Origin of the large thermoelectric power in oxygen-variable RBaCo_{2}O_{5+x} (R=Gd, Nd)

TL;DR

This study investigates the thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single crystals, revealing that charge carrier entropy and hopping transport contribute to their large thermoelectric power.

Contribution

It demonstrates that configurational entropy and spin/orbital degeneracy significantly influence the thermoelectric response in oxygen-variable cobalt oxides.

Findings

Hopping transport character in thermoelectric response

Divergence of Seebeck coefficient at x=0.5

Charge carrier entropy as a key factor

Abstract

Thermoelectric properties of GdBaCo_{2}O_{5+x} and NdBaCo_{2}O_{5+x} single crystals have been studied upon continuous doping of CoO_2 planes with either electrons or holes. The thermoelectric response and the resistivity behavior reveal a hopping character of the transport in both compounds, providing the basis for understanding the recently found remarkable divergence of the Seebeck coefficient at x=0.5. The doping dependence of the thermoelectric power evinces that the configurational entropy of charge carriers, enhanced by their spin and orbital degeneracy, plays a key role in the origin of the large thermoelectric response in these correlated oxides.