Further observations on the effects of nonhydrostatic compression on the F_R1 → A_O polymorphic phase transformation in niobiumdoped, lead-zirconate-titanate ceramic

We recently performed a series of experiments on Nb-doped lead-zirconate-titanate ceramic to investigate the influence of constant shear stresses on the displacive, first-order rhombohedral/ferroelectric → orthorhombic/antiferroelectric polymorphic transformation. In a previous paper and report we demonstrated that increasing shear stresses lowers the mean stress and confining pressure at which the transformation occurs, but we did not identify a criterion by which the transformation could be predicted to take place under nonhydrostatic stress. In this paper we use the dielectric anomaly which accompanies the transformation as an indicator of onset of the transition, and correct for the effects of high-pressure-seal friction on measurement of the maximum compressive stress applied to the test specimens during deviatoric loading. We show that a convincing case can be made that the transformation occurs when the maximum compressive stress equals the hydrostatic pressure at which the transformation would otherwise occur.