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Project supported by the National Natural Science Foundation of China (Grant Nos. 11374131, 11674404, 11404137, and 61378085), the Program for New Century Excellent Talents in University, China (Grant No. NCET-13-0824), the Program for the Development of Science and Technology of Jilin Province, China (Grant Nos. 201201079 and 20150204085GX), and the Twentieth Five-Year Program for Science and Technology of Education Department of Jilin Province, China (Grant No. 20150221).
The charge transport behavior of strontium fluoride nanocrystals has been investigated by in situ impedance measurement up to 35 GPa. It was found that the parameters changed discontinuously at each phase transition. The charge carriers in SrF2 nanocrystals include both F
Nanoscale materials have recently attracted considerable attention due to their special properties that are different from those of bulk materials.[1–4] In general, a decrease in crystal size implies an increased proportion of the surfaces (interfaces) and usually also in increased grain boundary (GB) properties. Therefore, the nanoscale material may have some unique transport properties that would not be presented in the bulk material, which is worth exploring.
The solid fluoride materials have been paid a great deal of attention due to their unique properties, such as low-energy phonons, high ionicity, electron–acceptor behavior, high resistivity, and anionic conductivity.[5–7] These properties lead to a wide range of potential applications in optics, biological labels, and lenses,[8,9] as well as components of insulators, gate dielectrics, wide-gap insulating overlayers, and buffer layers in semiconductor-on-insulator structures.[10] Alkaline earth metal fluorides have been extensively used as solid electrolytes to measure fluorine chemical potentials at high temperatures, and thus, to determine the Gibbs free energies of the formation of metal fluorides, oxides, carbides, and sulfides.[11,12] Their ambient and moderate temperature conductivities are relatively low.[13] This is a limitation of the use of alkaline earth metal fluorides as practical electrolytes for low temperature operations. In recent years, it was found that the F
In this paper, we conducted an alternate-current (AC) impedance measurement of SrF2 nanoplates at high pressures up to 35 GPa. The conduction mechanism involved in the charge transport process was studied.
In-situ impedance spectroscopy measurements of SrF2 nanoplates were conducted at high pressure using a diamond anvil cell (DAC). The diamond culet face was
A T301 stainless steel was pre-indented into
The Nyquist representation of the impedance spectroscopy of SrF2 nanoplates under various pressures is shown in Fig.
As accepted for a solid sample, the equivalent circuit method is a reliable approach to describe the impedance spectra. To the bulk SrF2, the charge carriers are F
The agreement of the simulated spectra with the experimental data [Fig.
![]() | Fig. 5. Relationships of grain resistance, grain boundary resistance and grain relaxation frequency versus pressure. |
From Fig.
In the
Puin et al. measured the conductivity of nanocrystalline CaF2 at temperatures from 390 K to 500 K and found that the charge carriers are only F
The electron carrier transport in SrF2 nanoplates grains can be regarded as a charging process in an
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![](cpb_26_4_046401/cpb_26_4_046401_ieqn0026.gif)
![]() | Table 1.
Pressure dependence of grain activation energy. . |
It can be seen that the activation energy decreases with increasing pressure in the
The charge transport behavior of strontium fluoride nanoplates has been investigated by in-situ impedance measurement at pressures up to 35 GPa. Each parameter changes discontinuously at about 6.71 GPa and 27.56 GPa, corresponding to the phase transitions of SrF2 nanoplates under high pressure. The charge carriers in SrF2 nanocrystals include both F
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