Single Layer In-O Atomic Sheets as Phonon and Electron and Barriers in ZnO-In2O3 Natural Superlattices: Implications for Thermoelectricity

TL;DR

This study investigates natural superlattices in ZnO-In2O3 systems, revealing that InO2 sheets act as phonon scatterers and electron barriers, impacting thermoelectric properties through atomic structure and potential barriers.

Contribution

It introduces atomic-scale insights into InO2 sheets in ZnO-In2O3 superlattices and their dual role in phonon scattering and electron transport barriers, advancing thermoelectric material understanding.

Findings

InO2 sheets decrease thermal conductivity via phonon scattering.

InO2 sheets create potential barriers affecting electron transport.

Superlattice spacing influences barrier properties and thermoelectric performance.

Abstract

The phases in the ZnO half of the ZnO-In2O3 binary system are natural superlattices consisting of periodic stacking of single InO2 sheets separated by indium doped ZnO blocks with a spacing that depends on the composition according to the relationship In2O3(ZnO)k. Characterization by combined, atomic resolution, aberration-corrected scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) analysis, indicates that the atomic structure of each InO2 layer consists of a single continuous sheet of octahedrally-coordinated InO2. The sheets also are crystallographic inversion boundaries. Analysis of the electrical conductivity, thermal conductivity and Seebeck coefficient data at 800 oC indicates that the InO2 sheets not only decrease thermal conductivity by phonon scattering but also create potential barriers to electron transport. The origin of the potential barriers, the role of piezoelectric effects and their dependence on superlattice spacing is discussed qualitatively. It is also argued that the crystallographically-aligned InO2 sheets within individual grains are also transport barriers in randomly oriented polycrystalline materials.