Functional CsPbI₃ perovskite phases are not stable at ambient conditions and spontaneously convert to a non-perovskite δ phase, limiting their applications as solar cell materials. We demonstrate the preservation of a black CsPbI₃ perovskite structure to room temperature by subjecting the δ phase to pressures of 0.1 – 0.6 GPa followed by heating and rapid cooling. Synchrotron X-ray diffraction and Raman spectroscopy indicate that this perovskite phase is consistent with orthorhombic γ-CsPbI₃. Once formed, γ-CsPbI₃ could be then retained after releasing pressure to ambient conditions and shows substantial stability at 35% relative humidity. First-principles density functional theory calculations indicate that compression directs the out-of-phase and in-phase tilt between the [PbI₆]⁴⁻ octahedra which in turn tune the energy difference between δ- and γ-CsPbI₃, leading to the preservation of γ-CsPbI₃. Here, we present a high-pressure strategy for manipulating the (meta)stability of halide perovskites for the synthesis of desirable phases with enhanced materials functionality.

Surface lattice reconstruction is commonly observed in nickel-rich layered oxide battery cathode materials, causing unsatisfactory high-voltage cycling performance. However, the interplay of the surface chemistry and the bulk microstructure remains largely unexplored due to the intrinsic structural complexity and the lack of integrated diagnostic tools for a thorough investigation at complementary length scales. Herein, by combining nano-resolution X-ray probes in both soft and hard X-ray regimes, we demonstrate correlative surface chemical mapping and bulk microstructure imaging over a single charged LiNi_0.8Mn_0.1Co_0.1O₂ (NMC811) secondary particle. We reveal that the sub-particle regions with more micro cracks are associated with more severe surface degradation. A mechanism of mutual modulation between the surface chemistry and the bulk microstructure is formulated based on our experimental observations and finite element modeling. Such a surface-to-bulk reaction coupling effect is fundamentally important for the design of the next generation battery cathode materials.

M_n+1AX_n phases exhibit unique laminated atomic structures that result in properties typical of both ceramics and metals. Due to their unusual characteristics, these materials have been proposed for use in a wide variety of industrial applications, including in nuclear reactors—both fission and fusion systems—where they will be exposed to extreme irradiation conditions and high temperatures. Recently, numerous studies have investigated radiation effects on the M_n+1AX_n phases, revealing complex behavior—phase transformations, surface modification, and mechanical property changes—induced by ion or neutron irradiation over a range of temperatures. This review summarizes recent experimental and theoretical work on the response of the M_n+1AX_n phases to irradiation and discusses the intrinsic controls on the radiation tolerance of these materials. Based on the review of the present body of work, a comprehensive understanding of the mechanisms of irradiation-induced structural modification and defect evolution in M_n+1AX_n phases is developed, as well as proposed strategies for designing novel M_n+1AX_n phases with enhanced performance under extreme irradiation conditions.

In fusion reactors, 14 MeV high-energy neutron irradiation of structural materials will produce large amounts of helium and hydrogen simultaneously with displacement defects. These He and H atoms will interact with displacement defects, leading to He-H synergistic effects and aggravating the irradiation damage. Currently, there exist no available high-flux fusion neutron sources. Additionally, the neutron energy spectrum and the generation of He and H in fission reactors or spallation neutron sources greatly differ from those in fusion reactors. Multi-ion beam irradiation is a promising method to emulate the synergistic effects induced by fusion neutron irradiation. This review summarizes the experimental studies on the He-H synergistic effects, and analyzes the effects of He and H on cavity evolution and swelling under multi-ion beam irradiation. The roles of various experimental factors are also discussed. More systematically controlled experiments are suggested to develop a comprehensive understanding of He-H synergistic effects in structural materials.