Thermal Expansion Thermoelectric Power,and XPS Study of the Nonmetal-Metal Transition in Ni_<1-x>S_<1-y>Se_y

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Magnetic susceptibility z, electrical resistivity p, thermoelectric power S, XPS spec-tra and hexagonal lattice parameters c and a are measured on the NiAs-type Ni. .S. ,Se, (,v?0.04; y@ 1.00). We find the followings (1) the nonmetal-metal transitiontemperature T., the phonon-drag coefficient C below T. and d 7 (T >T.) / d T decreaseand they are suppressed at x. and y. with increase in x and y, respectively. (2) Thenearest neighboring S. ,Se,(Z)-Z, Ni-Z and Ni-Ni distances just below T. (D,NNNN4D., , 7[).?-.?, respectively) are depressed wuth uncrease in x. D,-. and D., ., only slught-NIy depend on y, while D., , uncreases with increasing y. (3) No change in the d'L peak(L: hole in the Z network) in the valence band region is observed among Ni. ,S. ,Se,and Ni..,.Te. (4) The Ni 2?d'L core level peak shifts to lower binding energy E.with increasing y, while it hardly changes with x. (5) The E. of S 2s and S 2p corelevels decrease with increasing x ; the E. of S 2 p one decreases with increasing y. Fromthe view point of the charge-transfer model, the pressure and the Ni-vacancy substitu-lion effects on T. are mainly explained by the increase in the Z ( p) band width, and theSe-substitution effect by the decrease in the charge-transfer energy. The Ni-vacanciesalso introduce extra holes in the 'l.(p) band.nonmetal-metal transition, charge transfer, XPS, thermal expansion, ther-moelectric power, magnetic susceptibility, electrical resistivity, Ni. ..S. ,Se,
社団法人日本物理学会の論文
1991-12-15

Thermal Expansion Thermoelectric Power,and XPS Study of the Nonmetal-Metal Transition in Ni_<1-x>S_<1-y>Se_y

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