Ternary crystals Sr1−y Eu y−x 2+Eu x 3+F2+x of fluorite phases with a variable europium valence and their thermal conductivity (50–300 K)

Abstract

Crystals of new fluorite materials: ternary nonstoichiometric Sr0.9Eu0.086Eu0.014F2.014 and Sr0.5Eu0.432Eu0.068F2.068 phases with a structure of fluorite (CaF2) type, containing europium ions in different oxidation states (Eu2+, Eu3+), have been grown for the first time from a melt by the Bridgeman method. The variation in their thermal conductivity k(T) in a temperature range of 50–300 K has been experimentally studied. The equivalent cation positions with a large difference in cation masses (m Sr = 87.62 amu and m Eu = 151.96 amu) lead to low k(T) values of ternary (Sr1-yEuy-x 2+Eux 3+F2+x) and binary (Eu0.864 2+Eu0.136 3+F2.136) crystals. One can obtain crystals with thermal characteristics specified in a wide range by adjusting the ratio of strontium and europium (regardless of the valence). Since the thermal conductivity of Sr0.5Eu0.432Eu0.068F2.068 and Eu0.864Eu0.136F2.136 is independent of temperature in the range of 200–300 K, they can be recommended as reference materials with k(T) = const.