X‐ray determination of the atomic displacements in NbC 0.72

Integrated X‐ray intensities of Bragg peaks have been measured with an NbC 0.72 single‐crystal which contains a large number of non‐stoichiometric carbon vacancies. By standard structural analysis the mean‐square displacements were determined to be ( u 2 Nb ) = 0.0041 (7) Å 2 for Nb atoms and ( u 2 C ) = 0.0111 (20) Å 2 for C atoms. This ( u 2 Nb ) is comparable to the value of 0.0045 Å 2 , extrapolated from the compositional dependence of ( u 2 Nb ) proposed by Metzger, Peisl & Kaufmann [ J. Phys. F. (1983). 13 , 1103–1113]. It was confirmed that the existence of carbon vacancies induces larger static displacements of neighbouring niobium atoms, and the contribution of thermal displacements to the observed ( u 2 Nb ) appears to be rather small in a non‐stoichiometric niobium monocarbide.