Ferroelectric relaxor characteristics and phase transitions studied by thermal strain and optical methods

Thermal strain and optical birefringence measurements of ferroelectric materials reveal distinctively different physical phenomena, yet both are sensitive to polarization characteristics and ferroelectric phase transitions. These methods are particularly powerful in studying ferroelectric relaxor materials that are characterized by dynamic local polarization of micro or nano- dimensions, which are often. undetected by other characterization probes based on long range order (e.g., powder x-ray diffraction) or transport properties (e.g., static pyroelectric measurement). This paper gives a review based on author's work using these two complementary techniques in studying ferroelectric relaxor materials both of perovskite and tungsten bronze structures. Thermal expansion results from recent studies on single crystal high strain piezoelectric materials [Pb(Zn1/3Nb2/3)O-3(-) PbTiO3] are also reported in this paper, for which poling and boundary conditions are found to have significant effect on phase transition sequence and strain temperature