Microscopic density fluctuations of deuterium in niobium

Density fluctuations in metal-hydrogen systems modulate the metallic host lattice. It is shown that this effect can be studied by Huang diffuse scattering of X-rays and neutrons. Measurements on deuterium interstitially dissolved in niobium are reported. The temperature dependence of the diffuse scattered intensity shows a mean-field behaviour with spinodal temperatures which agree well with predictions from the theory of elastic interaction. Possible explanations for the discrepancy between our results and those from small-angle neutron scattering are discussed. (author)