Highly Mixed Index Facet Engineering Induces Defect Formation and Converts the Wave‐Transmissive Mott Insulator NiO into Electromagnetic Wave Absorbent

Abstract Mott insulator possesses the property of converting into semiconductor under supernormal conditions and achieving the Mott insulator‐semiconductor transition (IST) holds great scientific value. Nevertheless, current IST methodologies possess certain limitations because they are not capable of being implemented under conventional conditions, thereby limiting their practical applications. Herein, a highly mixed index facets (HMIF) strategy is proposed to construct homogeneous interfaces with gradient work function (WF) in Mott insulator NiO, accompanied by numerous oxygen vacancies. These vacancies provide additional defect energy levels and inhomogeneous charge distributions, resulting in a 180 fold enhancement of conductivity, realizing the IST process, and inducing the defect polarization. In addition, HMIF configuration induces electron transport along the index facets with gradient WF, ultimately leading to accumulation on the specific facet. This accumulation allows this facet can be considered as a dipole with its adjacent facets and makes NiO to attenuate electromagnetic waves (EMW) through dipole polarization. Therefore, NiO with exposed HMIF possesses improved EMW absorption properties (80‐fold higher than that of commercial NiO), realizing the transition from EMW‐transmissive to EMW‐absorbing materials. This research presents an approach for the IST process, discovers the polarization behavior that occurred on specific index facet, and extends its potential application in EMW absorption.