The effect of Eu 2O 3 doping on CaCu 3Ti 4O 12 varistor properties

Abstract

The CaCu 3Ti 4O 12 ceramics varistors doped with different proportions of Eu 2O 3 dopant (wt%, x = 0, 0.2%, 0.5%, 1%) are prepared by the traditional solid-state reaction method. SEM and XRD are used in the microstructural studies of the specimens. A high voltage measuring unit and Agilent 4294A Precision Impedance Analyzer are used to determine the nonohmic ( J–E) behaviors and measure the dielectric properties and the complex impedance of the varistors. The results show that Eu 2O 3 doping can reduce the mean grain size and can also deter the formation of Cu-rich phases at the grain boundaries. The second phase of CuO is present in the XRD pattern of pure CCTO but disappears in that of the samples doped with Eu 2O 3. More smaller grains appear around big grains when CCTO is doped with Eu 2O 3, a much closer touch of the crystal grains is made, which results in the stability of dielectric properties dependent on frequency. Eu 2O 3 doping can enhance the height of the Schottky barriers at interfaces between grains, which not only has greatly raised the nonlinear coefficient and the breakdown voltage but also significantly improved the frequency stability of dielectric properties of the CCTO varistors. The results of the impedance spectrum support the model of Schottky barrier proposed to explain the nonohmic behavior and the dielectric properties of CCTO.