The dynamics of O atoms in Ta-O solid solution were studied by using the slow-neutron inelastic scattering method. Evidence was obtained for the existence of vibration-rotation excitations of an interstitial atom in a metal lattice. In addition to the peaks corresponding to the fundamental oscillations of a harmonic oscillator (ω1,2 ≈ 0.042eV and ω3 ≈ 0.082eV), side-bands with an energy of about ω3 ± 0.006eV were observed in the atomic O spectrum. Analysis of the spectral structure led to the assumption that the observed satellites were attributed to vibration-rotation excitations of an impurity O atom in the field of the metal atoms surrounding it. The O atom was thought to be displaced in the basal plane from the center of the octahedral interstice of the crystal lattice and was able to move freely along a slightly corrugated energy channel around the geometrical center of the octahedron. The energy positions of the side-bands were in good agreement with the excitation energies estimated from the model by superposing 2 circular motions of the O atom in the basal plane of the Ta lattice near to the center of the octahedral interstice.

Side Bands of the Vibrational Spectrum of Interstitial Elements in a Metal Lattice. S.I.Morozov, V.V.Kazarnikov, A.S.Ivanov: JETP Letters, 2006, 83[11], 497-500