Structural properties of Sr0.61 Ba0.39 Nb2 O6 in the temperature range 10-500 K investigated by high-resolution neutron powder diffraction and specific heat measurements

Abstract

We report high-resolution neutron powder diffraction on Sr0.61 Ba0.39 Nb2 O6 in the temperature range 15-500 K. The results indicate that the low-temperature anomalies (T≤100 K) observed in the dielectric dispersion are due to small changes in the incommensurate modulation of the Nb O6 octahedra, as no structural phase transition of the average structure was observed. This interpretation is supported by specific heat measurements, which show no latent heat, but a glass-like behavior at low temperatures. Furthermore, we find that the structural changes connected with the ferroelectric phase transition at Tc 350 K start already at 200 K, explaining the anisotropic thermal expansion in the temperature range 200-300 K observed in a recent x-ray diffraction study. © 2006 The American Physical Society.