Studies On Crystal Structure Phase Transitions And Dielectric Properties Of 1 X Bi Mg W O Xpbtio Ceramics

Abstract

newline Piezoelectricity is the Property of certain crystalline materials to develop electric charges by the application of external mechanical stress and strain on application of electric field [Jaffe et al. (1971)]. Nowadays, a large number of piezoelectric materials are used as sensors and actuator devices, which are used in aircraft, aerospace, automotive, medical imaging, ultrasonic and telecommunication devices [Jaffe et al. (1971), Turner et al. (1994), Shrout et al (2004)]. Most of the piezoelectric ceramics are derived from ferroelectric ceramics by poling at high dc- electric field to introduce anisotropy and piezoelectricity. The ferroelectric materials exhibit spontaneous polarization (P) which can be switched into crystallographically equivalent directions by an external applied electric field (E). Therefore, it possesses a P-E hysteresis loop. The hysteresis loop disappears above the Curie temperature (TC). It has domain structure, and high dielectric permittivity rising to a peak at the Curie temperature. The falling-off of its dielectric permittivity above the Curie temperature follows a Curie-Weiss law. The ferroelectric transition from a high symmetry paraelectric state to lower symmetry ferroelectric state is characterized by the appearance of spontaneous polarization at the phase transition temperature [Schmid (1994)].