Title: Tuning the piezoelectric and mechanical properties of the AlN system via alloying with YN and BN,
Abstract: Recent advances in microelectromechanical systems often require
multifunctional materials, which are designed so as to optimize more than one
property. Using density functional theory calculations for alloyed nitride
systems, we illustrate how co-alloying a piezoelectric material (AlN) with
different nitrides helps tune both its piezoelectric and mechanical properties
simultaneously. Wurtzite AlN-YN alloys display increased piezoelectric response
with YN concentration, accompanied by mechanical softening along the
crystallographic c direction. Both effects increase the electromechanical
coupling coefficients relevant for transducers and actuators. Resonator
applications, however, require superior stiffness, thus leading to the need to
decouple the increased piezoelectric response from a softened lattice. We show
that co-alloying of AlN with YN and BN results in improved elastic properties
while retaining most of the piezoelectric enhancements from YN alloying. This
finding may lead to new avenues for tuning the design properties of
piezoelectrics through composition-property maps.
Keywords: piezoelectricity, electromechanical coupling, density functional
theory, co-alloying