Die niederen Oxide des Niobs

Abstract

The lower oxides of niobium can be divided into four groups: 1. (i) NbO x , NbO y , and NbO z ; 2. (2) NbO and NbO 2; 3. (3) homologous series of oxides Nb 3n+1 O 8n−2 with n = 6, 7, and 8, these are NbO 2.42, NbO 2.46, and NbO 2.48; and 4. (4) some lower niobium oxides not yet thoroughly investigated. NbO x , NbO y , and NbO z form only by oxidation of niobium, or by ageing of niobium that is supersaturated with oxygen in definite ranges of temperature and oxygen pressure. NbO and NbO 2 can be made by oxidation of niobium or by reduction of Nb 2O 5. They are stable upto the melting point and are also present in the vapour phase. NbO 2.42, NbO 2.46, and NbO 2.48 form within alloys of appropriate composition by long time tempering at ~ 1100°C. Probably they are not stable up to the melting point. NbO x : (Nb 6O) forms at 300–500°C. According to X-ray diffraction it is tetragonal with a = 3.39 A ̊ , c a = 0.97 . According to electron diffraction of thin, singlecrystal films in transmission, NbO x has a superstructure with a = 4a Nb = 13.5 A ̊ , c a = 0.97 . NbO x is isomorphous with TaO x (Ta 6O). NbO y forms at 350–500°C. According to X-ray studies NbO y (part (a)) is orthorhombic and isomorphous with TaO y (Ta 4O) ; according to electron diffraction of monocrystalline thin films it is cubic with a = 2a Nb = 6.9 A ̊ . NbO y (part (b)), formula Nb 4O, is according to X-ray and electron diffraction tetragonal with a = 2a Nb = 6.65 A ̊ , c a = 0.5 . NbO z forms at 400–700°C. It is tetragonal with a = 6.645 A ̊ , c a = 0.72 . It is isomorphous with TaO z (Ta 2O).