Effects of multiple cations and sintering temperature on microstructure and dielectric properties in NaLnCuTiO (Ln = Sm and Eu) ceramic materials.

NaEuCuTiO and NaSmCuTiO 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, Eu) co-doped ceramics changed faster than that of (Na, Sm) co-doped ceramics. Abnormally high dielectric constants of ~ 3.17 × 10 and ~ 1.06 × 10 (at 10 Hz and 303 K) were achieved in NaSmCuTiO and NaEuCuTiO ceramics prepared at 950 °C, respectively. However, NaSmCuTiO and NaEuCuTiO 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 CaCuTiO-based ceramics.