Transport properties and electronic states of the thermoelectric oxide NaCo_2O_4

TL;DR

This paper reviews the physical properties of NaCo_2O_4, highlighting its high thermoelectric efficiency due to enhanced effective mass and entropy effects, and discusses a spin-density-wave transition induced by Cu substitution.

Contribution

It provides a concise overview of the thermoelectric properties and electronic states of NaCo_2O_4, emphasizing the role of entropy and spin states in its behavior.

Findings

High thermoelectric properties linked to enhanced effective mass

Spin-density-wave transition at 22 K with Cu substitution

Large entropy confined in CoO_2 block influences electronic states

Abstract

Physical properties of the thermoelectric oxide NaCo_2O_4 are briefly reviewed. The high thermoelectric properties of this material are attributed to the substantially enhanced effective mass, which comes from the large entropy of Co$^{4+}$ in the low spin state. The large entropy confined in the CoO_2 block causes a spin-density-wave transition at 22 K upon Cu substitution for Co, which can be regarded as ``order from disorder''.