Rare earth doped CaCu3Ti4O12 electronic ceramics for high frequency applications

Ca1-xRxCu3Ti4O12 (R=La, Y, Gd; x=0, 0.1, 0.2, 0.3) electronic ceramics were fabricated by conventional solid-state reaction method. The microstructure and dielectric properties as well as impedance behavior were carefully investigated. XRD results showed that the secondary phases with the general formula R2Ti2O7 existed at grain boundaries of rare earth doped ceramics, which inhibited abnormal grain growth. The dielectric constant decreased from 4x10(5) in pure CaCu3Ti4O12 (CCTO) ceramics to 2x10(3) with rare earth doping. However, all samples showed high dielectric constant in broad frequency range (<10 MHz). The cutoff frequency (f(0)) was remarkably shifted to higher frequency from 13 MHz (pure CCTO ceramics) to 80 MHz (Gd-doped CCTO ceramics). Meanwhile, the dielectric loss tangent rapidly decreased approximately 10 times. These improvements of dielectric properties by rare earth doping are very useful in wide frequency chip capacitor and LTCC devices.