Selectivity of doping ions to effectively improve dielectric and non-ohmic properties of CaCu3Ti4O12 ceramics

We provide two separate strategies to improve the dielectric properties of CaCu3Ti4O12 ceramics. First, substitution of La3+ ions can reduce the loss tangent (tanδ<0.03) and increase the temperature stability of the dielectric constant (Δε′(%)) of CaCu3Ti4O12 ceramics. The dielectric constant of CaCu3Ti4O12 was greatly reduced from ∼17500 to ∼5300 and ∼2700 for Ca0.775La0.15Cu3Ti4O12 and Ca0.70La0.2Cu3Ti4O12, respectively. The Δε′(%) values of these two ceramics were found to be approximately ±15% over the temperature ranges of −55–125 °C and −55–150 °C, meeting X7R and X8R temperature characteristics for capacitor applications, respectively. Second, substitution of Sr2+ at concentrations of 5–15 at% can significantly reduce tanδ (<0.04). Interestingly, the dielectric constant decreased slightly and was found to be higher than 104. However, the requirement for Δε′<±15% was obtained only over the −60–90 °C temperature range. The effects of La3+ and Sr2+ doping ions on the nonlinear current–voltage properties were also investigated. Both doping ions were observed to significantly enhance nonlinear electrical properties.