Papers by Keyword: X7R

Abstract: Dispersion plays an important role in aqueous chemical coating process for the preparation of BaTiO3 based next generation BME MLCC powder, since it affects coating coverage and layer morphology of the BaTiO3 particles as well as the microstructure and dielectric properties of the ceramics. In this paper, Poly (acrylic acid-co-maleic acid) (PAM) is used as dispersant, its content influences are carefully investigated. It is known that low content of dispersant leads to not only poor dispersion, low coverage and irregular coating layer of BaTiO3 particles, but also bad temperature coefficient of capacitances and inhomogeneous microstructure of the resultant BaTiO3 ceramics, while excessive dispersant deteriorates the microstructure and performance by reducing the density of ceramic. With proper dispersant content, the particles are dispersed and coated perfectly, finally the dense X7R-satisfied ceramic are obtained with average grain size 103nm and fine microstructure, meeting the requirement of next generation MLCCs.

Abstract: Li-Ti-O (abbreviated as LTO) nano-composites were synthesized via sol-gel process, and then doped BaTiO3 based X7R type ceramics. The LTO nano-composites and their ceramics were characterized by means of thermaogravimetric, Fourier-transform infrared, X-ray diffraction methods, transmission electron microscopy. We also characterized the dielectric properties of the LTO doped BaTiO3 based ceramics of X7R type. The results indicated that LTO nano-composites were nanometer scale powders. The pH value and calcining temperature had an influence on particle size of LTO sintering aids. At pH about 3 and with calcining at 600 °C, the nano-composites attained minimum particle size (about 10 nm). By adding 0.10 wt% of the LTO nano-composites, the temperature permittivity achieved about 4200 when sintered at 1240 °C for 4 h, and the dielectric properties met X7R standard.

Abstract: In this work, a sub-micron grained sized (<500nm) ceramic (> 92% of theoretical) has been obtained using nano-sized BaTiO3 powders synthesized through a high-gravity reactive precipitation (HGRP) process. Permittivity of the prepared ceramic is greater than 2500. Also, low change ratio of temperature in the range of −55°C~ 125°C
i.e.< ±15% renders the ceramic to meet the EIA X7R characteristics. In the ceramic compositions, Dy2O3, BaCO3, CaCO3, MnCO3 and MgO were used as dopants. After being mixed and dry-pressed, the above mentioned compositions in reducing atmosphere (N2 and 5% H2) were sintered at 1210°C−1290°C for 2h, respectively. Experimental results show that HGRP BaTiO3 powders have good dielectric properties. The dielectric properties as well as the microstructure of the ceramic are both sensitive to the change of sintering temperature.

Abstract: The barium titanate based X7R ceramics, which are doped with rare earth oxide, Nb2O5, Co3O4 and ZnO-B2O3, could be sintered at a rather low temperature to satisfy the X7R requirements with good permittivity and dielectric loss. In this paper, different doping methods of sintering aids have been used to prepare X7R BaTiO3 ceramics. Samples were sintered at a low temperature and the relationship of doping methods and sintering properties has been concluded.

Abstract: The effect of rare earth oxides (Y2O3 and Dy2O3) on the microstructure and electrical properties of the X7R-type ceramics for base metal internal electrode multilayer ceramic capacitor (BME-MLCC) was investigated. As the amount of Y increased, the dielectric constants and the dielectric losses increased, while the temperature coefficient of capacitors (TCC) curve rotated in counterclockwise direction. On the contrary, the dielectric constants decreased with Dy, and the TCC curve remained the same. The grain growth can be inhibited by the Dy2O3, concluded from XRD analysis. The different influences on dielectric properties between Y2O3 and Dy2O3 were discussed by defect chemistry. Y3+ acted as acceptor, performing B-site substitution, while Dy3+ showed the amphoteric behavior. By optimizing appropriate qualities of Y2O3 and Dy2O3, the most-compatible composition for BME X7R ceramics can be obtained.

Abstract: In this paper, Sr-doped BaTiO3 based X7R ceramic was prepared. This material has dielectric constant of about 2000, temperature coefficients of capacitance (TCC) at 125°C of 11%, insulation resistivity of 12 × 1012 Ω⋅cm and grain size of 350 nm. The effects of Sr doping on the properties of the ceramics were also investigated.