17. März 2020, 13:01 Uhr | Ralf Higgelke
The dense microstructure of barium titanate as seen under a microscope.
Some three trillion ceramic capacitors are produced each year, and about 90 percent of them contain barium titanate. Researchers at Penn State have now sintered this material at extremely low temperatures. This not only saves energy, but also has other advantages.
Each mobile phone contains about a thousand components made of barium titanate. This is the basic compound used to manufacture high permittivity dielectric materials in multilayer ceramic capacitors (MLCCs).
A team of Penn State University researchers led by Clive Randall, professor of materials science and engineering, used a cold sintering process to densify barium titanate at less than +300 °C (572 °F). This is the lowest processing temperature ever reported. At the same time, the quality achieved in today's commercial manufacturing process at higher temperatures was maintained, the researchers said.
Sintering is a commonly used process to compress fine powders into a solid mass using temperature and pressure. This new cold sintering process achieves this at much lower temperatures and in less time than conventional sintering. According to the researchers, this could reduce both costs and environmental impacts of manufacturing a wide range of materials.
“Our work is the first example showing we can densify ferroelectric oxides in a single step,” said Kosuke Tsuji, a doctoral candidate in the Department of Materials Science and Engineering at Penn State and lead author of the study. “It should open up the possibility to densify many more inorganic materials at low temperatures.” It is the first time researchers have densified barium titanate in a single step using cold sintering. Previous attempts required secondary heating to produce materials with useful dielectric properties, said the scientists.
Sintering in Just One Step
The researchers used new chemistries to densify barium titanate in a single step. Cold sintering involves adding a few drops of liquid to ceramic powder. Reactions between moisture, heat and pressure create denser materials compared to heating at higher temperatures without liquid.
Previous cold sintering research used neutral or acidic solutions, but the new study incorporated hydroxide, an alkaline material. The hydroxide helped produce barium titanate with the necessary dielectric properties at lower temperatures, the scientists said.
“This research shows that materials that were previously difficult to sinter can now be done,” said Clive Randall, professor of materials science and engineering at Penn State, who led the development of cold sintering. “It takes us to the dream that we can eventually find the right chemistry to allow all ceramic materials, and maybe even metal materials, to be cold sintered.”
Lowering temperatures used in commercial manufacturing would not only be more energy efficient but could open the door to using less expensive metals and incorporating polymer composites into these capacitors, according to the researchers.
Kosuke Tsuji, et al., Single step densification of high permittivity BaTiO3 ceramics at 300 °C, Journal of the European Ceramic Society, Volume 40, Issue 4, 2020, DOI: https://doi.org/10.1016/j.jeurceramsoc.2019.12.022.