Transport properties of fluorite-type solid solutions in the KF–BiF3 and PbF2–МF−BiF3 systems (M = K, Cs) studied by 19F NMR and conductivity measurements

Transport properties of fluorite-type xKF−(100 − x)BiF3, 50PbF2−(50 − y)BiF3−yKF and 66PbF2−17BiF3−17CsF solid solutions (30 ≤ x ≤ 45; y = 20, 25 mol%) were studied by 19F NMR spectroscopy and conductivity measurements. The observed transformations of NMR spectra in the range 150–450 K are caused by continuous change in the character of ionic mobility in the fluoride sublattice depending on the temperature, namely from ion vibrations in the rigid lattice through local motions to translational diffusion of fluoride ions. The characteristic temperature of fluoride subsystem transition from motionless state to dynamical one is determined by the sample composition. The 19F NMR data agree qualitatively with the results of conductivity measurements. It was found that diffuse phase transition proceeds in some KF–BiF3 solid solutions in the temperature range of 400–450 K. Samples with x = 40 and y = 20 have the highest ionic conductivity about 10− 2 S/cm at 500 K.