Abstract
To date, the effects of hydrostatic pressure on the polarization, dielectric constant, dielectric loss, and transition temperature of many perovskite-structured ferroelectrics have been reasonably well investigated (see, for example, Samara [1] for a review). For all of these investigations, however, the pressure was generated with fluid-media hydrostatic-pressure systems. Because the applied pressure is truly hydrostatic, experiments of this type are extremely valuable since they explain ferroelectric behavior in a straightforward, tractable, experimental situation. However, for a geophysicist interested in the behavior of a ferroelectric (FE) material in a planetary interior [2,3], experiments of this type are insufficient. Ferroelectric phases existing in planetary interiors with a considerable mechanical strength would have to comply with quasi-hydrostatic stress conditions and constraints set up by deviatoric stresses and strains. Exactly this type of environment is met in high-pressure experiments when a solid medium is used for the transmission of pressure [4]. Thus, in planetary interiors and in the case of solid-media, high-pressure experiments alike, the FE material forms an elastically and dielectrically inhomogeneous inclusion (transforming inclusion) [5] in a nonferroelectric matrix. In this case, due to the presence and consequent constraint of the surrounding (matrix) material, individual FE crystals are not entirely free to develop the full spontaneous strain associated with the polarization at the transition. Thus, transitions occurring in the FE inclusion are accompanied by self-stressing. From thermodynamic considerations, it is evident that in this case one has to account for contributions to the total free energy from terms related to both crystal and matrix, as well as their mutual interactions and interactions with the applied stress field.
Published Version
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