Effect of Mg2+ and Sr2+ doping on dielectric and non-ohmic properties in binary compound CaCu3Ti4O12/TiO2 ceramics

To improve the dielectric response of capacitive CaCu3Ti4O12/TiO2 ceramics (referred to as CaCu3Ti4.2O12 and abbreviated as Ti02), ceramics were single-doped with either Sr2+ or Mg2+ ions and co-doped with Sr2+ and Mg2+ ions. Systematically, the effects of single- and co-substitution of Sr2+ or Mg2+ and (Sr2+, Mg2+) ions on the dielectric constant (ε′), loss tangent (tanδ) and nonlinear properties of Ti02 fabricated by a polymer pyrolysis solution method were investigated. X-ray diffraction analysis showed the cubic perovskite crystalline phase of all prepared ceramics identified within the space group Im-3. It was found that the grain size of Ti02 decreased substantially with (Sr2+, Mg2+) co-doping. Additionally, (Sr2+, Mg2+) co-doped Ti02 had higher dielectric thermal stability than either Sr2+ or Mg2+-doped Ti02. Moreover, the co-doped Ti02 revealed a large dielectric response over extended ranges of frequency and temperature, as demonstrated by its outstanding ε′ value of ∼ 4 × 104 from 102–105 Hz and 20–210 °C, respectively. A very high breakdown field (Eb) value of ∼ 2579.25 V.cm−1 with a non-linear coefficient (α) of ∼ 10.01 and a minimal tanδ value of ∼ 0.033 were achieved in a co-doped MgSr05-1 ceramic. The noticeable increase in grain boundary resistance (Rgb) due to a decreased mean grain size and improved potential barrier heights (ΦB) in all doped Ti02 were responsible for the reduced tanδ and superior dielectric thermal stability.