Finite-temperature properties of PbTiO3 by molecular dynamics simulations

PbTiO3 is a prototypical ferroelectric perovskite that is known to undergo a temperature driven ferroelectric tetragonal to paraelectric cubic phase transition, but the understanding of some key phenomena and associated mechanisms underlying this transition remains unclear. Here, using molecular dynamics simulations based on first-principles effective Hamiltonian, we show the behaviors of the phase transition temperature T-c and adiabatic temperature change Delta T of PbTiO3 under an external electric field and tensile stress along the [001] direction. Our results show that the electric field E induces rising T-c via a linear relation T-c proportional to 0.3083 E, rendering the phase transition to go from first-order with thermal hysteresis to second-order without thermal hysteresis above similar to 200 kV/cm; meanwhile, a maximum electrocaloric response Delta T-max similar to 34 K is obtained under E = 500 kV/cm. Moreover, external stress (sigma(z)) causes rising T-c via a linear relation T-c proportional to 160 sigma(z) and improves the electrocaloric response Delta T-max when combined with the electric field. The present results offer insights into the physical processes and mechanisms that dictate finite-temperature properties of ferroelectric perovskite oxides, laying a foundation for further exploration of this intriguing class of materials.