纳米CaF2离子电导率和介电常数与流体静压力的关系

 采用惰性气体蒸发和真空原位加压方法，制备了具有清洁界面的平均粒度为14 nm的纳米固体CaF₂，并在0.1 MPa～2.2 GPa压力范围内52个不同的静水压下，分别详细测量出其离子电导率σ和相对介电常数随压力变化的规律。讨论指出：（1）离子迁移通道受压后的变化（大于、等于或小于最佳值），是影响离子电导率-压力曲线峰值的主要因素；（2）当压力从0.66 GPa再增加时，lg σ分三段线性下降，可归因于纳米晶体的三种自由体积；（3）界面层空间电荷极化是造成纳米CaF₂相对介电常数较大的原因，由此可理解介电常数的压力效应，了提高产品的氟离子电导率，用真空原位加压法制备纳米材料时，应当采用高于0.66 GPa的压力。

RELATION OF HYDROSTATIC PRESSURE TO BOTH IONIC CONDUCTIVITY AND PERMITTIVITY OF NANOPHASE CaF2

A nanophase solid CaF2 with a clean interface and an average grain size of 14 nm was prepared by evaporating in inert gas and compacting in situ in high vacuum. Under different hydrostatic pressures ranging from 0.1 MPa to 2.20 GPa, the ionic conductivity (σ) and permittivity (κ) of the resulting product were measured to determine their relation to pressure. The results show: (1) The change caused by the pressure in the ionic migration channel (equal to, greater or smaller than the optimum) is the main factor that affects the peak of the ionic conductivity-pressure curve. (2) When pressure goes up from 0.66 GPa,lgσ drops linearly along 3 line segments, which may be ascribed to three kinds of free volumes in the nanometer-sized crystalline materials. (3) Polarization of space charge on the boundary layer is the main cause of the high relative permittivity of nanophase CaF2 , which illustrates the effect of pressure on permittivity. In order to obtain a compact bulk with higher fluorine ionic conductivity, a higher pressure of 0.66 GPa is recommended in the preparation of the nanophase material.