Use of an AC rather than a DC electric field can improve the piezoelectric response of a crystal. Now, an international team of researchers say that cycles of AC fields also make the internal crystal domains in some materials bigger and the crystal transparent.

“There have been reports that the use of AC fields could significantly improve the piezoelectric responses—for example by 20% to 40%—over DC fields and the improvements have always been attributed to the smaller internal ferroelectric domain sizes that resulted from the cycles of AC fields,” said Long-Qing Chen, Hamer Professor of Materials Science and Engineering, professor of engineering science and mechanics, and professor of mathematics at Penn State. “About three years ago, Dr. Fei Li, then a research associate at the Materials Research Institute at Penn State, largely confirmed the improvement of piezoelectric performances from application of AC fields. However, it was not clear at all how the internal ferroelectric domains evolved during AC cycles.

”Our group does mostly computer modeling, and more than a year ago we started looking into what happens to the internal domain structures if we apply AC fields to a ferroelectric piezoelectric crystal. We are very curious about how the domain structures evolve during AC cycles. Our computer simulations and theoretical calculations did show an improved piezoelectric response, but our simulations also demonstrated that the ferroelectric domain sizes actually got bigger during AC cycles rather than smaller as reported in the literature.”