Electrostriction measurements on low permittivity dielectrics

The evaluation of electrostrictive properties of low permittivity dielectrics requires extremely sensitive instrumentation. In the present work, a modified compressometer for resolving fractional changes in capacitance on the order of 10^-6 is used, along with a modified single beam interferometer capable of subangstrom resolution in displacement. For the compressometric method, a high sensitivity capacitance bridge, GenRad 1615, is coupled with two lock-in amplifiers to detect attofarad (10^-18F) level capacitance changes caused by in-phase cyclic uniaxial stresses on samples. The interferometer is a Michelson-Morley type instrument modified to detect changes in interference fringe intensity for very small changes in path length. The measurements confirmed by both techniques are used to establish a set of reliable and accurate data of electrostriction coefficients for low permittivity materials. Using these recent data, along with widely accepted data on ferroelectric materials and soft polymers, the linear relationship between electrostriction coefficient (Q) and the ratio of elastic compliance over dielectric permittivity (s/ε₀ε₁) is obtained. This leads to an effective way to predict the electrostriction coefficient in dielectric materials