Thermal conductivity measurement of poled and unpoled relaxor ferroelectric PMN-30PT

Polarization caloritronics is an expanding field dedicated to exploring thermal fluctuations in the polarization of ferroelectric materials. Wooten et al. [1] reported the electric field dependence of sound velocity, thermal conductivity and thermal diffusivity in Pb(Zr,Ti)O₃ (PZT), confirming the role of changes in the phonon dispersion with polarization in this material. This research was further extended by Rashadfar et al. [2] to the ferroelectric relaxor (PMN-33PT), where they uncovered a relationship between sound velocity changes and thermal conductivity with an applied electric field. These effects are interpreted quantitatively and without adjustable parameters by using known material properties: the piezoelectric coefficients (d₃₃ and d₃₁) and the Grüneisen parameter (γ). Previous neutron scattering data on PMN-30PT [3] also reveal significant softening in the lower part of the transverse acoustic (TA) phonon branch and a notable reduction in phonon lifetime, probably due to the increased phase space for phonon scattering. Here we report on the thermal conductivity of PMN-30PT along the (001), (100), and (011) crystallographic orientations for both poled samples along the (001) axis and unpoled samples. The changes due to poling are of the order of a factor of 2 and are not linked to domain wall scattering but rather to alterations in the sound velocities and the phase space available for acoustic phonon scattering due to electric field-induced changes in the phonon spectrum. While we do not yet report on dynamic measurements in field, the magnitude of the difference between poled and unpoled samples in the specified orientations suggests that this effect could be the base for electrically actuated heat switches with a practical switching ratio.

[1] Science Advances 9, eadd7194 (2023)

[2] D. Rashadfar, et al. ArXiv 2402.08516

[3] Science Advances 2, e1501814 (2016)