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- 저자 : Nawazish Ali Khan (검색결과 2 건)
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Dielectric Properties of Cu0.5 Tl0.5 Ba Ca3 Cu4−y Zny O12−δ (y = 0, 3) Superconductors
Adnan Younis,Nawazish Ali Khan,Naeem Ullah Bajwa 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.57 No.6
The dielectric properties of Cu0.5 Tl0.5 Ba Ca3 Cu4−y Zny O12−δ (y = 0, 3) superconductors have been studied to investigate the doping effects of Zn atoms in Cu0.5 Tl0.5 Ba Ca3 Cu4−y Zny O12−δ(y = 0, 3) superconductors. The role of doping in modifying the dielectric properties, such as the dielectric loss (tan δ) and the ac-conductivity (σac) by means of capacitance (C) and conductance (G) measurements has been studied at test frequencies (f) in the range of 10 to 10 MHz. These dielectric properties have been investigated in the normal state of the samples at room temperature and in their superconducting state. From these analyses, we determine the excess conductivity in the superconducting state (lower energy state) of the system and suggest its possible role in the mechanism of superconductivity. A negative capacitance (NC) phenomenon has been observed in the dielectric measurements of these samples, which most likely arises due to difference in the Fermi levels of the contact electrodes with the superconductor ceramic sample. Due to higher Fermi levels of the ceramics, there is a flow of the carriers from the ceramic sample towards the metal electrodes. A comparison of the dielectric properties of previously reported Tl2 Ba2 Ca2 Cu2 Ox samples to those of Cu0.5 Tl0.5 Ba Ca3 Cu4−y Zny O12−δ(y = 0, 3) samples has shown that our samples display lower losses and higher ac conductivities at 300 K and 80 K. This difference most likely arises due to a difference in the thicknesses of the charge reservoir layers of these materials. The decreased dielectric loss in our Zn-doped samples strongly suggests that the polarization most likely arises due to the separation of charges between the Cu0.5 Tl0.5 Ba2 O4−δ charge reservoir layer and mobile carriers in the conducting CuO2 /ZnO2 planes because the charge reservoir layer has localized charges at Ba+2, Tl+3, Cu+2 site, whereas CuO2/ZnO2 planes contain mobile charge carriers displaced from their equilibrium position by the external applied frequency.
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