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曹光旱, Guanghan
PHYSICAL REVIEW B 69, 045106 (2004),-0001,():
-1年11月30日
The pseudobinary thiospinel system Cu1-xCdxIr2S4 was investigated by the x-ray-diffraction, electrical resistivity, magnetic-susceptibility, and specific-heat measurements. It was shown that the system exhibits a miscibility-gap behavior for the Cd substitution, however, nearly monophasic samples were obtained by quenching at 1373 K, except for 0.4<x≤0.6. With increasing the Cd concentration, the room-temperature electrical conductivity and Pauli susceptibility decrease monotonically, consistent with the hole-filling picture. The first-order metal-insulator transition at about 230 K in the parent compound CuIr2S4 is changed into a second-order transition around 185 K when x~0.25, whereafter the second-order transition disappears at x~0.8. No superconductivity was observed down to 1.8 K. The end-member compound CdIr2S4 is shown as an insulator with a band gap of 0.3 eV. Analysis for the data of magnetic susceptibility and electrical resistivity suggests the formation of bipolarons below 185 K for 0.25<x<0.8, which accounts for the absence of superconductivity in terms of the transition from the BCS Cooper pairs to small bipolarons.
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