Establishment of strongly overdoped states in the HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+{delta}} superconductor
- Materials and Structures Laboratory, and Department of Innovative and Engineered Materials, Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology, Yokohama 226 (Japan)
- Materials and Structures Laboratory, Tokyo Institute of Technology, Yokohama 226 (Japan)
- Hokkaido Electric Power Co., Ebetsu, Hokkaido 067 (Japan)
Strongly overdoped HgBa{sub 2}Ca{sub 2}Cu{sub 3}O{sub 8+{delta}} (Hg-1223) samples with superconducting transitions as low as 97 K were successfully obtained by using HgO, Ca{sub 2}CuO{sub 3}, CuO, and mixtures of highly oxidized BaCuO{sub 2+{epsilon}} ({epsilon}{approx}0.13) and/or BaO{sub 2} powders as starting materials for the high-pressure synthesis at 5 GPa and 950{degree}C. The overdoped state was confirmed by observing negative values for the Seebeck coefficient throughout the temperature range from T{sub c} to 320 K in a thermoelectric power measurement. Also, both of the cell parameters a and c were found to decrease with decreasing T{sub c}, reflecting, respectively, an increase in hole concentration in the CuO{sub 2} planes and the incorporation of oxygen into the HgO{sub {delta}} layer. The oxygen excess {delta} as determined by the Cu(+I)/Cu(+II) coulometric titration method, was {approximately}0.19 in the overdoped sample with T{sub c}=107K. Subsequent reducing annealing in an Ar atmosphere at 280{degree}C increased the T{sub c} to 131 K. Consistently, only positive Seebeck coefficient values were observed up to 320 K for the Ar-annealed sample. A clearly underdoped material with T{sub c}=118K was obtained by annealing the same sample in Ar at a higher temperature ({approximately}400{degree}C). Finally, high-pressure synthesis starting from less-oxidized BaCuO{sub 2+{epsilon}} ({epsilon}{approx}0.06) yielded a Hg-1223 material with {delta}{approx}0.10 and T{sub c}=132K. {copyright} {ital 1997} {ital The American Physical Society}
- OSTI ID:
- 550552
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 56, Issue 22; Other Information: PBD: Dec 1997
- Country of Publication:
- United States
- Language:
- English
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