Structurally frustrated polar nanoregions in BaTaO₂N and the relationship between its high dielectric permittivity and that of BaTiO ₃

This letter presents direct evidence for the existence of the same inherently polar one-dimensional (1D), displacive disorder in BaTa O2 N as occurs in paraelectric BaTi O3 as well as in doped BaTi O3 relaxor ferroelectric systems. The inherently polar, off-center and oppositely directed displacements of Ta and neighboring ON ions along 〈001〉 give rise to 1D polar nanoregions (PNRs) and are responsible for the dielectric properties of BaTa O2 N. A bond valence sum analysis of the underlying crystal chemistry of BaTa O2 N shows clearly that ON ordering is not directly responsible for inducing the observed 1D PNRs.