| Ceramic capacitors are widely used in the field of electronic components because of their excellent performance.With the application of ceramic capacitors under some harsh working conditions,higher requirements are placed on the dielectric materials of ceramic capacitors,that is,high dielectric constant and low dielectric loss in a wide temperature range.Barium titanate(BaTiO3)has become the best candidate material for Y series capacitors because of its large dielectric constant at Curie temperature.In addition,multilayer ceramic capacitors(MLCC)are difficult to prepare by using base metal as the inner electrode and co-firing with the electrode in a reducing atmosphere due to its unique co-firing process of the dielectric layer and the inner electrode.In this paper,the electrical properties and Curie temperature regulation of rare earth element doped(Ba0.95Ca0.05)(Zr0.19Ti0.81)O3(BCZT)ceramics were studied,and the low temperature sintering process of ceramics was studied,which provided technical support for the preparation of MLCC with low temperature co-firing of Ni electrode.The main work of this paper is as follows:(1)(Ba0.95Ca0.05)(Zr0.19Ti0.81)O3(BCZT)ceramics with different Y3+ doping positions at A,B and A/B site were prepared by traditional solid-state reaction method.The effects of different Y3+ doping positions on the phase structure,microstructure,dielectric properties and electrical conductivity of the ceramics were studied.Y3+ can be successfully incorporated into the BCZT lattice,The shift of(200)peak proves that Y3+ successfully enters the designed vacancy.The Asite doping has little effect on the grain size and Curie temperature,while the B-site doping causes the grain size and Curie temperature to decrease with the increase of doping concentration.For the A/B-site doped samples,the grain size and Curie temperature are related to the doping concentration.The sample doped with 1.5 mol%Y3+ at the A site obtained a dielectric constant of 17443 and a low dielectric loss of 0.014 at room temperature.In the range of-30～85℃,the change rate of dielectric constant is between-82%and+22%.(2)The regulation mechanism of Curie temperature is discussed from the aspects of average size effect(<R>),variance effect(σ2),local electric field and tolerance factor(t)theory.The dominant factors of Curie temperature regulation are different at different doping positions.When A-site doping,the σ2 effect is the dominant factor,and when B-site doping,the<R>effect is the dominant factor.The increased σ2 makes Curie temperature stable,and the increased value makes Curie temperature decrease rapidly.Whether the tolerance factor t matches the valence also has a significant effect on the Curie temperature.(3)Y3+B-site doped ceramics doped with ZnO-B2O3 were prepared by traditional solid-state reaction method.Ag electrodes were plated in air atmosphere and Ni electrodes were plated in reducing atmosphere.The effects of different sintering additive contents and different atmosphere treatments on the phase structure,microstructure,dielectric properties and conductivity were studied.The sintering aids and reducing atmosphere will not change its phase structure.The introduction of sintering aids successfully reduced the sintering temperature of the ceramics from 1475℃ to 1250℃.ZnO-B2O3 belongs to the B-site acceptor substitution to introduce oxygen vacancies,and the carrier migration rate is accelerated at high temperature,which increases the conductivity.In the reducing atmosphere,the relative density of the ceramics becomes worse,the acceptor doping of Y3+reduces the electron concentration,Zr4+ increases the binding of oxygen vacancies,reduces the overflow of oxygen vacancies in the lattice,increases the dielectric constant,and shows a certain anti-reduction.The optimum composition successfully obtained a large dielectric constant of 8695,a low dielectric loss of 0.023 and a resistivity of 9.2×107 Ω·m at room temperature.In the range of-30℃ to 85℃,the change rate of dielectric constant is between-82%and+22%.This work provides a theoretical basis for improving the dielectric properties and Curie temperature regulation of BaTiO3-based ceramics,and provides technical support for the preparation of BaTiO3/Ni internal electrode co-fired multilayer ceramic capacitors(MLCC). |
