Low Temperature Elastic and Dielectric Properties of Incommensurate Barium Sodium Niobate.

摘要

We have performed dielectric and Brillouin spectroscopic measurements on incommensurate (IC) Ba2Na Nb5O12 from ca. 15 K to room temperature and have related our measurements to earlier studies of birefringence and x-ray and neutron crystallography, with special emphasis upon the structural phase transition near 105 K and 40 K. The 105 K transition is from Ccm2(1) to a modulated structure, which appears to be a reentrant phase also found at atmospheric pressure from 565 K to 582 K. Such a reentrant IC/C/IC sequence is predicted in the phenomenological theory of Ishibashi. The lock-in phase below 40 K is tetragonal and probably of space group P4nc (structural refinements of preliminary neutron scattering data are in progress). (RRH)