Properties of vacancy-rich ordered(A,[])Nb2O6perovskites

Abstract

Using first-principles calculations, we have investigated properties of the $(A,[]){\mathrm{Nb}}_{2}{\mathrm{O}}_{6}$ perovskite systems exhibiting a rocksalt ordering between divalent A atoms---$A=\mathrm{Ca},$ Sr, Pb, or Ba---and neutral vacancies [ ]. Their properties can be understood by simple rules and by analogy with the corresponding $A{\mathrm{TiO}}_{3}$ simple perovskites. Contrary to common belief, all the studied vacancy-rich systems exhibit ferroelectric instability. Furthermore, their ground state can be ferroelectric, antiferrodistortive, and may be sensitive to pressure or quantum effects, depending on the A atom.