Electric field dependent thermal conductivity on ferroelectrics and beyond:Study on polarization waves in electrostrictive materials

Polarization caloritronics is a new field that studies the nature of the thermal fluctuations of polarization in ferroelectrics. A recent theoretical paper [1] introduces the concepts of polarization currents and the dependence of the thermal conductivity of ferroelectric solids on applied external electric fields. In previous work [2], which will be briefly reviewed in this talk, we showed the latter effect experimentally in a polycrystalline displacement ferroelectric, and that the applied thermal gradient alters the phonon density of states, resulting in a sizeable difference in thermal conductivity in field. We then developed a theory that ascribes the effect to heat transport by acoustic phonons affected by both electrostriction and anharmonicity. Here we present a new experimental investigation of that conclusion by providing thermal conductivity and resonant ultrasound spectroscopy data on single crystal ferroelectric 0.66Pb(Mg_1/3Nb_2/3)O₃ – 0.33PbTiO₃ (commonly referred to as PMN-PT) in an applied electric field. We compare the results to other electrostrictive materials such as SrTiO₃ and BaTiO₃ to test the boundaries of this theory. To quantify the effects of polarization on thermal properties, we compare the values of k'/k and v'/v, where k is thermal conductivity and v is the longitudinal acoustic phonon velocity, and the prime denotes the derivative of those quantities with respect to electric field.

[1] Phys. Rev. Lett. 126, 187603 (2021)

[2] Wooten et al., unpublished.