The effect of stoichiometry, i.e. Ca/Cu ratios (CaCu3xTi4O12, x = 0.8, 0.9, 1.0, 1.1 and 1.2)
on the microstructure and electrical properties was investigated. The grain sizes of CaCu3xTi4O12
composition increased sharply with the increase of copper, from ~1 μm with x = 0.8 to ~50 μm with x
= 1.2. The real part of dielectric permittivity changed dramatically, the pellet with x = 1.0 had the
highest dielectric permittivity ~160, 000 at 1 kHz. Furthermore, the dielectric permittivity of all
pellets was impressively large values (between 10, 000 to 1, 000,000 at 100 Hz) and was nearly
constant over a wide frequency range between 100 Hz to ~100 MHz. However, the dielectric
permittivity of CaCu3xTi4O12 composition is not consistent with the amount of copper and cell
parameters and grain sizes. Impedance spectroscopy exhibited that the CaCu3xTi4O12 composition
had two semicircle at least at high frequency (~ 107 Hz) and low frequency (<100 Hz), respectively.
The grain and grain boundary of the compositions had different impedance and relaxation behavior.