Selective Ions Exchange Reactions Endow Defective Heterovalent Copper‐Based Selenides With Enhanced Dielectric Polarization Response

Abstract Defective heterovalent selenides provide a spacious arena for creating emergent electromagnetic (EM) phenomena that are unattainable in the conventional constituent counterparts. However, there are still synthetic methodological challenges, and in‐depth understanding of the EM properties, particularly correlation between tailored polarization sites and dielectric polarization response, are significantly inadequate. Herein, a selective ions exchange strategy driven by concentration‐regulated (Case 1) and time‐evoked (Case 2) approaches, is innovatively proposed to design series of defective heterovalent copper‐based selenides. The controllable phase evolution tailored by concentration‐regulated mixed cation/anion exchange is responsible for heterointerfaces levels (Case 1), while Cu⁺/Cu²⁺ electronic configurations controlled by time‐evoked cation exchange accounted for further manipulating heterointerfaces/defects levels and enriching polarization sites (Case 2). The coupling of nonstoichiometric Cu_2−xSe‐containing heterointerfaces, unsaturated Se vacancies and multi‐valence configurations, rather than themselves alone even at a higher level, imparted abundant polarization sites to trigger boosted polarization response for defective heterovalent selenides. Consequently, this designed defective heterovalent selenide (ZnSe/CuSe/Cu_2‐xSe) deliveres a broad bandwidth of 6.89 GHz compare to parent ZnSe without dielectric response, outperforming most reported metal selenides until now. This innovative strategy overcame the bottlenecks of conventional synthetic methodology, providing a paradigm for fabricating sophisticated defective heterovalent materials for versatile applications beyond EM absorption.