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 118K. 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 (=118K) 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phase, both Cu L-edge and O K-edge XANES results suggest that some portion of charge-reservoir copper atoms may have been replaced by CO, i.e., (Cu1-xCx)Ba 2Ca2Cu3O8+x+z. The variation range of excess oxygen was estimated at Δz≈0.3.
- Cu-1223 high-T superconductor
- Hole concentration
- Oxygen content
- Wet-chemical analysis
- XANES spectroscopy