Ferroelectric Transition of Sr5SmTi3Nb7O30 Tungsten Bronze Ceramics Investigated Using Differential Scanning Calorimetry and Raman Scattering

Ferroelectric transition of Sr5SmTi3Nb7O30 tetragonal tungsten bronze ceramics was investigated using dielectric characterization, differential scanning calorimetry (DSC), and the in situ Raman scattering. The first-order ferroelectric transition was indicated around 200 degrees C by the dielectric peak and the endothermic DSC peak on heating. The ferroelectric transition exhibited large thermal hysteresis and severe depression of the CurieWeiss temperature (T0), where the transition peak did not show up on cooling in both the permittivity and DSC curves. The thermal hysteresis was attributed to the complex nature of the tungsten bronze structure. According to the DSC results, gradual recovery of the endothermic peak occurred after aging at 20 degrees C, indicating the gradual stability of the ferroelectric phase after cooling from the high temperature paraelectric phase. Meanwhile, anomalies in the Raman spectra were also observed around 200 degrees C, corresponding to the ferroelectric transition. Mechanism of the ferroelectric transition in Sr5SmTi3Nb7O30 ceramics was discussed according to the variation of the external and internal Raman modes with increasing temperature.