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Coexistent Phases and their Electrical and Structural Behaviour in the Ternary Re/Mo/O System
Author(s) -
Doerr M.,
Feller J.,
Oppermann H.
Publication year - 1996
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/crat.2170310219
Subject(s) - solid solution , electron microprobe , ternary operation , crystallography , solubility , chemistry , diffraction , analytical chemistry (journal) , phase diagram , electrical resistivity and conductivity , x ray crystallography , metal , phase (matter) , lattice constant , homogeneous , mineralogy , thermodynamics , physics , quantum mechanics , organic chemistry , chromatography , computer science , optics , programming language
In order to complete and improve phase diagrams of transition metal oxides the existence and properties of compounds in the Re/Mo/O system have been investigated. Single crystalline solid solutions Re 1‐ x Mo x O 2 (0 < x < 0.37) and Mo 1‐ y Re y O 2 (0 < y < 0.42) were prepared by Solid State Reactions and Chemical Transport Reactions (CTR) and characterized by means of X‐ray‐diffraction, ICP‐AES, and EPMA. In addition, it was shown that the trioxides Re 1‐ x Mo x O 3 or Mo 1‐ y Re y O 3 respectively, do not prove a distinct solubility. First results on Re‐doped Magneli phases of Mo are also discussed. There were found two series of solid solutions Mo 4‐ z Re z O 11 (0 < z < 0.40) which derive from γ‐Mo 4 O 11 and η‐Mo 4 O 11 . The other Magneli phases did not show a significant Re content. Using X‐ray diffraction, AFM and optical microscopy the structure and morphology of single crystals has been studied. It was steated that the dioxide solid solutions were very homogeneous and structural phase transitions depending on x or y did not occur. That is in good agreement with measurements of electrical conductivity σ in the temperature range from 20 K to 300 K in which the samples showed the behaviour of metals with lattice defects. The Magneli phases Mo 8 O 23 and Mo 9 O 26 turned out to be “narrow gap semiconductors” in the low temperature range with activation energies of less than 0.1 eV. The γ‐Mo 4 O 11‐ and γ‐Mo 4 O 11 crystals, the pure and Re‐doped ones, were found as metallic conductors at higher temperatures and below a transition temperature they show a semiconductive behaviour.