非化学量論的TiO相ならびにVO相の欠陥構造

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タイトル別名
  • Defect Structure of Nonstoichiometric TiO and VO Phases
  • ヒカガクリョウロンテキ TiOソウ ナラビニ VOソウ ノ ケッカン コウゾウ

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The measurement of the density and of the lattice parameter was performed over a wide range of composition of TiO and VO phases, and also by the neutron diffraction the position of oxygen ions in their lattices as well as the relative intensity of diffraction lines was determined. From these measurements it has been confirmed that the phases are hormogeneous in the range of TiO0.82-TiO1.23 or VO0.81-VO1.20 and have the NaCl type lattice structure with a large concentration of the vacant lattice sites in both of the metal ion and oxygen ion sublattices. The lattice parameters of these phases are very small in comparison with those of the 3d-transition metal monoxides such as FeO or NiO and are rather close to that of the metallic titanium and vanadium. It is predicted that the existence of such a large amount of vacancies which account for about 15∼20% of the lattice point produce a sort of metallic bonding through overlapping the 3d-orbitals by the reduction of lattice parameter, thus leading the crystal to a state of lower internal energy. Therefore, to attain the state of the lower energy, the occurrence of a large amount of the Schottky pair of vacancies is required in addition to the lattice vacancies whose concentration corresponds to the deviation from the stoichiometric composition. The gain in the internal energy of crystal due to the Schottky pair defect was calculated as a function of the composition and the relations between the vacancy concentration and composition were deduced in good agreement with the observed values for TiO and VO phases. The energy gain due to the formation of the Schottky pair defect was estimated to be about −1 eV at the stoichiometric composition and the estimated fraction of the pair of vacancy produced by thermal agitation was less than 1% even at a high temperature near 2000°K. These results explain the fact that the observed values of the vacancy concentration under various conditions of heat treatment are in agreement within 1%.

収録刊行物

  • 日本金属学会誌

    日本金属学会誌 31 (5), 611-617, 1967

    公益社団法人 日本金属学会

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