First Order FE-AFE Phase Transitions in LiTaO₃/LiNbO₃ through Electric Boundary Conditions

Ferroelectric (FE) materials exhibit spontaneous electric polarization that arises below the Curie temperature, where ionic displacements break crystal symmetry, leading to a net dipole moment from aligned atomic dipoles. This polarization is switchable under an applied electric field, enabling applications in non-volatile memory devices. In contrast, antiferroelectric (AFE) materials feature antiparallel dipole alignments, resulting in zero net polarization, which is advantageous for high-energy-density storage capacitors due to their double hysteresis loops and large recoverable energy.

This computational study examines LiNbO₃ and LiTaO₃, prototypical FE materials that can transition to an AFE phase under specific electric boundary conditions. Under short-circuit boundary conditions (SCBC), the depolarization field generated by spontaneous polarization is compensated by surface charges, stabilizing the FE phase. Under open-circuit boundary conditions (OCBC), the uncompensated depolarization field persists, typically driving traditional ferroelectrics toward a centrosymmetric paraelectric state with suppressed polarization. However, in LiNbO₃ and LiTaO₃, this field induces a first-order transition to a non-centrosymmetric AFE phase characterized by alternating dipole orientations.

Employing density functional theory (DFT) simulations, we model these materials under varying electric boundary conditions to characterize the phase transition energetics, structural changes, and critical field strengths. Our findings provide insights into controlling the FE-AFE switching, with potential implications for tunable dielectric devices and energy harvesting technologies.