X-RAY AND NEUTRON-SCATTERING STUDY OF THE NB-O SOLID-SOLUTIONS

Niobium-oxygen solid solutions were studied by x-ray diffraction and i nelastic neutron scattering (INS). Niobium rods (diameter 10 mm, lengt h 80 mm) were doped with oxygen in a high-vacuum induction furnace in an oxygen atmosphere. Laue diffraction showed that the Nb-O samples ha d a ''bamboo'' structure with a single crystal length ranging from 5 m m to 10 mm, powder samples prepared from the rods were used to measure the lattice parameters. The observed increase of the lattice paramete rs due to interstitial oxygen is in agreement with literature data. Th e vibrational frequency distribution of NbO0.026, was measured by a ti me-of-flight neutron spectrometer at room temperature, and at 200 degr ees C to increase the intensity of the energy gain INS in the region o f the oxygen vibrations. In addition to the known vibrational mode of interstitial oxygen at omega(1,2)=45 meV, a high-energy mode at omega( 3)=84.2 meV was observed. This mode corresponds to oxygen vibrations p olarized along the short axes of the octahedral position. (C) 1998 Els evier Science S.A.