Structural properties of Sr{sub 0.61}Ba{sub 0.39}Nb{sub 2}O{sub 6} in the temperature range 10-500 K investigated by high-resolution neutron powder diffraction and specific heat measurements

We report high-resolution neutron powder diffraction on Sr{sub 0.61}Ba{sub 0.39}Nb{sub 2}O{sub 6} 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 NbO{sub 6} 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 T{sub c}{approx_equal}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.