摘要
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CaF_2(平均粒度为16nm)和Ca_(0.75)La_(0.25)F_(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CaF_2的离子电导率比多晶CaF_2约高1个数量级、比单晶CaF_2高2个数量级,离子导电激活能△E=1.14eV;3)纳米Ca_(0.75)La_(0.25)F_(2.25)的离子电导率比纳米CaF_2高1(300℃)至0.6(525℃)个数量级,激活能△E=1.00eV,略低于纳米CaF_2;4)从250℃升至525℃两种纳米离子导体的晶粒电阻下降约一个数量级,晶界电阻单调下降4个多数量级。表明F^-迁移在低温区(<400℃)为晶粒扩散,在高温区(>450℃)转变为晶界扩散。综上所述,将材料晶粒度减小至纳米尺度和掺杂都可明显提高离子电导率。
Two kinds of nanocrystalline materials CaF2(grain fineness D =16nm) and Ca(0.75)La(0.25)
F(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(0.75)La(0.25)F(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.
出处
《物理学报》
SCIE
EI
CAS
CSCD
北大核心
1993年第6期969-977,共9页
Acta Physica Sinica
基金
国家自然科学基金
国家高技术研究发展计划资助项目
国家科委基础处资助的课题
