Huang diffuse scattering of X-rays from the displacement field of hydrogen in niobium

The symmetry and strength of the displacement field of hydrogen interstitially dissolved in niobium has been determined by means of Huang diffuse scattering of X-rays (Mo K alpha 1 ). The measurements were performed at room temperature in the alpha phase of NbH x . Detailed measurements of the scattered X-ray intensity close to the (330) reciprocal lattice point yielded the following results: (i) The scattered intensity increased linearly with hydrogen concentration as predicted for isolated point defects; (ii) the displacement field has cubic symmetry, (iii) the double force tensor describing the long ranged displacement field is P ij = delta ij (3.37+or-0.1) eV.