Spatial correlations in the valence of metal ions in Ni_1-xPd_x(chxn)₂Br₃

X-ray scattering experiments have been performed on a quasi-one dimensional system, Ni_1-xPd_x(chxn)₂Br₃. Strong diffuse scattering was observed for x > 0.7, and it was interpreted as due to spatial inhomogeneity in the valence of metal ions. This inhomogeneity takes the form of CDW in which the metal ions within a chain have valences alternating between +2 and +4. Correlations in the valence sequence could be determined parallel as well as perpendicular to the chain direction. Pair correlation functions deduced from the measurements show the existence of strong correlation between the positions of bridging Br ions and those of Br counter ions. It is concluded that the valence of metal ions for x < 0.7 is +3. These results are consistent with previous data on optical and magnetic measurements.