Linear chain structure in cubic KNbO3 and BaTiO3

Both KNbO3 and BaTiO3 systems, in their cubic, tetragonal or orthorhombic phases, were reported to show two-dimensional (2D) diffuse scattering intensity sheets in the reciprocal space, thus indicating the presence of one-dimensional correlation in the real space. Two models have been proposed to explain the origin of the diffuse intensities: 1) static chain model by Comes, Lambert and Guinier, and 2) dynamical model by Huller. The current investigation presents some new results regarding the anomalous 2D diffuse scattering sheets. High-resolution synchrotron x-ray measurements have been undertaken to resolve fine features in the 2D diffuse intensity distribution at several temperatures above the Curie point. Intensity profile fittings and simulations have been performed to test against the two models. Our results support the concept put forth by Huller which is based upon a shallow, soft phonon mode. This paper, however, does not address the physical mechanism governing the structural transformations in these two systems.