Structural transition of BaF sub(2) nanocrystals under high pressure

The structural transition of BaF sub(2) nanocrystals is studied by in situ high pressure synchrotron radiation X-ray diffraction measurements up to about 21.2 GPa at ambient temperature. Two phase transformations were observed at 5.8 and 14.4 GPa, and the two high pressure phases are identified as orthorhombic (Pnma) phase and hexagonal (P6 sub(3)/mmc) phase by Rietveld refinement. Upon decompression, the alpha -PbCL sub(2)-type metastable phase is retained when the pressure is released. Two phase transformations of the BaF sub(2) nanocrystals are higher than that in bulk BaF sub(2). It is proposed that the size effects are found to influence the BaF sub(2) nanocrystals high-pressure behaviors and the surface energy plays a significant role in the structural stability.