Electrical Properties of Ni1-xS

Abstract

Hexagonal nickel sulfide NiS shows a metal-nonmetal transition with the appearance of antiferromagnetism as temperature is lowered below 265 K ( T t ). Measurements of conductivity, Hall coefficient, thermoelectric power and magnetoresistance were made on polycrystalline samples of hexagonal Ni 1- x S (0.004≦ x ≦0.050). The low temperature phase is found to be a degenerate semiconductor with a high hole density from 3.13×10 20 cm -3 ( x =0.004) to 1.60 ×10 21 cm -3 ( x =0.020), which is essentially due to ionized nickel vacancies. Carriers are mainly scattered by ionized and neutral impurities associated with nickel vacancies. The effective mass is estimated from Seebeck coefficients to have a value between 1.50 m 0 and 2.90 m 0 . Above T t , the compound is a normal metal without a magnetic moment. The low temperature resistivity has revealed the Debye temperature to be 175 K for the metallic phase. There is no apparent evidence of a strong correlation effect although the electronic state densities are l...