ELECTRICAL AND OPTICAL-PROPERTIES OF MIXED AURIVILLIUS PHASE BI7TI4NBO21 SINGLE-CRYSTAL

Single crystals of the ferroelectric mixed Aurivillius phase Bi7Ti4NbO 21 have been prepared by the Aux method in Bi2O3 excess. Thermal depen dence of dielectric permittivity, X-ray diffraction patterns, birefrin gence and optical observations as well as differential scanning calori metry have been studied between room temperature and 900 degrees C. Tw o temperature driven phase transitions were observed, the first one cl ose to 630-675 degrees C within a ferroelectric state (ferro I-ferro I I), the second one at approximate to 830 degrees C, between the ferroe lectric state II and the paraelectric state.