Nonlinear current–voltage behavior in La-doped CaCu3Ti4O12 thin films derived from sol–gel method

Abstract

The effect of La3+ doping at Ca2+ sites in CaCu3Ti4O12 (CCTO) thin film was investigated. Samples with compositions of Ca(1−3x/2)LaxCu3Ti4O12 (x = 0, 0.05, 0.1, 0.15 and 0.2) were synthesized by sol–gel method. Remarkable non-Ohmic behaviors in all the samples were presented through a semiconductor parameter analyzer. Results showed that with the increase of dopant’s amount, the threshold voltage of CCTO thin films firstly increased and then decreased and the nonlinear coefficient decreases, good thermal and electric stability was found in all samples. XRD results confirmed the single phase formation of all the samples with similar cubic structure of CCTO and characterization with SEM showed a completely opposite trends between the grain size and the threshold voltage. The double Schottky barrier model is used to explain the nonlinearity of CCTO thin films and the relationship between grain size and threshold voltage in the thin films. The presence of Schottky barrier at the grain boundary is confirmed by a linear relationship between ln(J) and E1/2. A possible way is put forward to control the non-Ohmic properties of CCTO thin films based on this research.