Tunable current-voltage characteristics in polycrystalline calcium copper titanate

The nonlinear current-voltage relationship and the subsequent threshold voltage in polycrystalline CaCu3Ti4O12 are found to be easily controlled by simply doping a small amount of supervalent cations, Nb5+ and Ta5+. The authors show that the dopants have a significant effect on the reduction of the electrostatic potential at the grain boundaries, scarcely changing the conductance of the bulk grains. Through microcontact analysis and impedance spectroscopy, the control of the potential barrier at the boundaries was demonstrated to be a key factor for governing the overall current-voltage characteristics. Plausible compensation mechanisms for the excess charge of the added dopants are also discussed.(c) 2007 American Institute of Physics.