Size-Dependent Structural Phase Transition Behaviors of CaF2 Nanocrystals [CaF2纳米晶粒结构相变行为的尺寸依赖性]

作者：Gong L.; Wang J.^*; Zhang J.; Chen G.; Zhang H.; Wu X.; Hu T.; Cui H.

来源：Chinese Journal of High Pressure Physics, 2022, 36(2): 021102.

DOI：10.11858/gywlxb.20210842

• CaF2 nanocrystals
• High pressure
• Phase transition
• Size effect
• X-ray diffraction

CaF2 nanocrystals with a size of 11 nm have been investigated using X-ray diffraction technique under high pressure. A phase transition from the fluorite structure to the α-PbCl2-type structure has been observed at 12 GPa, which is much higher than the value observed in the bulk CaF2 and slightly lower than the one in smaller-sized CaF2 nanocrystals. The compressibility of the CaF2 nanocrystals is discussed, an obviously higher incompressibility than the bulk CaF2 is observed. The α-PbCl2-type metastable phase is retained when the pressure is released to ambient conditions. The unique high-pressure behaviors of the 11 nm-sized CaF2 nanocrystals are attributed to defects and grain size effect. The grain size effect is considered to be the main factor influencing the high-pressure behaviors of the CaF2 nanocrystals. When the size of the CaF2 nanocrystals is as small as 11 nm, the higher surface energy leads to the enhancement of the structural stability and the increase of the bulk modulus.

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