IntroductionIn recent years, the high-voltage and high-power multi-layer ceramic capacitors (MLCCs) have attracted extensive attention with the development of new energy vehicles, 5G communication and high-power pulse technologies. At present, the materials used in the MLCC inner electrode are mainly precious metal (Ag/Pd or Au) and base metal (Ni or Cu). Base metal materials have more cost advantages compared with the precious metal materials. In order to prevent the oxidation of the base metal Ni or Cu at high temperatures, it is necessary to sintering in a low oxygen or reducing atmosphere. In order to obtain MLCC products with excellent performance, it is necessary to strictly control the matching of the sintering atmosphere between the inner electrode and the ceramic body during the sintering process. The crystal structure and electrical properties of the ceramic will be significantly reduced in the reducing atmosphere or low oxygen atmosphere environment, mainly because the precipitation of metal lead will destroy the lattice structure, or produce lattice defects. Therefore, it is of great significance to study the properties of PbLaZrSnTiO₃-based (PLZST-based) antiferroelectric ceramics in low oxygen sintering atmosphere. In this paper, PLZST-based antiferroelectric ceramics were sintered in four kinds of low oxygen sintering atmosphere. The crystal structure, microstructure and electrical properties of PLZST-based antiferroelectric ceramics were studied. Moreover, the energy storage properties of all samples were studied.MethodsPb_0.95La_0.02Sr_0.02(Zr_0.50Sn_0.40Ti_0.10)O₃ (PLSZST) antiferroelectric ceramics doped with were prepared using the traditional solid-state method. High quality raw materials, namely Pb₃O₄(95%, Sinopharm), La₂O₃(99.99%, Acros), ZrO₂(99%, Aladdin), SnO₂(99.8%, Sinopharm), TiO₂ (99.8%, Sinopharm) and SrCO₃(99%, Sinopharm), were weighted 500 g according to stoichiometric and ball milling for 12 h with ethyl alcohol as a solvent and dried at 70 ℃. These raw materials were calcined at 850 ℃ for 2 h in a closed crucible. Then, 0.6% BaCO₃-B₂O₃-SiO₂-K₂CO₃(BBSK, in mass) was added to the mixed powder according to the solid weight ratio as the calcination powder. After ball milling for 12 h, the powder was dried. Next, the powder was pressed into pellets at 20 MPa with 5% Polyvinyl Alcohol (PVA, in mass) as the binding agent 2 mm thick and 10 mm in diameter. Finally, the green ceramics with BBSK addition were sintered at 1020 ℃ and low oxygen sintering atmosphere (5.3×10^–10, 2.1×10^–9, 2.1×10^–8, 1.3×10^–7 atm) and air for 2 h in closed crucibles filled with the calcination powder.Results and discussionIn order to study the effect of sintering atmosphere on the crystal structure of PLSZST-0.6% BBSK (in mass) antiferroelectric material, XRD were conducted as shown in Fig. 1. It can be seen that all samples have perovskite structure, and a small amount of second phase is generated, which may be pyrocholate phase produced by Pb volatilization at high temperature. From the splitting peak near 44.2°, it can be seen that the intensity and Angle of the two splitting peaks do not change under the condition of low oxygen atmosphere, which indicates that the tetragonal structure of the ceramic body does not change. The peaks of (200) and (002) move to the lower Angle at lower oxygen content, indicating that the low oxygen atmosphere leads to the lattice distortion of the material. Then, the microstructure was studied. As can be seen in the surface micrograph, there are no metal lead or other substances precipitated from the ceramic body as observed in those samples treated at low oxygen sintering atmosphere. It can be seen from the f dielectric temperature spectra that all samples show the same variation characteristics. With the increase of temperature, the dielectric constant first increases to the maximum value and then slowly decreases. This dielectric anomaly peak is caused by the transformation of tetragonal antiferroelectric phase into paraelectric phase. With the increase of frequency, the dielectric constant and the peak value of dielectric anomaly do not change significantly, which indicates that the ceramics are a diffuse phase transition, and does not change with the change of oxygen content, which indicates that the oxygen content does not change the phase transition characteristics of antiferroelectric. With the decrease of oxygen content, the breakdown field strength and maximum polarization strength of the ceramic decrease, resulting in the gradual decrease of the saturated energy storage density and recoverable energy storage density of the ceramic body. The ceramic sintered at 5.3×10^–10 atm has a recoverable energy storage density of 2.76 J·cm^–3 which is lower than that of the ceramic sintered at air (3.56 J·cm^–3), showing a discharge energy density of 2.21 J·cm^–3.ConclusionsMulti-layer ceramic capacitors with base metal inner electrodes have been widely concerned because of its lower cost advantages. In order to prevent the oxidation of the base metal inner electrodes (Ni or Cu) at high temperatures, it needs to be sintered in low oxygen or reducing atmosphere. The effect of low oxygen atmosphere on the electrical properties of PLSZST antiferroelectric ceramics was studied. With the decrease of oxygen content, the insulation characteristics and energy storage characteristics of antiferroelectric ceramics were reduced. Under the oxygen content of 5.3×10^–10 atm, the ceramic has a recoverable energy storage density of 2.76 J·cm^–3, which is lower than that of sintered sample under air (3.56 J·cm^–3), has a discharge energy storage density of 2.21 J·cm^–3, and has a discharge current of 28.6 A. This work provides understanding of anti-reduction characteristics of PLZST-based antiferroelectric ceramics, and further promotes the development and production of PLZST-based antiferroelectric multilayer ceramic capacitors with internal electrodes in base metals.