Hole concentration in the three-CuO2-plane copper-oxide superconductor Cu-1223 |
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Authors: | M Karppinen H Yamauchi M Kitabatake R.S Liu J.M Chen |
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Affiliation: | a Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama 226-8503, Japanb Department of Chemistry, National Taiwan University, Taipei, Taiwan, ROCc National Synchrotron Radiation Research Center, Hsinchu, Taiwan, ROC |
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Abstract: | Strongly overdoped samples of the three-CuO2-plane copper-oxide superconductor, CuBa2Ca2Cu3O8+z or Cu-1223, were obtained through high-pressure synthesis and post-annealed to various hole-doping levels so as to have the value of Tc range from 65 to 118 K. A concomitant decrease in the average valence of copper from ∼2.20 to ∼2.05 was evidenced by means of wet-chemical and thermogravimetric analyses and Cu L-edge X-ray absorption near-edge structure (XANES) spectroscopy. The valence value as low as ∼2.05 that corresponds to the highest Tc (=118 K) may be understood by taking into account multiple ways for holes to be distributed among the different Cu-O layers. In terms of actual chemical composition of the Cu-1223 phase, both Cu L-edge and O K-edge XANES results suggest that some portion of charge-reservoir copper atoms may have been replaced by CO, i.e., (Cu1−xCx)Ba2Ca2Cu3O8+x+z. The variation range of excess oxygen was estimated at Δz≈0.3. |
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Keywords: | Cu-1223 high-Tc superconductor Oxygen content Hole concentration Wet-chemical analysis Thermogravimetry XANES spectroscopy |
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