AI 中文总结
该研究构建了静水压下化学计量双层镍酸盐La3Ni2O7的单晶压力-温度结构相图，明确其在约10 GPa发生结构相变并伴随超导出现，为镍酸盐超导微观理论提供结构基础。
AI 中文摘要
双层镍酸盐La3Ni2O7因高压下发现高温超导电性而受到广泛关注，它是首个体相形式的镍酸盐超导体。但超导相的晶体结构仍在积极探讨中，这阻碍了其微观起源的研究。本文通过构建确定的压力-温度相图解决这些结构争议，其中包含使用氦作为传压介质的静水压条件下化学计量La3Ni2O7单晶的超导区域。常压下，La3Ni2O7采用极性正交晶系Am2m结构，具有不等价Ni位之间的电荷有序和NiO6八面体倾斜特征。压缩时，该系统在约10 GPa附近从电荷有序的Am2m相直接转变为四方晶系I4/mmm相，同时伴随体相超导的出现。这些结果明确了La3Ni2O7的本征结构演化，为镍酸盐超导电性的微观理论提供了结构框架。
英文摘要
The bilayer nickelate La3Ni2O7 has attracted intense interest following the discovery of high-temperature superconductivity under pressure, representing the first nickelate superconductor realized in bulk form. However, the crystal structure of the superconducting phase remains under active discussion, complicating efforts to establish its microscopic origin. Here we resolve these structural controversies by establishing a definitive pressure-temperature phase diagram, including the superconducting region of stoichiometric La3Ni2O7 single crystals under hydrostatic conditions using helium as the pressure-transmitting medium. At ambient pressure, La3Ni2O7 adopts a polar orthorhombic Am2m structure characterized by charge order between inequivalent Ni sites and NiO6 octahedral tilting. Upon compression, the system undergoes a direct transition from the charge-ordered Am2m phase to the tetragonal I4/mmm phase near 10 GPa, coinciding with the onset of bulk superconductivity. These results establish the intrinsic structural evolution of La3Ni2O7 and provide a structural framework for microscopic theories of nickelate superconductivity.
