Co-alloying gives researchers greater control of piezoelectric material properties

To protect the health of humans processing them, industries that manufacture piezoelectrics—materials that generate an electric charge when subjected to mechanical stress and have wide-ranging applications in medical devices, consumer goods, and beyond—are considering as a possibility switching from dominant lead zirconate titanate (PZT) to a lead-free alternative called AlN. AlN-based piezoelectrics are also more stable than PZT in high temperature applications up to 1200 degrees Celsius.

AlN, however, has its own challenges. This lead-free material doesn’t have high enough piezoelectricity. Alloying AlN with yttrium nitride (YN) increases its piezoelectricity, but creates another problem: it softens AlN. And to use AlN in resonator applications, it must be stiff.

A group of engineers researched AlN challenges by exploring co-alloying AlN with YN and another nitride, boron nitride (BN). They found the combination achieves material stiffness and maintains the piezoelectricity of AlN. They report on their research in Journal of Applied Physics.

Using the VASP package, a computer program for atomic scale materials modeling, the engineers constructed computer models of alloys of AlN, YN, and BN, and then used density functional theory to determine their electronic structure. They then applied strain to the structures and measured their polarity to determine the computer models’ piezoelectricity. To assess mechanical stiffness, they changed the structures’ length in the simulation and measured the energy change.

Through this computational co-alloying, the researchers found that BN stiffens AlN without decreasing its piezoelectricity. Coauthor Cristian Ciobanu says the presence of shorter and stiffer B−N bonds provides the elastic stiffening of AlN-YN, allowing researchers to tune the properties of AlN with alloying. Ciobanu adds that next the researchers will create the AlN-Y-B-N alloys and, after validation, expects this system to be adopted by industry.

Source: “Tuning the piezoelectric and mechanical properties of the AlN system via alloying with YN and BN,” by Sukriti Manna, Geoff L. Brennecka, Vladan Stevanović, and Cristian V. Ciobanu, Journal of Applied Physics (2017). The article can be accessed at https://doi.org/10.1063/1.4993254 .