(742h) Understanding and Improving the (Al,Sc)N Heterostructural Alloy through DFT Calculations and Combinatorial Synthesis

Authors: 
Millican, S. L., University of Colorado Boulder
Talley, K., Colorado School of Mines
Weimer, A. W., University of Colorado Boulder
Zakutayev, A., National Renewable Energy Laboratory
Musgrave, C. B., University of Colorado Boulder
Brennecka, G., Colorado School of Mines
Holder, A. M., University of Colorado at Boulder
The tailoring of materials properties by alloying is routinely utilized to design materials for targeted technological applications. Despite the great successes of alloying in isostructural systems, heterostructural alloying remains a fundamentally unexplored area. In heterostructural alloys, the crossover between different crystal structures enables the control of the atomic structure by variation of the composition. The deliberate manipulation of local atomic coordination symmetry introduces an additional materials design parameter for tuning the piezoelectric response of a material. Aluminum nitride (AlN) is an important piezoelectric material for applications such as bandpass filter resonator devices for wireless communication; however, AlN has a relatively low piezoelectric response and improved piezoelectric materials are required to more efficiently utilize the electromagnetic spectrum and increase device battery life.

In this talk, we present a complementary theoretical and experimental investigation of piezoelectrically active nitride alloys to develop design principles and approaches for utilizing heterostructural alloying as a materials design strategy. We use ab initio methods to predict the structural and electronic properties of Al1-xScxN and Al1-x-y­ScxByN heterostructural alloys for the energetically competitive polymorphs and compute their corresponding equilibrium phase diagrams and materials properties. Combinatorial sputtering is employed as a non-equilibrium growth technique to overcome thermodynamic solubility limits and produce metastable thin-film samples spanning the alloy composition range. The effect of incorporation of scandium and boron into the AlN on properties including crystal structure, film texture, and piezoelectric properties is explored.

The experimentally validated predictions, theory guided combinatorial synthesis, and characterization of piezoelectric heterostructural alloys exemplify how our integrated research strategy is used to design and realize functional metastable materials. Our approach establishes a new route for the control of structure-property and composition-structure relationships by accessing non-equilibrium phase space to develop new piezoelectric materials with uniquely tailored properties for specific applications.