Abstract
We report temperature dependences of the electrical resistivity and photoemission spectra of (La 1− x Ca x O)Cu 1− x Ni x S which is derived by the substitution of Ca and Ni for La and Cu, respectively, in a wide-gap semiconductor (LaO)CuS with a layered structure. The temperature dependence of the electrical resistivity changes from semiconducting to metallic with the concentration x successively. The appearance of new density of states in the vicinity of Fermi energy is observed in the photoemission spectra. In the sample of x=0.03, a semiconductor–metal transition occurs at 150 K with no specific heat anomaly. A resistivity increase proportional to ln T and a positive magneto-resistance are observed for x=0.03∼0.06 at low temperature.
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