H 99 Hydrogen in nonstoichiometric cubic niobium carbides: Neutron vibrationalspectroscopy and neutron diffraction studies / A. V. Skripov, H. Wu, T. J. Udovic, Q. Huang, R. Hempelmann, A. V. Soloninin, A. A. Rempel, A. I. Gusev // Journal of Alloys and Compounds. - 2009. - Vol. 478. - P68-74 : il. - Bibliogr. : p. 73-74 (26 ref.) Рубрики: ХИМИЧЕСКИЕ НАУКИ Кл.слова (ненормированные): СТРУКТУРА КРИСТАЛЛИЧЕСКАЯ -- НЕСТЕХИОМЕТРИЯ -- КАРБИД НИОБИЯ Аннотация: The vibrational spectra and positions of H(D) atoms in NbC1.yHx(Dx) (0.19.y.0.29, 0.04.x.0.30) have??been studied by inelastic neutron scattering (INS) and neutron diffraction. The analysis of the neutron??diffraction data forNbC0.76Hx(Dx) andNbC0.71Hx(Dx) has revealedanumber of different structures depending on the carbon concentration and the presence of absorbed H(D) atoms: the partially ordered cubic??Pmmm structure for NbC0.76, the partially ordered orthorhombic Pmmm structure for NbC0.76D0.17 and NbC0.76H0.18, the disordered cubic FmЃP3mstructure for NbC0.71 and NbC0.71D0.30, and the disordered tetragonal I4/mmm structure for NbC0.71H0.28. The INS spectra of NbC0.81Hx and NbC0.76Hx(Dx) in the energy transfer range 40.140meV are found to consist of a single fundamental peak due to hydrogen optical??vibrations (centered at 98meV for H and at 65meV for D) and a single peak due to carbon optical vibrations (centered at 78 meV). In addition to these peaks, the INS spectrum of NbC0.71H0.28 exhibits a peak at 130 meV, suggesting that H atoms in this compound occupy the sites displaced from the centers of carbon vacancies |