Low frequency vibrational modes in Ba2 NaNb5 O15

Abstract
We have measured the Raman spectra of Ba2 NaNb5 O15 at temperatures from liquid nitrogen to 570°C. In the x(zzy scattering configuration a heavily damped mode was identified; and, its temperature dependence was sufficient to account for the dielectric anomaly found in this material. It is concluded that Ba2 NaNb5 O15 has a 'soft' A, vibrational mode as expected, but in contrast with the E mode which is 'soft' in BaTiO3.