Yuning Liang, Bo Gao, Yonglong Zhu, Qun Xu
Abstract In ionic crystals, the simultaneous control of polarity compensation and exposure of high‐crystallinity surfaces has long been a critical bottleneck for modulating their interfacial electronic and spin properties. Using the typical ionic crystal KTaO 3 (KTO) as a model system, it is demonstrated that supercritical carbon dioxide (SC CO 2 ) treatment is an effective solution to this challenge. As the SC CO 2 pressure increases from 12 to 20 MPa, the surface of KTO gradually transforms from a rough, low‐index (001) facet into high‐crystallinity, high‐index polar facets, specifically (), (), and (111). Density functional theory (DFT) calculations indicate that this transformation primarily arises from the lower adsorption energy of CO 2 on high‐index facets, making these CO 2 ‐adsorbed high‐index surfaces thermodynamically more stable. Notably, CO 2 induces magnetic moments via polarity compensation mechanisms without introducing oxygen vacancies (O v ), thereby enhancing macroscopic magnetism with increasing pressure. This finding challenges the conventional view that magnetic moments in nominally nonmagnetic oxides are induced solely by O v . Therefore, the research demonstrates that SC CO 2 , as a green and scalable treatment strategy, can expose high‐crystallinity, high‐index facets through polarity compensation, thus offering a versatile platform for oxide facet engineering and polarity compensation studies.