Establishment of strongly overdoped states in the HgBa2Ca2Cu3O8+delta superconductor

Article

关键词: HIGH-PRESSURE SYNTHESIS;    THERMOELECTRIC-POWER;    OXYGEN-CONTENT;    RESISTIVITY MEASUREMENTS;    X-RAY;    HGBA2CACU2O6+DELTA;    PHASE;    HGBA2CUO4+DELTA;    DIFFRACTION;    SYSTEM;   

DOI  :  10.1103/PhysRevB.56.14790

来源: SCIE

【 摘 要 】

Strongly overdoped HgBa2Ca2Cu3O8+delta(Hg-1223) samples with superconducting transitions as low as 97 K were successfully obtained bq; using HgO, Ca2CuO3, CuO, and mixtures oi highly oxidized BaCuO2+epsilon (epsilon approximate to 0.13) and/or BaO2 powders as starting materials for the high-pressure synthesis at 5 GPa and 950 degrees C, The overdoped state was confirmed by observing negative values for the Seebeck coefficient throughout the temperature range from T-c, ro 320 K in a thermoelectric power measurement. Also, both of the cell parameters a and c were found to decrease with decreasing T-c reflecting, respectively, an increase in hole concentration in the CuO2 planes and the incorporation of oxygen into the HgOdelta layer. The oxygen excess Sas determined by the Cu(+I)/Cu(+II) coulometric titration method, was similar to 0.19 in the overdoped sample with T-c=107 K. Subsequent reducing annealing in an Ar atmosphere at 280 degrees C increased the T-c to 131 K. Consistently, only positive Seebeck coefficient values were observed up to 320 K fur the Ar-annealed sample. A cli-ally underdoped material with T-c=118 K was obtained by annealing the same sample in Ar at a higher temperature (similar to 400 degrees C). Finally, high-pressare synthesis starting from less-oxidized BaCuO2+epsilon (epsilon approximate to 0.06) yielded a Hg-1223 material with delta approximate to 0.10 and T-c=132 K.

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