Indium-Assisted Gallium Solubility Expansion and Defect Hierarchy Evolution in Thermoelectric ZnO Ceramics

Area of Science:

• Materials Science
• Solid State Chemistry
• Nanotechnology

Background:

• Zinc oxide (ZnO) is a promising material for thermoelectric applications.
• Controlling defect chemistry and dopant solubility is crucial for optimizing ZnO's thermoelectric performance.
• Existing methods often result in secondary phases that hinder optimal transport properties.

Purpose of the Study:

• To investigate the role of Indium-Gallium co-doping in ZnO ceramics.
• To elucidate how defect chemistry and dopant solubility influence thermoelectric transport.
• To engineer microstructures for enhanced thermoelectric efficiency.

Main Methods:

• Solid-state reaction synthesis of Ga-In co-doped ZnO ceramics.
• Microstructural and structural analysis (e.g., XRD, SEM).
• Thermoelectric property measurements (e.g., Seebeck coefficient, electrical conductivity, thermal conductivity).

Main Results:

• Indium-Gallium co-doped ZnO (IGZO) exhibited a composite-like microstructure with a minor Ga2O3(ZnO)9 spinel phase.
• Indium incorporation expanded Gallium solubility in the ZnO lattice, suppressing spinel cluster formation.
• Atomic-scale defects became dominant in IGZO, leading to reduced lattice thermal conductivity.
• Enhanced Ga substitution, aided by In, modified the electronic structure, increasing carrier concentration.
• A figure of merit (ZT) of 0.182 at 1073 K was achieved.

Conclusions:

• Solubility-assisted defect engineering is an effective strategy for tuning thermoelectric properties in ZnO.
• Controlling the hierarchy between secondary phases and point defects is key to optimizing phonon scattering.
• Indium-Gallium co-doping offers a pathway to enhanced thermoelectric performance in ZnO-based materials.