The thermal vibrations and the fluorine ionic conductivity in LaF3

Abstract

Abstract The LaF3-structure has been reinvestigated using diffraction data measured with twinned crystals. LaF3 is a fluorine ion conductor with essentially 3-dimensional conductivity. The conduction perpendicular to the c-axis is shown to occur on pathways which include all three sets of fluorine positions in the structure. These pathways connect symmetrically non-equivalent nearest neighbour positions only. This conclusion is supported by the determination of anharmonic temperature factors. The temperature dependence of the harmonic Debye-Waller factors indicates that thermal vibrations are described rather than static discorder. The magnitude of the temperature parameters of fluorine is consistent with an intrinsic activation energy of 0.8 eV for fluorine conduction.