Establishment of strongly overdoped states in the HgBa2Ca2Cu3O8+[delta] superconductor

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Volume Title
School of Chemical Technology | A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Date
1997
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Mcode
Degree programme
Language
en
Pages
14790-14796
Series
Physical Review B, Volume 56, Issue 22
Abstract
Strongly overdoped HgBa2Ca2Cu3O8+δ (Hg-1223) samples with superconducting transitions as low as 97 K were successfully obtained by using HgO, Ca2CuO3, CuO, and mixtures of highly oxidized BaCuO2+ε (ε≈0.13) and/or BaO2 powders as starting materials for the high-pressure synthesis at 5 GPa and 950 °C. The overdoped state was confirmed by observing negative values for the Seebeck coefficient throughout the temperature range from Tc to 320 K in a thermoelectric power measurement. Also, both of the cell parameters a and c were found to decrease with decreasing Tc, reflecting, respectively, an increase in hole concentration in the CuO2 planes and the incorporation of oxygen into the HgOδ layer. The oxygen excess δ as determined by the Cu(+I)/Cu(+II) coulometric titration method, was ∼0.19 in the overdoped sample with Tc=107K. Subsequent reducing annealing in an Ar atmosphere at 280 °C increased the Tc 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 Tc=118K was obtained by annealing the same sample in Ar at a higher temperature (∼400°C). Finally, high-pressure synthesis starting from less-oxidized BaCuO2+ε (ε≈0.06) yielded a Hg-1223 material with δ≈0.10 and Tc=132K.
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Keywords
superconductors, transitions
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Citation
Fujinami, K. & Ito, T. & Suematsu, H. & Matsuura, K. & Karppinen, Maarit & Yamauchi, H. 1997. Establishment of strongly overdoped states in the HgBa2Ca2Cu3O8+[delta] superconductor. Physical Review B. Volume 56, Issue 22. 14790-14796. ISSN 1550-235X (electronic). DOI: 10.1103/physrevb.56.14790.