X-ray scattering study of one-dimensional lattice dynamics in ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$

The diffuse scattering of x rays by the linear chains of Hg atoms in the quasi-one-dimensional compound ${\mathrm{Hg}}_{3-\delta }\mathrm{As}{\mathrm{F}}_6$ was studied at temperatures from 100 to 350 K, and wave vectors from 7 to 20 ${\mathrm{\AA }}^{-1\mathrm{}}$. The results are consistent with thermal diffuse scattering from a disordered one-dimensional "liquid" and, at high temperatures, agree quantitatively with the model of classical, independent, harmonic chains proposed by Emery and Axe. Deviations are observed in the temperature region from 130 to 200 K where the correlation length is about 25% longer than predicted.