Fabrication and Low Temperature Thermoelectric Properties of Na_xCoO_2 (x = 0.68 and 0.75) Epitaxial Films by the Reactive Solid-Phase Epitaxy

TL;DR

This study reports the fabrication of high-quality Na_xCoO_2 epitaxial films with controlled sodium content via reactive solid-phase epitaxy, and investigates their low-temperature thermoelectric properties, revealing large thermoelectric power and quasiparticle behavior.

Contribution

It introduces a novel fabrication method for Na_xCoO_2 thin films with controlled composition and demonstrates their promising thermoelectric properties at low temperatures.

Findings

Epitaxial growth confirmed by x-ray diffraction.

Large thermoelectric power similar to single crystals.

High-quality films with low residual resistivity.

Abstract

We have fabricated Na_xCoO_2 thin films via lateral diffusion of sodium into Co_3O_4 (111) epitaxial films (reactive solid-phase epitaxy: Ref. 4). The environment of thermal diffusion is key to the control of the sodium content in thin films. From the results of x-ray diffraction and in-plane resistivity, the epitaxial growth and the sodium contents of these films were identified. The thermoelectric measurements show a large thermoelectric power similar to that observed in single crystals. The quasiparticle scattering rate is found to approach zero at low temperatures, consistent with the small residual resistivity, indicating high quality of the Na_xCoO_2 thin films.