Thermoelectric power and superconducting properties of Y_{1}Ba_{2}Cu_{3}O_{7-δ} and R_{1}Ba_{2}Cu_{3}O_{7-δ}

Abstract

The high-${T}_{c}$ superconductors ${R}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ (R denotes rare-earth elements) and ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ are prepared in several different processes. ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ prepared in flowing ${\mathrm{O}}_{2}$ and slowly cooled shows ${T}_{c}$=94 K, a lattice parameter ratio c/b=3.00 and negative thermoelectric power S, while quench-cooled ${\mathrm{Y}}_{1}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ shows reduced ${T}_{c}$, an elongated structure along the c axis with c/b=3.02, and positive S. Most of the rare-earth-element superconductors show ${T}_{c}$ near or higher than 90 K. Rare-earth-element superconductors with the rare-earth-element ionic radius larger than 0.92 A\r{} show positive S, while those with the ionic radius smaller than 0.92 A\r{} show negative S. These experimental results seem to indicate a close correlation between the structural strain and the superconducting properties.