Mechanical stress in a dielectric solid from a uniform electric field.
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Mechanical stress in a dielectric solid from application of a uniform electric field is usually assumed to be described by ''Maxwell stress,'' proportional to the first power of the relative dielectric constant, kappa. Significant corrections are found from energy minimization when the dependence of permittivity on strain is included. Electrostriction coefficients are evaluated by the use of a model dielectric consisting of a simple-cubic lattice of linearly polarizable point dipoles. Compressive stress in the applied-field direction is larger than expected by more than a factor of kappa. The force density exerted on internal space charge needs to be corrected by the same factor. Stress components also have been calculated, with identical results, through direct summation of microscopic forces. This method permits identification of the origins of electrically induced stress. The dominant contribution is a compressive stress in the field direction, proportional to kappaS, from attraction between free charge at the electrodes. This component can attain tens of MPa at fields approaching the intrinsic dielectric strength. A lateral tensile stress independent of kappa also is present, which may assist electrical breakdown in some crystalline dielectrics. These stress components are augmented by short-range, dipolar forces throughout the bulk of the dielectric. Deformations more » accompanying poling of poly(vinylidene fluoride) are considered and found to be influenced by electrically induced stress. « less