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) Fe_3-xMn_xO₄(0≤x≤1.2), (2) Fe_3-yNi_yO₄(0≤y≤1.2), (3) Fe_3-x-yMn_xNi_yO₄(0≤x+y≤1.2) with x=y and (4) Fe_3-x-yMn_xNi_yO₄(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.