Rotational instability of the electric polarization and divergence of the shear elastic compliance

TL;DR

This paper investigates the rotational instability of electric polarization during ferroelectric phase transitions, linking it to large piezoelectric responses and shear compliance divergence, with theoretical analysis and experimental verification on BaTiO3 and other ferroelectrics.

Contribution

It extends the theoretical understanding of polarization rotation effects on shear compliance divergence to general cases, including monoclinic phases, supported by experimental data.

Findings

Divergence of shear compliance is linked to polarization rotation during phase transitions.

Experimental elastic response measurements on BaTiO3 support theoretical predictions.

The approach applies to various ferroelectric perovskites like KNN.

Abstract

The rotational instability of the electric polarization P during phase transformations between ferroelectric phases is of great practical interest, since it may be accompanied by extremely large values of the piezoelectric coefficient, and a divergence of the coupled shear compliance contributes to such enhancements. In the literature, this had been explicitly calculated in the framework of the Landau theory and discussed with specific numerical simulations involving tetragonal, orthorhombic and rhombohedral ferroelectric phases. When monoclinic phases are involved, such an approach is practically impossible, and an approximated treatment had been proposed, based on the observation that in those cases there are shear strains almost linearly coupled to the transverse component of P, implying a divergence of the Curie-Weiss type in the associated compliances. Here the argument is extended to the general case of transitions whose major effect is a rotation of the polarization, and the limits of its validity are discussed. As experimental verification, the elastic response of BaTiO3 is measured and analyzed, together with those of other ferroelectric perovskites available in the literature, like KNN.