Influence of MnCO₃ additive on the dielectric properties of BaCuB₂O₅-doped Ba_4.5(Nd_0.7Sm_0.3)₉Ti₁₈O₅₄ ceramics sintered in a reducing atmosphere

Sintered in a reducing atmosphere, the dielectric properties of Ba_4.5(Nd_0.7Sm_0.3)₉Ti₁₈O₅₄ (BNST) ceramics are deteriorated because of the ionized oxygen vacancies and conduction electrons. The feasibility of reduction resistance in BNST ceramics sintered in a reducing atmosphere was investigated in this work. Prompted by the example of BaTiO₃ ceramics used in base-metal electrode multilayer ceramics capacitor, the effects of acceptor dopant MnCO₃ on the microstructure, insulation resistivity (IR) and dielectric properties of BNST ceramics doped with 1 wt% BaCuB₂O₅ (BCB) sintered under a reducing atmosphere of moist N₂-1%H₂ were investigated. Results showed that MnCO₃ effectively rendered BNST-BCB ceramics resistant to reduction. Mn ions completely substituted into the Ti⁴⁺ site of BNST at <1.5 wt% MnCO₃ doping content, whereas secondary phases were formed with increased MnCO₃ addition. Resistivity as high as 10¹² Ω cm was effectively achieved in ceramics with the addition of >1.5 wt% MnCO₃, and the dielectric constant (ε _r ) of BNST-BCB was not obviously modified by the presence of additive. Moreover, 2 wt% MnCO₃-doped BNST-1wt% BCB ceramics sintered in a reducing atmosphere exhibited attractive properties with ε _r  = 75.1, tanδ = 0.00115, TCC = −42.3 ppm/°C and IR = 4.56×10¹² Ω cm.