A Low‐Temperature Phase Transition in the One‐Dimensional Conductor K2Pt(CN)4Br0.30 ·x H2O

Abstract
It is shown that the linear superlattice distorsion of periodicity 6 × 2.88 Å, which was recently observed by X‐ray diffuse scattering in the one dimensional conductors of the type K2Pt(CN)4Br0.30 · x H2O, looses progressively its one‐dimensional character for temperatures lower than 120 °K. This seems to announce a phase transition at a temperature lower than 77 °K leading to a unit cell 3 c × 2 a × 2 a, referring to the room temperature parameters. It is suggested that this phase transition arises from the condensation of the lowest frequency longitudinal soft modes due to a giant “Kohn anomaly”.