Transport properties of mixing conduction in CaF2 nanocrystals under high pressure**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374131, 11674404, 11404137, and 61378085), Program for the Development of Science and Technology of Jilin Province, China (Grant Nos. 201201079 and 20150204085GX), Twentieth Five-Year Program for Science and Technology of Education Department of Jilin Province, China (Grant No.

Abstract

We report on the intriguing electrical transport properties of compressed CaF2 nanocrystals. The diffusion coefficient, grain and grain boundary resistances vary abnormally at about 14.37 GPa and 20.91 GPa, corresponding to the beginning and completion of the Fm3m–Pnma structural transition. Electron conduction and ion conduction coexist in the transport process and the electron conduction is dominant. The electron transference number of the Fm3m and Pnma phases increases with pressure increasing. As the pressure rises, the F− ion diffusion and electronic transport processes in the Fm3m and Pnma phases become more difficult. Defects at grains play a dominant role in the electronic transport process.