First Principle Understanding of Antiferroelectric Ordering in La-Doped Silver Niobate

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 of 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 AgNbO 3 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