Light scattering and computational simulations of the superionic behaviour of CaF2 doped with lanthanide ions

High temperature Brillouin and Raman light scattering studies have been used to study the transition to the superionic state of CaF2 (10 mol%LaF3) and CaF2 (10 mol%TbF3) over the range 300 to 1200 K. The Brillouin scattering results yield the temperature dependence of the elastic constant C11. that undergoes a marked decresase above the transition temperature Tc while the Raman measurements of the width of the peak ay 310 cm–1 show a corresponding substantial broadening. The transition temperatures are ∼900 K in CaF2 (10 mol%LaF3) and ∼1000 K in CaF2 (10 mol%TbF3). Molecular dynamics simulations of fluorine diffusion in both systems closely reproduces the transition temperatures as well as the details of the higher temperature behaviour of the Brillouin and Raman signatures. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)