Piezoelectric materials are materials that produce an electric current when they are placed under mechanical stress. Usually, they rely on their crystal structure alone to create an electrical charge. This makes the materials attractive for a variety of sensing applications. Such miniaturized devices with electrical and mechanical properties are called micro-electro-mechanical systems (MEMS).
Scientists at EPFL have found a new mechanism of harnessing piezoelectricity by manipulating atomic defects in a lead-free material that is normally not piezoelectric. They have created a gadolinium-doped cerium oxide compound, a promising alternative to certain piezoelectric materials. It’s also lead-free, unlike the best piezoelectric materials, which means that it could be employed in bio-compatible medical applications.
This study was carried out under the BioWings project, an EU initiative to develop lead-free MEMS used as actuators in various biomedical applications. BioWings wants to create systems based on electrostriction property instead of piezoelectricity.
Electrostriction involves converting electrical energy into mechanical energy. It slightly occurs in all materials, however, the effect is very small. The significant difference between piezoelectricity and electrostriction is that piezoelectric materials expand or contract depending on the applied electrical field. In contrast, electrostrictive materials deform the same way regardless of the orientation of the electric field.
Applying a consistent electric field with an alternating field could break the symmetrical electrostrictive effect. Doing so converted the electrostrictive property of gadolinium-doped cerium oxide into a piezoelectric one.
Dr. Dae-Sung Park, a postdoc at EPFL’s research group for ferroelectrics and functional oxides, said, “The addition of gadolinium in ceria creates a large concentration of atomic defects (oxygen vacancies) that are mobile in the presence of an electric field. That means that a strong piezoelectric effect in gadolinium-doped cerium oxide can be induced by controlling the defects.”
Damjanovic adds, “By manipulating the mobile defects, we can increase piezoelectric susceptibility by a factor of 100 relatives to even the most powerful lead-containing piezoelectric materials. Our goal is not to eliminate or replace these materials, but rather to provide alternatives to those containing lead.”
This is a significant scientific discovery for ionic, piezoelectric, and ferroelectric fields.
- D. S. Park et al. Induced giant piezoelectricity in centrosymmetric oxides. DOI: 10.1126/science.abm7497