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曹光旱, Guanghan
J. Phys. D: Appl. Phys. 40 (2007) 2899-2905,-0001,():
-1年11月30日
CaCu3Ti4O12
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曹光旱, Zhi
J. Phys.: Condens. Matter 18 (2006) L379-L384,-0001,():
-1年11月30日
We report the measurements of thermopower, electrical resistivity and thermal conductivity in a complex cobalt oxide Li0.48Na0.35CoO2, whose crystal structure can be viewed as an intergrowth of the O3 phase of LixCoO2 and the P2 phase of NayCoO2 along the c-axis. The compound shows a large roomtemperature thermopower of ∼180 μV K−1, which is substantially higher than those of LixCoO2 and NayCoO2. The figure of merit for the polycrystalline sample increases rapidly with increasing temperature, and achieves nearly 10−4 K−1 at 300 K, suggesting that the LixNayCoO2 system is a promising candidate for thermoelectric applications.
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曹光旱, Guanghan
PHYSICAL REVIEW B, VOLUME 64, 214514,-0001,():
-1年11月30日
The thiospinel system Cu1-xZnxIr2S4 (0≤x≤0.9) has been studied by x-ray diffraction, electrical resistivity, and magnetic susceptibility measurements. The parent compound CuIr2S4, being metallic at room temperature, undergoes a structural phase transition towards lower symmetry around 230 K and becomes an insulator at the low temperature. The Zn substitution for Cu was found to drastically suppress the metal-to-insulator (MI) transition, resulting in the appearance of superconductivity. The MI transition temperature TMI and the extent of the structural distortion both decrease with increasing x until the phase transition is completely suppressed at x~0.4. In the region of x≤0.4, the cubic spinel phase coexists with the low-symmetry phase below TMI. For the metallic phase, the change of the Pauli paramagnetic susceptibility indicates the hole-filling mechanism due to an excess electron from the Zn substitution for Cu. The insulating state of the low-symmetry phase is tentatively explained in terms of charge ordering combined with the Ir4+ dimerization. Bulk type-II superconductivity below 3.4 K is observed for 0.25≤x≤0.8 samples. The superconducting transition temperature decreases with increasing the Zn content. The abnormal behavior of the normal-state resistivity below 200 K for 0.3≤x≤0.5 samples suggests modification of the electronic states, which might be related to the occurrence of superconductivity.
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