Dielectric Parameters for Electrostriction of Solids

Some polymer films exhibit large electrostrictive deformations in an electric field, greater than the piezoelectric deformations of inorganic materials. These materials can be exploited in such devices as transducers, actuators, and sensors. Selecting suitable materials for practical applications requires knowledge of the relationships between material composition and the properties that govern electrostriction. Electrostriction is governed by dielectric parameters that describe the the linear relationship between the dielectric tensor (ɛ_ij) and the strain tensor (u_ij), ɛ_ij=ɛ^0 δ_ij+ a₁ u_ij+ a₂ u_kk δ_ij. The dielectric parameters a₁ and a₂ govern the magnitude of electrostrictive deformation; however, these parameters have not been measured for many systems, and their dependence on chemical composition is not known. In this presentation, we discuss a new experimental technique to measure these parameters, as well as a microscopic model that relates them to other material properties of isotropic amorphous or crystalline materials. Experimental data and model predictions show that a₁ and a₂ are more important than the dielectric constant (ɛ^0) in controlling electrostatic forces and electrostrictive deformation. Thus, these material parameters are of practical importance, as well as theoretical interest for the general problem of electrostatic forces in materials.