First principle understanding of antiferroelectric ordering in La-doped silver niobate

Abstract

The antiferroelectric Pbcm phase of silver niobate (AgNbO3) has received increasing attention owing to its environmental safety (as it is lead-free), compatibility, and superior energy-storage density compared with its ferroelectric counterparts. We comprehensively investigated the effects of La doping at Ag sites (i.e., Ag0.88La0.12NbO3) on the structural, electronic, and ferroelectric properties of AgNbO3 by using ab initio density functional theory calculations and the Berry phase method for polarization calculations, respectively. The polarization in the [001] direction of pristine AgNbO3 is estimated to be 1.9 μC/cm2, which is significantly enhanced (to 14.86 μC/cm2) for Ag0.88La0.12NbO3. The enhancement in the spontaneous polarization of AgNbO3 after the incorporation of La is attributed to suppressed distortion in the Nb–O–Nb antiparallel ordering and tilting of the NbO6 octahedra. Furthermore, the electron density maps of AgNbO3 and its doped counterpart were calculated to investigate the lattice-distortion and bond-change observations.