Antiferroelectric Order of NO₂-Groups and Two Dimensional Nature of Phase Transition in K₂Ba(NO₂)₄

Abstract

The phase transition of K₂Ba(NO₂)₄ at T_c=−74°C has been investigated by X-ray diffraction. In the low-temperature phase (T<−74°C), superlattice reflections are observed at body center positions (h+1⁄2, k+1⁄2, l+1⁄2). In this phase, we find antiferroelectric order of NO₂-groups. Diffuse scattering above T_c is found to be anisotropic. It is suggested that the transition has two-dimensional nature.