The Preparation And Study On High-performance BaTiO₃-based Dielectric Materials Sintered In A Reducing Atmosphere

The rapid development of 5G communications and new energy vehicles is increasingly demanding low-cost,large-capacity and high-reliability multilayer ceramic capacitors（MLCC）.The substantial cost saving and dielectric performance improvement can be achieved by utilizing base metal（Ni）as the internal electrode of MLCC instead of traditional noble metal（Ag-Pd）.However,Ni-MLCC needs to be prepared in a reducing atmosphere,and based on this,the dielectric materials with non-reducible and high dielectric properties are needed.Therefore,it has become an urgent research topic to develop non-reducible dielectric materials with excellent comprehensive dielectric properties（high dielectric constant,low dielectric loss,high insulation resistivity and good temperature stability）in a reducing atmosphere.Barium titanate（BaTiO₃）is widely used in MLCC dielectric materials due to its higher dielectric constant and low loss.However,due to the influence of the reducing atmosphere,the valence of Ti⁴⁺in pure BaTiO₃ can be easily reduced to Ti³⁺,and a large number of free electrons and oxygen vacancies are generated,resulting in semi-conduction and deterioration of insulation.Thus,this article first study the influence mechanism of sintering atmosphere on BaTiO₃.Based on this,donor-acceptor dopants and broadening dopant are introduced to improve the dielectric properties and temperature properties.Further,variable valence ion is introduced to enhance the dielectric constant of the BaTiO₃ system,and comprehensively optimize the dielectric properties.The main work of this paper is as follows:（1）Research on the influence mechanism of sintering atmosphere on the structure and properties of BaTiO₃.The BaTiO₃ dielectric materials sintered in different atmospheres are deem to research objects.The interaction between the internal defect structure and dielectric properties of the BaTiO₃ crystal is analyzed by the microscopic characterization and first-principles calculation method.The results show that the free electrons,oxygen vacancy and crystal structure distortion in BaTiO₃ crystal are the underlying physical mechanisms leading to the increase of dielectric loss and deterioration of insulation properties in a reducing atmosphere.Therefore,the inhibition of free electrons and oxygen vacancy is the key to improve the dielectric properties of BaTiO₃-based dielectric materials.（2）Research on donor-acceptor co-doping modification mechanism under reducing atmosphere.Based on the above research,Bi³⁺,Mg²⁺and Zr⁴⁺are co-doped in BaTiO₃ to adjust the dielectric properties and temperature stability in a reducing atmosphere.The change of charge carriers with different content of(Bi³⁺,Mg²⁺,Zr⁴⁺)is analyzed,and the influence mechanism of defect dipoles on carrier distribution is proposed.Besides,the relationship between the internal polarization mechanism and dielectric properties of this system is established.Based on this,the BaTiO₃-based dielectric material with good dielectric properties is obtained:ε_r=2020,tanδ=1.59%,ρ_v>1.0×10¹¹Ω·cm and the temperature stability meets EIA X8R standard.（3）Research on the comprehensive regulation mechanism of high dielectric constant,low loss and temperature stability.The variable valence ion Mn⁴⁺is adopted to further improve the dielectric constant and comprehensively optimize the dielectric properties of BaTiO₃-based dielectric material.The influence of dielectric properties with different contents of Mn O₂ is explored.Then,the interaction models among crystal structure,defect structure and polarization mechanism are established.Finally,the BaTiO₃-based dielectric material with high dielectric constant,low dielectric loss,high insulation resistivity and good temperature stability is prepared:ε_r=3643,tanδ=1.10%,ρ_v>1.0×10¹¹Ω·cm,meeting the EIA X8R standard.