Preparation And Properties Of Anti-reducing BaTiO₃-based Dielectric Ceramics For Wide Temperature Range Application

The rapid development of electronic industries required a larger capacity of multilayer ceramic capacitors（MLCCs）.Thin film and base metal internal electride（BME）are the development trends,and Co-sintering dielectric materials with BME in reducing atmosphere is an effective means to solve this problem.However,Ti ions are easily been reduced to cause the semiconducting of BaTiO₃ when sintered in reducing atmosphere.Meanwhile,the existence of sharp curie peak of BaTiO₃ is undesirable for dielectric temperature stability.In this paper,BaTiO₃-BiMeO₃ system with good dielectric temperature stability were selected to modified.The effect of different addition doping materials on the insulation properties of BaTiO₃ ceramics sintered in reducing atmosphere were investigated.（1-x）BaTiO₃-xBi(Zn_2/3Nb_1/3)O₃[（1-x）BT-xBZN]ceramics were prepared via solid state reaction method and sintered in air.The influence of BZN doping content on the phase structure,micromorphology,dielectric properties and ferroelectric properties were investigated.The results indicated that the dielectric temperature stability improved as the cost of decreased dielectric constant when doping content increased.The same system materials sintered in reducing atmosphere and semi-conducting samples were obtained.Doing acceptors Mn⁴⁺and Ca²⁺improved the insulation properties and dielectric temperature stability of（1-x）BT-xBZN ceramics.The resistivity of 1.0 wt%MnO₂ doped 0.925BT-0.075BZN reached3.5×10¹⁰Ω·cm.Dielectric properties ofε=1310 and tanδ=2.0%for 0.5 wt%MnO₂and 2 wt%Ca²⁺Co-doped 0.85BT-0.15BZN were achieved,and the temperature range of TCC≤±15%was-45 ^oC-178 ^oC.Variable-valence acceptor Co was doped into BaTiO₃-BiMeO₃,and a small amount of Mn was added to obtain 0.5 wt%MnO₂ doped（1-x）BaTiO₃-xBiCoO₃[abbreviated as（1-x）BT-xBC-M]ceramics.Then the（1-x）BT-xBC-M ceramics were sintered in air and reducing atmosphere,respectively.The phase structure,micromorphology,dielectric properties and insulating properties of（1-x）BT-xBC-M ceramics sintered in different atmospheres were investigated.It was found that（1-x）BT-xBC-M ceramics sintered in reducing atmosphere exhibited excellent insulating properties over 10¹³Ω·cm and maintained at a value than 10¹¹Ω·cm at 150^oC.In the temperature range of-55 ^oC-125 ^oC,TCC≤±22%,which met X7S specification.While the dielectric constant and dielectric loss become abnormal and the insulating properties were deteriorated for the same sample sintered in air.Hole-electron trapping effect and the defect dipole forming effect were revealed by XPS and TSDC test,which were responsible for the anti-reduction mechanism.The nominal composition（1-x）BaTiO₃-xBi(Zn_0.5Y_0.5)O_2.75[（1-x）BT-xBZY]ceramics were prepared.The effect of rare earth ions Y on the anti-reduction properties and dielectric temperature stability of（1-x）BT-xBZY ceramics were studied.As the doping amount increasing,the insulation resistivities increased from5.0×10⁸Ω·cm at x=0.05 to 6.1×10¹²Ω·cm at x=0.2 and then decreased to 7.2×10¹¹Ω·cm at x=0.25.The dielectric-temperature curve become flatten.When doping amount x=0.15,the optimum performances with resistivity over 10¹²Ω·cm,dielectric properties ofε=1362 and tanδ=1.4%were achieved,which met X8R specification for MLCC application.The XPS and TSDC results shown that the anti-reduction mechanism was attributed to the formation of the defect dipole[2Y_Ti’-V_O●●]and the reduction of Bi ions.