Weizmann Institute of Science scientists have created a new ceramic material that may replace lead-based components in a large number of electronic devices - from cell phones to printers
"Too good to be true", this was the initial reaction in Prof. Igor Lubomirsky's research group at the Weizmann Institute of Science to the sight of the ceramic material they created in their laboratory. The new material belongs to a well-known family that is used in many technologies but creates a big environmental headache, since the materials that belong to it usually contain lead - one of the most toxic metals in our world. Amazingly, the material they created does not fall short in its performance of the materials used in the industry today, and this without having any toxic or polluting components.
The family in question is the family of piezoelectric or electrostrictive materials - materials that deform under the influence of an electric field. This distortion is exploited in countless electronic devices to create tiny motors. For example, in mobile phones, the tiny distortion caused by electrical voltage is used to start charging the battery or to move the camera lens and bring it into focus; In industrial printers, these materials are used for a measured and controlled release of ink.
The components made from these materials are often too small to be worth recycling, and thus tons of lead find their way into landfills. Lead-based applications have been phased out in developed countries, but these materials are still permitted for use due to their essentiality and the lack of suitable substitutes. To illustrate, the global market for piezoelectric materials is more than $20 billion per year and continues to grow.
Previous attempts by scientists around the world to produce lead-free materials for these uses were not fully successful: the materials they produced were either too chemically active or too complicated to manufacture. In contrast, the new material produced in the laboratories of the Weizmann Institute of Science - cerium oxide plus about ten percent zirconium oxide - does not tend to produce chemical reactions with its environment and is easy to produce. Moreover, its greatest advantage may be energy efficiency: it consumes less energy than existing materials to do the same work. If all this is not enough, its source materials are also cheap and readily available: both cerium and zirconium are quite common in the earth's crust and are already produced in mines around the world for various industrial uses. Cerium oxide in powder form is used, for example, to polish lenses and in catalytic converters - devices to reduce vehicle emissions.
Thanks to all this, the new ceramic material may be a successful and environmentally friendly alternative to these materials, but when the research started more than a decade ago, Prof. Lubomirski never dreamed of any industrial applications. His research group discovered at the time that under certain conditions, cerium oxide does not behave as expected: the scientists detected in this oxide an electrostrictive effect a hundred times greater than predicted by theory. Although it was a tiny and obviously impractical effect, the discovery was surprising, and the group continued to investigate it.
Then about three years ago, Maxim Vernik, a doctoral student in Prof. Lubomirsky's group, performed an experiment that produced shocking results. In a series of experiments he combined trivalent atoms in cerium oxide, meaning atoms with three electrons in their outer shell. When he exposed the materials to an electric field, an interesting phenomenon was discovered that has clear laws: the smaller the inserted atoms were, the more the material deformed. In light of the findings, Wernicke was curious to see what would happen if he introduced as small atoms into the oxide as possible, but eventually he ran out of trivalent atoms that could be combined with cerium. So he decided to try and insert zirconium oxide atoms instead, even though they have four electrons in the outer shell and not three. The result amazed him and the rest of the group: the deformation in the material created did not climb as high as in the previous series of experiments - it jumped 200 times.
"For about a decade we studied a phenomenon that was considered completely useless, we did it purely out of scientific curiosity," says Prof. Lubomirski. "And here the curiosity gave birth to a material with performance that does not fall short of the best materials currently used in the industry."
Along with understanding the properties of the new material in the context of possible applications, the researchers continue to try to understand why cerium oxide does not behave according to theory. "This is an animal we have never met in our zoo," says Prof. Lubomirski.
Since the unusual phenomenon was discovered for the first time, Prof. Lubomirski's group has been investigating it in collaboration with Prof. Anatoly Frankel from Stony Brook University, one of the world's leading experts in EXAFS spectroscopy. Recently Prof. Yue Kee from Brown University also joined the team, but the task is still far from perfect. Prof. Lubomirski says: "We still do not fully understand the phenomenon, but this is exactly what makes the research interesting."
The study was led by Wernick together with Dr. Boyuan Shaw from Brown University. The authors of the article also include Juneying Lee, Elad Geber, Dr. Alan Wechtel, Dr. David Ahara and Sergey Khodorov from the Institute's Department of Molecular Chemistry and Materials Science; and Dr. Praheld Roth from Stony Brook University.
#Science_Numbers
- Lead is the 2nd most toxic metal in our world, after arsenic.
- Lead in the blood is dangerous to health at any dose, but levels of 3.5 micrograms per tenth of a liter of blood in children require immediate medical attention.
- According to data from the American Centers for Disease Control and Prevention (CDC), these levels of lead in the blood and even higher characterize 2.5% of infants aged 1 to 5 in the United States.
