A first-principles model was developed in order to investigate the influence of Pb vacancies on the properties of the disordered Pb(Sc1/2Nb1/2)O3 ferro-electric. The Pb vacancies generated large inhomogeneous electric fields that reduced the barriers between energy minima for various polarization directions. This explained naturally why disordered ferro-electrics with significant Pb-vacancy concentrations had broadened dielectric peaks at lower temperatures, and why Pb vacancies smeared properties in the neighborhood of the ferro-electric transition in Pb(Sc,Nb)O3. The usual assumption, that vacancies reduced the magnitude of the dielectric response, was reconsidered.

Effects of Vacancies on the Properties of Disordered Ferroelectrics - a First-Principles Study. L.Bellaiche, J.Íñiguez, E.Cockayne, B.P.Burton: Physical Review B, 2007, 75[1], 014111 (5pp)