# Systematics in the thermopower behaviour of several series of bismuth and thallium cuprate superconductors: An interpretation of the temperature variation and the sign of the thermopower

Rao, CNR and Ramakrishnan, TV and Kumar, N (1990) Systematics in the thermopower behaviour of several series of bismuth and thallium cuprate superconductors: An interpretation of the temperature variation and the sign of the thermopower. In: Physica C: Superconductivity, 165 (2). pp. 183-188.

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Official URL: http://dx.doi.org/10.1016/0921-4534(90)90166-C

## Abstract

The thermopower, $\alpha$, of many members of the $Bi_2Ca_{1-x}Y_xSr_2Cu_2O_{8+\delta}$, $Bi_{2-y}Pb_yCaSr_2Cu_2O_{8+\delta}$, $Tl_yCa_{1-x}Y_xBa_2Cu_2O_{6+\delta}$ $TlCa_{1-x}Ln_xSr_2Cu_2O_{6+\delta}$ and $TlSr_{2-x}La_xCuO_{5+\delta}$ systems is positive down to $T_c$, but is negative in some of them. The slope of the $\alpha-T$ plots above $T_c$ is generally negative independent of the sign of $\alpha$. The value of $\alpha$ extrapolated to 0 K, $\alpha(0)$, from the high-tem perature regime is finite and generally, positive. Compared to the behaviour of $YBa_2Cu_3O_7$, the data on the $Bi$ and $Tl$ cuprate systems examined here seem to suggest that electrons may be involved in the conduction process as well, at least in systems where both the $\alpha$ and the $\alpha-T$ slope are negative. Of the different systems examined here, $Tl_{1-x}Pb_xCaSr_2Cu_2O_{6+\delta}$ containing $Pb$ in the 4+state, deserves special mention since it shows negative $\alpha$ over the entire temperature range in addition to a negative slope suggesting that this is likely to be a genuine high-$T_c$ electron-superconductor. The thermopower of cuprates has been discussed in some detail in terms of entropic and quasiparticle contributions.

Item Type: Journal Article Copyright of this article belongs Elsevier Science. Division of Chemical Sciences > Solid State & Structural Chemistry UnitDivision of Physical & Mathematical Sciences > Physics Ramya Krishna 22 Aug 2008 30 Jan 2012 05:34 http://eprints.iisc.ac.in/id/eprint/11572