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Piezo Glass Ceramic

Piezo-electric glass ceramics (left) are free from lead and stabile in temperature up to 600°C. SCHOTT researchers paved the way to product development of the unique new material by using special lab castings (right).
(Photos: A. Stephan)

Heribert Herrgen

A Material Generates Voltage and Movement

For the first time ever, researchers have succeeded in carrying over piezo-electric glass ceramics from the laboratory into product development. These lead-free materials offer completely new qualities.

Piezo-electric materials are capable of transforming mechanical energy into electrical energy and vice versa. They expand quickly and precisely when connected to voltage. This effect has been leveraged in manufacturing of semiconductors for quite some time. With nanopositioning of components, movements of one-millionth of a millimeter are at stake.

Piezo-electric materials are also used as sensors that measure changes in pressure and oscillation. Typical areas of application include medical technology, diagnostic ultrasound, for example, and construction of vehicle engines. Piezo-driven injection valves in diesel engines achieve much shorter manipulating times than traditional magnetic valves, reduce consumption and enhance running smoothness and the quality of exhaust gas. Used as sensors, elements made of piezo-electric material also enhance safety systems in vehicles, such as airbags or clearance indicators.

The piezo effect of natural monocrystalline materials, such as quartz or tourmaline, is extremely low. Better performance results were obtained with polycrystalline ferroelectrical ceramics, such as barium-titanate and lead-titanate-zirconate (PZT). PZT piezo ceramics are available in good supply and today represent the most commonly used ceramics for sensor applications and actuators capable of moving in a quick and precise manner. Lead is always an essential component; however, it is harmful to both the environment and health.
The piezo technique is used particularly in building engines. Such piezo inline injectors enable diesel fuel-injection systems to reduce fuel consumption, emissions and the intensity of running noises.
(Photo: Bosch)

Until now, ceramic manufacturers were only in a position to use lead-free alternatives to a very limited degree. And despite their numerous areas of application, PZT ceramics leave a lot to be desired with respect to temperature stability, performance and durability. Piezo-electric glass ceramic, a newly-developed material, offers precisely these types of advantages. ”We combine the piezo-electric characteristics of lead-free crystals with SCHOTT glass and glass ceramic manufacturing technologies, particularly with respect to the numerous molding possibilities,” explains SCHOTT researcher, Dr. Ina Mitra. In fact, SCHOTT has already developed glass ceramics that exhibit some better piezo-electric traits than existing materials, yet are free from lead. This is a major advantage, because it enables the European RoHS (Restriction on Hazardous Substances), the current regulations on the reduction of contents harmful to one’s health, to be met during manufacturing, usage and disposal of these materials.

Furthermore, some varieties of the new material are transparent and capable of unfolding their piezo-electric characteristics at temperatures of up to 600° C. ”This will open up new opportunities for this innovative material in the near future, in high temperature areas or wherever only expensive mono-crystals have been put to use, for example,” explains Dr. Ina Mitra.
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