Effect of 4d Transition Metal Atom Rh Doping on Thermoelectric Power, Magnetic Susceptibility, Thermal Expansion and X-Ray Photoemission Spectra in the Charge-Transfer Type Nonmetallic State of NiS

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We report the following two remarks of the Rh impurity effect on the charge-transfer (CT) type nonmetallic state (below the nonmetal-metal transition temperature : T_t) of 3d transition metal compound NiS. (1) Although the nearest neighbouring M-M (Ni or Rh) and S-S distances increase with increasing x, dT_t/dx<0. The Rh substitution gives a broad peak with the Fermi edge. A positive sign of T-linear contribution of the thermoelectric power turns to negative one at the critical concentration (x_c) in Ni_<1-x>Rh_xS. Below T_t, a Curie constant is observed and increases with increasing x. It is suggested that an impurity band introduced by the Rh atoms leads a change of the electronic state of Ni atoms and the suppression of the CT gap. (2) An empirical relation (dT_t/d |C_N|>0) is found on Ni_<1-x>Rh_xS, Ni_<1-δ>S and NiS_<1-y>Se_y, where C_N is the phonon-drag coefficient. The slope dT_t/d |C_N| becomes smaller in Ni_<1-x>M_xS with the early 3d transition metal impurities (M : Ti, V and Cr).
社団法人日本物理学会の論文
1995-07-15