X-ray scattering from Co0.83[Pt(C2O4]2]·6H2O: A system with two coupled order parameters

X-ray studies of the quasi-one-dimensional conductor Co0.83 [Pt(C2O4)2]·6H2O, Co(def)OP, show both a Peierls distortion with a period of 2k F = 1.70·2π/c and a separate (earlier reported) three-dimensional superlattice. The two distortions couple, so that the drastic decrease in electrical conductivity is accompanied by the occurence of the superlattice spots with a common critical temperature, T = (297 ± 4)K. The striking differences between Co(def)OP and Mg(def)OP are discussed and explained in terms of the different atomic structures of the cations.