Pretransitional diffuse neutron scattering in the mixed perovskite relaxorK1-xLixTaO3

Several previous studies of K1-xLixTaO3 (KLT) have revealed the presence, a bove the structural transition, of polar nanoregions. Recently, these have been shown to play an essential role in the relaxer behavior of KLT. In ord er to characterize these regions, we have performed a neutron-scattering st udy of KLT crystals with different lithium concentrations, both above and b elow the critical concentration. This study reveals the existence of diffus e scattering that appears upon formation of these regions. The rodlike dist ribution of the diffuse scattering along cubic directions indicates that th e regions form in the shape of discs in the various cubic planes. From the width of the diffuse scattering we extract values for a correlation length or size of the regions as a function of temperature. Finally, on the basis of the reciprocal lattice points around which the diffuse scattering is mos t intense, we conclude that the regions have tetragonal symmetry. The large increase in Bragg intensities at the first-order transition suggests that the polar regions freeze to form large structural domains and the transitio n is triggered by the percolation of strain fields through the crystals.