Enhanced dielectric response and non-Ohmic properties of Ge-doped CaTiO₃/CaCu₃Ti₄O₁₂

We present a method for increasing the dielectric constant of CaTiO3/CaCu3Ti4O12 (CTO/CCTO) composites and retaining a low-loss tangent (tanδ) by doping with Ge dopant. The Ge-doped CTO/CCTO composites were fabricated using a one-step processing method. The phase composition and microstructure analyses confirmed the existence of CTO and CCTO phases, in which Ge doping ions can be substituted into both phases. The mean grain sizes of the two phases were slightly reduced by decreasing the porosity. Doping the CTO/CCTO with Ge doping ions resulted in a high dielectric constant by ~ two times, while a very low tanδ value of ~0.01 did not change. Furthermore, the dielectric constant changed by less than ±15% in the temperature range of −60 – 150°C. The nonlinear current density–electric field properties of CTO/CCTO can also be enhanced. Impedance spectroscopy showed a heterogeneous microstructure with enhanced grain boundary properties after doping with Ge dopants, giving rise to enhanced nonlinear electrical properties. The decreased grain resistivity due to Ge substitution is confirmed to originate from the increase in the Ti3+/Ti4+ ratio, which was analyzed using X–ray photoelectron spectroscopy .