Implications of Heterostructural Alloying for Enhanced Piezoelectric Performance of (Al,Sc)N

Kevin R. Talley, Samantha L. Millican, John Mangum, Sebastian Siol, Charles B. Musgrave, Brian Gorman, Aaron M. Holder, Andriy Zakutayev, Geoff L. Brennecka

Research output: Contribution to journalArticlepeer-review

56 Scopus Citations

Abstract

An understanding of the heterostructural implications on alloying in the aluminum nitride-scandium nitride system (Al1-xScxN) can highlight opportunities and design principles for enhancing desired material properties by leveraging nonequilibrium states. The fundamental thermodynamics, and therefore composition- and structure-dependent mechanisms, underlying property evolution in this system have not been fully described, despite significant recent efforts driven by interest in enhanced piezoelectric performance. Practical realization of these enhanced properties, however, is hindered by the strong driving thermodynamic driving force for phase separation in the system, highlighting the need for increased study into the role of heterostructural alloying on the thermodynamics and composition-structure-property relationships in this system. With this need in mind, ab initio computed alloy thermodynamics and properties are compared to combinatorial thin-film synthesis and characterization to develop a more complete picture of the structure and property evolution across the Al1-xScxN composition space. The combination of structural frustration and a flattened free-energy landscape lead to substantial increases in electromechanical response. The energy scale of alloy metastability is found to be much larger than previously reported, helping to explain difficulties in achieving homogeneous materials with high scandium concentration. Scandium substitution for aluminum softens the wurtzite crystal lattice, and energetic proximity to the competing hexagonal boron-nitride structure enhances the piezoelectric stress coefficient. Overall, this work provides insight into the understanding of the structure-processing-property relationships in the Al1-xScxN system, suggests material design strategies for even greater property enhancements, and demonstrates the increased property tunability and underexplored nature of nonequilibrium heterostructural alloys.

Original languageAmerican English
Article number063802
Number of pages11
JournalPhysical Review Materials
Volume2
Issue number6
DOIs
StatePublished - 29 Jun 2018

Bibliographical note

Publisher Copyright:
© 2018 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.

NREL Publication Number

  • NREL/JA-5K00-71970

Keywords

  • dielectric properties
  • elastic modulus
  • phase diagrams
  • piezoelectricity
  • spinodal decomposition

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