Microstructure and electrical properties of calcium copper titanate ceramics

The effect of stoichiometry, i.e. Ca/Cu ratios (CaCu_3xTi ₄O₁₂, x = 0.8, 0.9, 1.0, 1.1 and 1.2) on the microstructure and electrical properties was investigated. The grain sizes of CaCu_3XTi₄O₁₂ composition increased sharply with the increase of copper, from ∼1 μm with x = 0.8 to ∼50 ∼m 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 CaCu_3XTi₄O₁₂ composition is not consistent with the amount of copper and cell parameters and grain sizes. Impedance spectroscopy exhibited that the CaCu_3XTi ₄O₁₂ composition had two semicircle at least at high frequency (∼ 10 Hz) and low frequency (〈100 Hz), respectively. The grain and grain boundary of the compositions had different impedance and relaxation behavior.