Thermoelectric power of Y1-xCaxBa2Cu3O7- delta : Contributions from CuO2 planes and CuO chains.

Abstract

The thermoelectric power (TEP) has been studied for polycrystalline (Y,Yb${)}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ca}}_{\mathit{x}}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7\mathrm{\ensuremath{-}}\mathrm{\ensuremath{\delta}}}$ with variable Ca and O content. The partial substitution of ${\mathrm{Y}}^{3+}$ by ${\mathrm{Ca}}^{2+}$ introduces additional hole carriers into the ${\mathrm{CuO}}_{2}$ planes and allows the 123 system access far into the overdoped regime. Consequently, the CuO chains can be strongly deoxygenated until they are nonmetallic (and no more contribute to the TEP), while the ${\mathrm{CuO}}_{2}$ planes still are optimally doped (${\mathit{T}}_{\mathit{c}}$=${\mathit{T}}_{\mathit{c},\mathrm{max}}$) or even slightly overdoped. Over a fairly wide range of doping this enables us to study the TEP of the 123 system as it arises solely from the ${\mathrm{CuO}}_{2}$ planes (``plane contribution''). This ``plane contribution'' is in good agreement with the general trend reported for various Bi and Tl compounds [S. D. Obertelli, J. R. Cooper, and J. L. Tallon, Phys. Rev. B 46, 14 928 (1992)]. For samples with almost fully oxygenated CuO chains, assuming independent TEP contributions from ${\mathrm{CuO}}_{2}$ planes and CuO chains, we deduce a ``chain contribution'' which is very similar to the results obtained on untwinned single crystals [J. L. Cohn et al., Phys. Rev. B 45, 13 140 (1992)]. \textcopyright{} 1996 The American Physical Society.