Effects of Mn and/or Ni substitutions for Fe on thermoelectric properties of magnetite prepared by sintering

Effects of Mn and/or Ni substitutions for Fe were investigated on thermoelectric properties in sintered magnetite (Fe₃O₄) for temperature range 200-700°C. Substitutions were performed in 4 series; (1) Mn_xFe_3-xO₄ (0≤x≤ 0.8), (2) Ni_xFe_3-xO₄ (0≤x≤ 0.8), (3) (Mn₁2/Ni₁2/)_xFe_3-xO₄ (0≤ x≤1.2) and (4) (Mn₂3/Ni₁3/)_xFe_3-xO₄ (0≤ x≤ 1.2). The values of electrical resistivity (ρ) and Seebeck coefficient (S) for series (1) and (2) were found to be similar to the previously reported results for magnetite single crystal. Common to the 4 series, ρ slightly decreased with temperature, and S and thermoelectric power factor S²/ρ increased with temperature. For series (4) with x=0.4, there was a case the thermoelectric power factor exceeded that of magnetite.