Grain Size and Defect Synergy in Pressure‐Induced Phase Transitions and Compressibility of SrF ₂ Nanocrystals

The structural stability and compressibility of 29 nm SrF ₂ nanocrystals under high pressure were investigated by in situ XRD. It was found that before the cubic‐to‐orthorhombic phase transition at 8.3 GPa, the size effect and grain morphology played a critical role, stabilizing the fluorite structure and resulting in a higher bulk modulus (96(4) GPa). Subsequent grain fragmentation produced numerous defects, thereby markedly increasing the material’s compressibility, as reflected by a lower bulk modulus of 59(3) GPa for the orthorhombic phase. The influence of these defects then became predominant, dictating the pressure of the ensuing orthorhombic‐to‐hexagonal transition at 27.5 GPa and the evolution of compressibility, with the hexagonal phase exhibiting a bulk modulus of 157(18) GPa. This study elucidates the synergetic effects of grain size and defects, providing a foundation for accessing new structures in SrF ₂ ‐based nanomaterials.