Modification of Cu-deficient CaCu2.8Ti4O12 ceramics via Mg2+ substitution at Cu sites for improved dielectric properties and thermal stability

Abstract

Mg2+ substitution at the Cu sites of Cu-deficient CaCu2.8-xMgxTi4O12 (x = 0.00, 0.05, and 0.10) ceramics was accomplished using a polymer pyrolysis technique. The nonlinear and dielectric properties of all ceramics under various sintering temperatures were investigated. Very low tanδ ∼ 0.011–0.030 and giant ε′ ∼ 4406–13,521 were obtained in these ceramics. Surprisingly, excellent thermal stability, where ε′ remained within± 15% and is adequate for X8R capacitors, is obtained in CaCu2.75Mg0.05Ti4O12 and CaCu2.7Mg0.1Ti4O12 ceramics sintered at 1100 °C for 8 h. Additionally, the nonlinear J-E properties were improved compared to an unmodified sample. Interestingly, a nonlinear coefficient (α) of ∼ 58.05 in the CaCu2.75Mg0.05Ti4O12 ceramic sintered at 1100 °C for 8 h is acceptable for varistor applications. Improvement of nonlinear and dielectric properties arise from the electrical interface responses altered by Mg2+ substitution. The ceramics were characterized using XRD, TEM and FE-SEM techniques to investigate their crystal structure and microstructure. EDXS results confirmed the coexistence of TiO2 and CaTiO3 phases in all ceramics. It was suggested that the enhancement of grain boundary resistance (Rgb) with simultaneously improved electrical and nonlinear J-E behaviors caused by the alternation of electrical interface responses at GBs. XPS measurements of these ceramics presented Cu3+/Cu2+/Cu+ ratios that indicate the semiconducting properties of grains.