal diffusivity is investigated in multicomponent fluorite-structured concentrated solid solutions of alkali earth and rare earth fluorides. Influence of mixing of alkali earth cations on electrical properties of flu- oride superionics is studied in Ba 0.7 – x Sr x La 0.3 F 2.3 single crystals and Ca 0.85 – x Sr x Nd 0.15 F 2.15 transparent polycrystals. Influence of mixing of rare earth cations on electrical properties of fluoride superionics is studied in Ba 0.75 La 0.25 – x Nd x F 2.25 and Ba 0.35 Sr 0.35 (R 1 , …, R i ) 0.3 F 2.3 (i = 1–6; R i stands for rare earth elements) single crystals. It is shown that the ionic conductivity decreases with increasing difference between mean ionic radii of rare earth and alkali earth cations. Up to 350°C, the fastest ionic conductivity is found in Ba 0.35 Sr 0.35 La 0.3 F 2.3 single crystals. Keywords: multicomponent fluorides, fluorite structure, rare earth—alkali earth fluorides, ionic conductivity, static permittivity, thermal diffusivity DOI: 10.1134/S1023193511050144 1 Based on the paper presented at the X Meeting “Fundamental Problems of Solid State Ionics”, Chernogolovka (Russia), 2010. 2 The article is published in the original. z Corresponding author: viera.trnovcova@stuba.sk (V. Trnovcová).