RAMAN-SCATTERING STUDY OF PHASE-TRANSITIONS IN RBCAF-3

Recent experiments on RbCaF3 have indicated the occurence of structural phase transitions at low temperature. The Raman data presented here confirm the transition at 200 K to be similar to the cubic-tetragonal transition occuring in SrTiO3 and KMnF3: soft modes of A1g and Eg symmetry are observed and the spectrum is consistent with D4h crystal symmetry. At 45 K the frequency and damping of the A1g mode begin to increase with further decrease in temperature, both of which suggest the the emergence of a new low-frequency mode of A1 symmetry at this temperature. © 1976