Electrostriction

The term ferroelectricity is briefly introduced and the properties of the perovskite-structure mixed-oxide group are reviewed with special reference to BaTiO 3 . The distinction between piezoelectricity and electrostriction is explained in some detail, and the relevant expressions relating the electrical and mechanical properties are discussed for both the single crystal and ceramic specimens. It is pointed out that there is still considerable doubt as to the exact mechanism involved, especially in the case of the ceramics when electrical stresses are applied, and simplified models are discussed to demonstrate the factors contributing to the resultant strain. Single crystals are then discussed in detail, with a survey of the methods of growth and results of striction and hysteresis loop measurements; the most likely interpretation of these results is discussed. Similarly the more complicated ceramic materials are dealt with, and it is shown that measured values of the striction constants conform reasonably with theory, but further analysis is still needed to account for small discrepancies. Time dependent effects are also described and tentative explanations given. Brief mention is made of other oxide materials and possible directions of future research.