Effects of multiple cations and sintering temperature on microstructure and dielectric properties in...

Na_1/2Eu_1/2Cu₃Ti₄O₁₂ and Na_1/2Sm_1/2Cu₃Ti₄O₁₂ dielectric ceramics were synthesized at different sintering temperatures (950, 975 and 1000 °C) by a solid-state reaction method. Phase structure, cation valence state, and dielectric properties of all sintered ceramics were systematically investigated. When the preparation temperature was changed, the Cu⁺ ion concentration of (Na⁺, Eu³⁺) co-doped ceramics changed faster than that of (Na⁺, Sm³⁺) co-doped ceramics. Abnormally high dielectric constants of ~ 3.17 × 10⁴ and ~ 1.06 × 10⁴ (at 10 Hz and 303 K) were achieved in Na_1/2Sm_1/2Cu₃Ti₄O₁₂ and Na_1/2Eu_1/2Cu₃Ti₄O₁₂ ceramics prepared at 950 °C, respectively. However, Na_1/2Sm_1/2Cu₃Ti₄O₁₂ and Na_1/2Eu_1/2Cu₃Ti₄O₁₂ prepared in high sintering temperature (1000 °C) exhibited a good frequency stability of dielectric permittivity. It was demonstrated that an increasing number of charge carriers induced by the increase of sintering temperature could lead to a competitive coexistence of two polarization mechanisms (surface barrier layer capacitor and internal barrier layer capacitor), further changing the dielectric properties of CaCu₃Ti₄O₁₂-based ceramics.