High temperature raman scattering studies of Ba1-xLaxF2+x

Abstract In this study we investigate the superionic behaviour in Ba1-xLaxF2+x (x = 0.2, 0.3 and 0.5, respectively) over a range of temperatures using Raman scattering. The line-widths of the Raman peaks show a linear increase with temperature but above a certain temperature (T c) they start to increase more rapidly. The line-widths for pure BaF2, Ba0.7La0.3F2.3 and Ba0.5La0.5La2.5 show a marked increase above temperatures (T c) of 1150, 950 and 930 K, respectively. These results are compared with the work done on samples doped with relatively low concentrations of La3+ ions. Another interesting feature is that the Raman line shifts to the higher energies with increasing dopant concentration, being at 241, 263, 275 and 286 cm−1 for pure BaF2 and for samples in which x = 0.2, 0.3 and 0.5, respectively. The results are discussed in relation to the previous experimental and theoretical studies.