Nanocrystalline CaCu_3Ti_4O_(12) powder by PVA sol-gel route: synthesis, characterization and its giant dielectric constant

摘要

Nanocrystalline CaCu_3Ti_4O_(12) powders were synthesized by a simple PVA sol-gel route and calcined at 700 and 800℃ in air for 8 h. The diameter of the powders ranges from 40-100 nm. The calcined CaCu_3Ti_4O_(12) powders were characterized by TG-DTA, XRD, FTIR, SEM, and TEM. Sintering of the powders was conducted in air at 1100℃ for 16 h. The XRD results indicated that all sintered samples had a typical perovskite CaCu_3Ti_4O_(12) structure although the sintered samples contained some amount of CaTiO_3. SEM of the sintered CaCu_3Ti_4O_(12) ceramics showed the average grain sizes of 13-15 urn. The samples exhibit a giant dielectric constant, ε' ～ 10~5 at 150 to 200℃ with weak temperature dependence below 1 kHz in the sample sintered using the powders calcined at 700℃. The Maxwell-Wagner polarization mechanism is used to explain the high permittivity in these ceramics. It is also found that all sintered samples have the same activation energy of grains, which is ～0.122 eV.