Creating Continuously Graded Microstructures with Electric Fields via Locally Altering Grain Boundary Complexions

TL;DR

This paper demonstrates how electric fields can be used to locally alter grain boundary complexions in ZnO, enabling the creation of continuously graded microstructures and advancing microstructural control in materials science.

Contribution

It introduces a novel method of using electric fields to manipulate grain boundary structures and microstructures, which was not previously achievable with traditional temperature and doping controls.

Findings

Electric fields induce cation-deficient, oxygen-rich grain boundaries near the anode.

Field-driven redistribution of cation vacancies verified by spectroscopy.

Gradual grain growth towards the anode without abnormal grain growth.

Abstract

Tailoring microstructures represents a daunting goal in materials science. Here, an innovative proposition is to utilize grain boundary (GB) complexions (a.k.a. interfacial phases) to manipulate microstructural evolution, which is challenging to control via only temperature and doping. Herein, we use ZnO as a model system to tailor microstructures using applied electric fields as a new knob to control GB structures locally via field-driven stoichiometry (defects) polarization. Specifically, continuously graded microstructures are created under applied electric fields. By employing aberration-corrected scanning transmission electron microscopy (AC STEM) in conjunction with density functional theory (DFT) and ab initio molecular dynamics (AIMD), we discover cation-deficient, oxygen-rich GBs near the anode with enhanced GB diffusivities. In addition, the field-driven redistribution of cation vacancies is deduced from a defect chemistry model, and subsequently verified by spatially resolved photoluminescence spectroscopy. This bulk stoichiometry polarization leads to preferential formation of cation-deficient (oxidized) GBs near the anode to gradually promote grain growth towards the anode. This mechanism can be utilized to create continuously graded microstructures without abnormal grain growth typically observed in prior studies. This study exemplifies a case of tailoring microstructural evolution via altering GB complexions locally with applied electric fields, and it enriches fundamental GB science.