Thermal conductivity of the thermoelectric layered cobalt oxides measured by the Harman method

TL;DR

This study measures the in-plane thermal conductivity of layered cobalt oxides using the Harman method, revealing the dominant role of the charge reservoir block and slight anisotropy due to misfit structure, informing thermoelectric material design.

Contribution

It introduces the use of the Harman method for measuring in-plane thermal conductivity in layered cobalt oxides and highlights the dominant thermal conduction role of the charge reservoir block.

Findings

Charge reservoir block dominates thermal conduction.

Small in-plane anisotropy observed between a and b axes.

Nano-block integration concept aids in material design.

Abstract

In-plane thermal conductivity of the thermoelectric layered cobalt oxides has been measured using the Harman method, in which thermal conductivity is obtained from temperature gradient induced by applied current. We have found that the charge reservoir block (the block other than the CoO$_2$ block) dominates the thermal conduction, where a nano-block integration concept is effective for material design. We have further found that the thermal conductivity shows a small but finite in-plane anisotropy between $a$ and $b$ axes, which can be ascribed to the misfit structure.