Origin of polar nanoregions in relaxor ferroelectrics: Nonlinearity, discrete breather formation, ge transfer

A central issue in the physics of relaxor ferroelectrics is the origin of the formation of polar nanoregions below some characteristic temperature scale. While it is often attributed to chemical disorder, random bond-random field appearance, or local symmetry lowering, it is shown here that the huge intrinsic nonlinearity of ferroelectrics gives rise to spatially limited excitations of discrete breather (DB) type, which interact strongly and self-consistently with the remaining lattice. This scenario corresponds to a two-component approach to relaxor physics with distinctive signatures in the dielectric spectra and strong charge-transfer effects. The theoretical results are compared to broadband dielectric spectroscopy on 0.2PSN-0.4PMN-0.4PZN ceramics, which provides clear evidence for the two-component scenario and the emergence of DB-like dynamics with decreasing temperature.