Giant electrocaloric response in the prototypical Pb(Mg,Nb)O$_{3}$ relaxor ferroelectric from atomistic simulations

TL;DR

This study uses atomistic simulations to reveal a giant electrocaloric response in Pb(Mg,Nb)O₃ relaxor ferroelectrics near a critical point, driven by field-induced nanoregion percolation, with results aligning with a Landau-like model.

Contribution

It demonstrates the microscopic origin of the giant electrocaloric effect in relaxor ferroelectrics near a critical point using atomistic simulations.

Findings

Giant electrocaloric response occurs near the critical point.

Electrocaloric response is driven by percolation of polar nanoregions.

Maximum EC coefficient correlates with specific dipole orientations.

Abstract

An atomistic effective Hamiltonian is used to investigate electrocaloric (EC) effects of Pb(Mg$_{1/3}$Nb$_{2/3}$)O$_{3}$ (PMN) relaxor ferroelectrics in its ergodic regime, and subject to electric fields applied along the pseudocubic [111] direction. Such Hamiltonian qualitatively reproduces (i) the electric field-versus-temperature phase diagram, including the existence of a critical point where first-order and second-order transitions meet each other; and (ii) a giant EC response near such critical point. It also reveals that such giant response around this critical point is microscopically induced by field-induced percolation of polar nanoregions. Moreover, it is also found that, for any temperature above the critical point, the EC coefficient-versus-electric field curve adopts a maximum (and thus larger electrocaloric response too), that can be well described by the general Landau-like model proposed in [Jiang et al, Phys. Rev. B 96, 014114 (2017)] and that is further correlated with specific microscopic features related to dipoles lying along different rhombohedral directions. Furthermore, for temperatures being at least 40 K higher than the critical temperature, the (electric field, temperature) line associated with this maximal EC coefficient is below both the Widom line and the line representing percolation of polar nanoregions.