Effects of Mn and/or Ni substitutions for Fe on thermoelectricroperties of magnetite prepared by sintering
Y. Nakada1, N.Koseki1, A. Sato1, Y. Oikawa1, H. Ozaki1,K. Inoue2, Y. Beppu2, Y. Nakano3,
A. Usami3, K.Tanaka3
1Department of ElectricalEngineering and Bioscience, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku,Tokyo, 169-8555 Japan
2Research laboratory, KyusyuElectric Power Co., Inc., Fukuoka, 815-8520 Japan
3Central Research Institute ofElectric Power Industry, Komae, Tokyo, 201-8511 Japan
Effects of Mn and/or Nisubstitutions for Fe on thermoelectric properties of sintered magnetite (Fe3O4)were investigated for temperature region 100 oC–800 oC. Substitutions were performed in 4 kindsof series; (1) Fe3-xMnxO4(0≤x≤1.2), (2) Fe3-yNiyO4(0≤y≤1.2), (3) Fe3-x-yMnxNiyO4(0≤x+y≤1.2) with x=y and (4) Fe3-x-yMnxNiyO4(0≤x+y≤1.2) with x=2y (equivalence with Fe). XRD and XPS measurements confirmed thatthe substitutions were made uniformly and samples were single phase of spinelstructure. The Seebeck coefficient S showed negative values for the wholemeasurements and the Sof magnetite (x=y=0) showed similar value to that previously reported forsingle crystal. There was not a remarkable difference in the substitutioneffect on Sbetween Mn, Ni and Mn+Ni substitutions with equal total substitution content.
It was found that the absolutevalue of Seebeck coefficient |S| increased with increasing the substitutions of Mn, Ni andMn+Ni. |S|increased monotonically with increasing temperature for all samples and itexceeded 200 mV/K at800 oC for x+y=0.8. The electrical resistivity remainedin the same order of magnitude in these substitutions as those for magnetite.