Structurally frustrated polar nano-regions in BaTiO3-based relaxor ferroelectric systems

BaTiO3-doped relaxor ferroelectrics (RF's) exhibit a broad frequency dispersive dielectric constant maxima at a "diffuse phase transition" temperature Tm and a slim P-E ferroelectric hysteresis loop. They have widespread applications as lead-free, electrostrictive and/or piezoelectric sensors and actuators as well as for the electrical field-tuneability of their dielectric properties. RF behaviour has long been attributed to the existence of polar nano regions (PNRs). The nature of these PNR's and their relationship to compositional heterogeneity, however, is still far from well understood. We have recently found direct experimental evidence for inherently polar, displacively disordered, 1-d PNR's in four different types of doped BaTiO3 RF compounds in the form of {001}* sheets of diffuse intensity. The role of the dopant ions in these RF systems appears to be to set up random local strain fields suppressing transverse correlations of these <001> chain dipoles and frustrating the development of long range ferroelectric order. Below the freezing temperature of the dipole dynamics, the application of a sufficiently large applied electric field aligns the 1 d PNRs and give rise to macroscopic spontaneous polarisation.