The ceramics produced in the lab of Prof. Igor Lubomirsky at the Weizmann Institute of Science seemed too good to be true. They belong to a class of materials that form the backbone of many essential technologies, but unfortunately also pose an environmental problem because they usually contain lead, which is highly toxic.

The surprising thing about the Weizmann ceramic was that it performed as well as other materials in this category, while being completely non-toxic. The research was published in the journal Nature communication.

The new material falls into a class of substances that deform when exposed to an electric field, undergoing stresses and strains that are widely used in a variety of devices to produce small, precise movements.

In mobile phones, for example, the slight deformation caused by voltage can start the charging process or move the lens to create autofocus. In industrial inkjet printers, a plate flexes when voltage is applied, ejecting a controlled amount of ink.

Currently, materials that undergo such deformations (known as electrostrictors or piezoelectric materials, depending on the underlying mechanism) are a major source of lead pollution. Because electrostrictive and piezoelectric components are often too small to recycle, tons of lead regularly end up in landfills.

Although lead has been phased out of most other applications in the Western world, these materials are so indispensable that their use is still permitted. Piezoelectric materials, for example, represent an annual global market of over $20 billion.

Previous attempts by scientists around the world to produce lead-free electrostrictive or piezoelectric materials have met with only marginal success: some are too chemically reactive, others too difficult to make. In contrast, the Weizmann substance—cerium oxide mixed with about 10% zirconium oxide—is inert and easy to produce.

But perhaps the biggest potential advantage is that, compared to materials currently in use, it can produce the same deformation at a much lower dielectric constant. That means it stores less electrical charge. That means it takes less energy to do the same work.

In addition, the source materials for the new ceramics are cheap and readily available. Both cerium and zirconium are relatively abundant in the Earth’s crust and are mined around the planet for various industrial applications. Cerium oxide, for example, is often used in powder form to polish lenses and as a catalyst in catalytic converters, devices that reduce harmful emissions in cars.

Weizmann ceramics could therefore offer an attractive and environmentally friendly alternative to existing electrostrictive or piezoelectric materials. But when Lubomirsky first began the research that would lead to their discovery more than a decade ago, practical applications were far from his mind.

His team had discovered that under certain conditions the mechanical properties of cerium oxide, in its pure form and mixed with impurities, did not fit the classical picture. The electrostrictive effect was about 100 times stronger than expected according to the prevailing theory, still too small to be useful in practice, but intriguing. The team continued to investigate.

About three years ago, Maxim Varenik, a Ph.D. student in Lubomirsky’s lab, performed an experiment that yielded surprising results. He introduced trivalent impurities—atoms with a chemical valence of three, that is, with three electrons in their outer orbits—into cerium. When he applied voltage to the resulting substances, he noticed an interesting, regular phenomenon: the smaller the inserted atoms, the greater the electrostriction.

Because the increase in electrostriction had been in such a neat, straight line, he was curious to continue experimenting with smaller and smaller atoms. Eventually, however, he ran out of trivalent impurities; none of the smaller ones he had tried could be dissolved in cerium oxide.

Varenik then decided to introduce zirconium, the substance normally used in catalysts, even though it has four electrons in its outer orbit instead of three. To his surprise and everyone else’s, the electrostriction of the material he created did not jump up a notch, as had happened with the other experimental materials. Instead, it shot up about 200 times.

“For about 10 years we were studying something that was considered completely useless — we were doing it out of scientific curiosity,” Lubomirsky says. “Now we suddenly have a material with potential engineering applications. The stresses and strains produced in it by tension are comparable to the best commercial materials.”

In addition to investigating the properties that might make their ceramics attractive for industrial use, scientists in Lubomirsky’s lab are trying to explain why the electrostrictive performance was so far off the classical charts. “This is not an animal we’ve ever seen in our zoo,” Lubomirsky says.

Since discovering this nonclassical electrostriction, Lubomirsky’s team has been studying it in collaboration with Prof. Anatoly Frenkel of Stony Brook University, one of the world’s leading experts in a type of spectroscopy known as EXAFS. They were recently joined in this research by theoretician Prof. Yue Qi of Brown University.

Their task, however, is far from over. “We still don’t fully understand what’s happening in this material,” says Lubomirsky, “but that’s what makes it interesting.”