Electrical properties of Li-doped Bi2/3Cu3Ti4O12 ceramics

Li-doped Bi2/3Cu3Ti4O12 ceramics were successfully prepared using a conventional solid-state method. As the Li content increases, the lattice constant gradually decreased and the grain size increased. The analysis of energy-dispersive spectrometer and elemental mapping suggested that the grain boundaries are enriched with CuO. The frequency dependence of the dielectric constant and loss exhibited a two-stage step-like decline. Three different dielectric characteristics were observed in the low-, mid-, and high-frequency ranges. In the mid-frequency range from 5 to 100 kHz, the dielectric constant was effectively improved by Li doping, and the dielectric loss gradually decreased with increasing Li doping. The complex impedances of all compositions present three distinct semi-arcs. Combined with the analysis of dielectric and impedance properties under DC bias, it was concluded that the dielectric responses of all Li-doped Bi2/3Cu3Ti4O12 ceramics at low, intermediate, and high frequencies originated from the electrode, grain boundary, and grain effects, respectively. The resistances of the different regions are calculated by impedance fitting. The study of the frequency dependence of dielectric properties, electric modulus, and impedance at various temperatures further verified the existence of electrode, grain boundary, and grain relaxations. X-ray photoelectron spectroscopy reveals that the increase in conductivity at high frequencies with increasing Li content was contributed to an jump of electrons between Cu+ and Cu2+.