纳米CaF2和纳米Ca0.75La0.25F2.25的结构对离子电导率的影响

用惰性气体蒸发和真空原位加压方法制备了两种具有清洁界面的纳米离子固体CaF₂(平均粒度为16nm)和Ca_0.75La_0.25F_2.25(平均粒度为11nm),在31℃至530℃详细测量了其复阻抗谱。结果表明:1)在300—530℃两种纳米离子导体都很好地遵从Arrhenius方程式;2)纳米CaF₂的离子电导率比多晶CaF₂约高1个数量级、比单晶CaF₂

EFFECT OF STRUCTURE ON IONIC CONDUCTIVITY IN THE NANOCRYSTALLINE MATERIALS CaF2 AND Ca0.75La0.25F2.25

Two kinds of nanocrystalline materials CaF₂(grain fineness D =16nm) and Ca_0.75La_0.25F_2.25(D = 11nm) possessing clean interfaces were prepared with the method of inert gas evaporation and pressed under ultra high vacuum, Their complex impedance spectra were meas-sured in detail in the temperature range of 31℃ to 530℃. The results show that (1) In the range of 300℃ to 530℃, both of the two kinds of nanocrystalline ionic solids obey the Arrhe-nius equation well; (2) Ionic conductivity of nano-CaF₂ is about one order of magnitude higher than that of polycrystalline CaF₂, two order of magnitude higher than that of monocrystalline CaF₂, activation energy for ionic conduction, E=1.14eV; (3) Ionic conductivity of nano-Ca_0.75La_0.25F_2.25 is 1(300℃)-0.6(525℃) order of magnitude higher than that of nano-CaF₂, activation energy E is 1.00eV, somewhat lower than that of nano-CaF₂, (4) When the temperature rises from 250℃ to 525℃ , the resistance of grains drops about one order of magnitude, but the resistance of interfaces descends monotonously over four order of magnetude. It is demostrated that migration of F^- depends on diffusion among grains at temperature lower than 400℃, and also upon diffusion among interfaces at temperature higher than 450℃. To decrease grain fineness of materials to nanometer-size as well as to mingle fluoride with higher valence can increase the ionic conductivity obviously.