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A series of solid solutions between Sr 2 (FeMo)O 6 and Sr 2 (FeW)O 6 were synthesized and their electrical properties were studied by the measurements of both the temperature dependence of the electrical conductivity and the Seebeck coefficient. The valence states of iron ions were studied by the Mössbauer effect measurements. The compounds in the range (0.5≤ x ≤1) have high conductivity (ρ≃10 -3 ohm·cm) with the metallic type. The valence distribution between the B sublattice ions is considered to be Sr 2 (Fe 3+ Mo x 5+ W 1- x 5+ )O 6 . The compounds in the range (0.3≤ x ≤0.4) is considered to be a semiconductor with a very small energy gap or a degenerate semiconductor. And the compound in the range (0≤ x ≤0.2) may be called semiconducting. A mixed valence compound Sr 2 (Fe 1- x 2+ Fe x 3+ Mo x 5+ W 1- x 6+ )O 6 will be formed in the range (0≤ x ≤0.1). The rapid change in valence in the range (0.1≤ x ≤0.4) is evidenced by a rapid replacement of the Fe 3+ ions for the Fe 2+ ions.
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