Piezoelectricity of Quartz for Finite Strain

Abstract
In order to obtain an estimate of the maximum piezoelectric polarization possible for alpha quartz, the principal piezoelectric coefficient is calculated on the basis of a hard‐sphere, rigid‐ion model. The result, obtained by purely geometrical reasoning (including an ad hoc geometrical constraint), fits the measured value of e11 with an ``effective ionic charge'' of one‐sixth the free ionic charge. Extension of the calculation to finite compressive strain yields a maximum polarization of 3.4 μcoul/cm2 at a 34% strain. (Compare with e11=16.7 μcoul/cm2 per unit strain.) For higher strains the polarization drops off rapidly, but the model becomes inconsistent for strains greater than 43%. A test for more general validity of the model, by obtaining directly the ratio of the two independent piezoelectric coefficients, e14/e11, yields seven times the measured ratio.

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