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All‐inorganic lead halide perovskite nanocrystals (NCs) have shown great potential in various optoelectronic device applications due to their excellent optoelectronic properties, but their poor stability remains a key obstacle to widespread application. The preparation of core/shell NCs is developed to improve their stability, but most of the coating for single NCs is incomplete, and the crystal orientation and interface binding of core/shell structures are still unclear. Here, a surface reconstruction strategy to synthesize CsPbBr3/CsPb2Br5 core/shell NCs with uniform coating structure is reported. The concentration of [PbBr8]6− monomer in the system is regulated by creating local low H2O concentration conditions to balance the erosion of perovskite by water and the overall heterogeneous nucleation reaction system, resulting in single encapsulated and well‐edged perovskite core/shell NCs. More importantly, advanced characterization tools are used to reveal the core/shell structural features of CsPbBr3/CsPb2Br5 core/shell NCs at the atomic scale, which has not been reported before, and the interface matching of the two‐phase binding is simulated by density functional theory calculations, which confirm that the CsPb2Br5 (116) facet can bind to the CsPbBr3 (100) facet with the lowest binding energy. The prepared core/shell perovskite NCs can still retain photoluminescence emission after >30 days in water. [ABSTRACT FROM AUTHOR]

The discovery of unconventional scale-free ferroelectricity in HfO 2 -based fluorite thin films has attracted great attention in recent years for their promising applications in low-power logic and nonvolatile memories. The ferroelectricity of HfO 2 is intrinsically originated from the widely accepted ferroelectric metastable orthorhombic Pca 2 1 phase. In the last decade, defect-doping/solid solution has shown excellent prospects in enhancing and stabilizing the ferroelectricity via isovalent or aliovalent defect-engineering. Here, the recent advances in defect-engineered HfO 2 -based ferroelectrics are first reviewed, including progress in mono-ionic doping and mixed ion-doping. Then, the defect-lattice correlation, the point-defect promoted phase transition kinetics, and the interface-engineered dynamic behaviour of oxygen vacancy are summarized. In addition, thin film preparation and ion bombardment doping are summarized. Finally, the outlook and challenges are discussed. A multiscale structural optimization approach is suggested for further property optimization. This article not only covers an overview of the state-of-art advances of defects in fluorite ferroelectrics, but also future prospects that may inspire their further property-optimization via defect-engineering.