Huge permittivity with decreasing dissipation factor and humidity sensing properties of CaCu2.9Mg0.1Ti4.2-xGexO12 ceramics

CaCu2.9Mg0.1Ti4.2-xGexO12 ceramics with x=0, 0.1, and 0.2 were fabricated to study the electrical and dielectric properties, nonlinear current–voltage properties, humidity sensing properties. The main phase of CaCu3Ti4O12 (CCTO) was obtained in the sintered ceramics with dense microstructure and slight change in grain size. All sintered ceramics showed high dielectric permittivity (ε′ > 104) at frequencies below 105 Hz, while the loss tangent was reduced by a factor of 3 (from 0.034 to 0.010 at 1 kHz and 25°C), as x increased from 0 to 0.1. The temperature dependence of ε′ was also reduced. Furthermore, the enhanced nonlinear coefficient (α = 4.8–5.9) and breakdown electric field (Eb = 227–755 V/cm) were achieved. The dielectric and nonlinear properties originated from the electrically heterogeneous microstructure, which was confirmed by impedance and admittance spectroscopies. Both the resistance and activation energy of the insulating internal barriers were higher than that of the semiconducting core grains. Furthermore, these two parameters of the doped samples were larger than that of the undoped sample (x = 0). It was found that a low frequency ε′ was strongly dependent in the relative humidity in the range of 11–95 %RH, which could be applied in a humidity sensor. Accordingly, the hysteresis error was also calculated to determine the possibility of application in humidity sensors.