X-ray diffraction study of Debye temperature and charge distribution in tantalum monocarbide

Intensities of Bragg reflexions from powder samples TaCsub(0.99) and TaCsub(0.81) are measured in the temperature range from 22 to 940 0C. The values of Debye temperature thetasub(M) corresponding to 22 0C are (475+-4) and (440+-3) K, for the two respective compositions, indicating thus the decrease of thetasub(M) with increasing deficiency of carbon atoms in the structure. The measured temperature dependence of thetasub(M) can be described by a quasiharmonic approximation of the thermal vibration of atoms. The electron distributions of the atoms are analysed in terms of deviations of the measured scattering factors from the theoretical ones, calculated for the free atoms in the directions [hhh], [hh0], and [h00]. It is found that, in comparison with the free-atom model, the charge density of tantalum atom is extended radially and the carbon atom is contracted. (author)