Raman Scattering from the Soft Phonon in Sr₂Nb₂O₇ for the Phase Transition at 117 K

Abstract

Raman spectra of Sr₂Nb₂O₇ have been obtained between 45 K and 395 K. A low-lying mode observed at a(bc)\bara geometry softens toward the 117 K transition temperature and the square of the soft-mode frequency depends linearly on temperature on both sides of the phase transition. The soft mode remains underdamped in entire range of temperature studied.