High-Pressure Behaviors of SrF2 Nanocrystals with Two Morphologies

Using an in situ synchrotron angle-dispersive X-ray diffraction technique, two morphologies of nanocrystalline SrF2 (i.e., nanoparticles and nanoplates) with different sizes of 11 and 21 nm were compressed up to ∼46 GPa in diamond anvil cells at room temperature. We observed that two phase transitions of the SrF2 nanoparticles occur at 10.0 and 34.3 GPa, which are much higher than those in bulk SrF2. Upon decompression, the pure α-PbCl2-type metastable phase is retained when the pressure is released. In contrast, high-pressure behavior of the SrF2 nanoplates is similar to that of bulk material. Such distinct high-pressure behaviors in two synthesized SrF2 nanocrystals have been discussed in terms of volume expansion, exposed crystal plane, morphology, and defects. Further analysis shows that the defect effect is believed to be the major factor to affect the high-pressure behaviors in two synthesized nanocrystalline SrF2.