Electrical and optical properties of mixed Aurivillius phase Bi7Ti4NbO21 single crystal

Single crystals of the ferroelectric mixed Aurivillius phase Bi7Ti4NbO21 have been prepared by the Aux method in Bi2O3 excess. Thermal dependence of dielectric permittivity, X-ray diffraction patterns, birefringence and optical observations as well as differential scanning calorimetry have been studied between room temperature and 900 degrees C. Two temperature driven phase transitions were observed, the first one close to 630-675 degrees C within a ferroelectric state (ferro I-ferro II), the second one at approximate to 830 degrees C, between the ferroelectric state II and the paraelectric state.