In this study, the high stability temperature coefficient of capacitance (TCC) characteristics of (Ba,Ca)(Ti,Zr)O 3 -based multilayer ceramic capacitors (MLCCs) were investigated using a novel sintering approach that combines rapid heating and constrained sintering. The novel sintering approach is based on a sandwich structure that the constrained (Ba,Ca)(Ti,Zr)O 3 -based MLCCs are covered with BaTiO 3 as a constraining layer on both sides. An in-plane tensile stress resulting from the mismatch between the constraining layer and the constrained layer during heating can effectively inhibit grain growth of (Ba,Ca)(Ti,Zr)O 3based MLCCs and then modify the TCC characteristics of (Ba,Ca)(Ti,Zr)O 3 -based MLCCs from Y5V (À82%≦△C/C≦ + 22% from À30°C to 85°C) to X5R (À15%≦△C/C≦ + 15% from À55°C to 85°C). The high continuity (>95%) of inner electrode and the fine grain size (0.56 lm) of BCTZ-based MLCCs with a non-core-shell structure can be attained by means of the rapid constrained sintering technique. The lifetime of the fine-grain-BCTZ-based MLCC fired by the novel sintering is superior to that of the coarse-grain-BCTZ-based MLCC fired by conventional sintering in a highly accelerated life test. *
In this study, the sintering temperature of a (Ba,Ca)(Ti,Zr)O 3 (BCTZ) dielectric for cofiring with a Cu inner electrode is determined to be lower than 1050 °C in a reducing atmosphere (N 2 /H 2 = 95/5) by using the sintering aids SiO 2 and Li 2 CO 3 . The contents of SiO 2 and Li 2 CO 3 are studied to achieve optimum dielectric characteristics and microstructure. The BCTZ dielectric with 0.25 wt % SiO 2 and Li 2 CO 3 fired with a Cu electrode at 1050 °C for 2 h in a reducing atmosphere shows promising properties, such as a dielectric constant of up to 9500, a low dielectric loss of 23 ' 10 %4 , and a high insulation resistance of up to 1.2 ' 10 12 Ω. However, the excess amount of Li 2 CO 3 results from the formation of the secondary phase. It has been determined that the secondary phase is (Ba 1.55 Ca 0.45 SiO 4 ) by high-resolution transmission electron microscopy and energy-dispersive spectrometry (HRTEM-EDS). The presence of the secondary phase is harmful to the properties of the BCTZ dielectric including dielectric constant, insulation resistance, and degree of dielectric loss. The interdiffusion of the dielectric-electrode interface is observed in the backscattered electron imaging (BEI) and line scan modes. The result indicates that such interdiffusion is easier from the electrode to the dielectric layer than from the dielectric layer to the electrode.
The residual stress built up by sintering causes not only the destruction of the structure of magnetic components but also a reduction in their permeability. In this paper, the relationship between residual stress and permeability is examined, and two possible methods for improving this situation are presented. Because one of the causes of increased residual stress is competition between the shrinking behaviors from the silver and ceramic layers inside the components during sintering, the first method is changing the particle size of the silver paste to alter its shrinking behavior. The results show that choosing a finer silver particle paste as the inner electrode material can reduce the onset temperature of shrinkage of the silver layer and then separate the silver layer from the ceramic layer to shrink the layers individually, reducing the residual stress. The second method is based on the phenomenon of separate shrinking seen in the first method, and we used carbon paste as the isolation layer for the silver and ceramic layers to achieve this. The results show that this method can reduce the residual stress more than the first one, although it can cause a high direct current resistance (DCR) and a low bending strength, and other conditions should be considered in order to avoid these weaknesses.
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