Local distortions as a source of piezoelectric/stiffness decoupling in B-doped AlScN

TL;DR

This study uses first-principles calculations to understand how boron incorporation in AlScN affects its structure and enhances piezoelectric response by symmetrizing the scandium environment.

Contribution

It reveals the structural origin of piezoelectric/stiffness decoupling in B-doped AlScN through detailed atomic and electronic analysis.

Findings

Interstitial boron atoms displace from tetrahedral sites

Boron incorporation symmetrizes scandium environment

Symmetrization correlates with increased piezoelectric response

Abstract

We present a first-principles analysis of the wurtzite pseudo-ternary (Al,Sc,B)N to elucidate the structural origin of a decoupling between stiffness $C_{33}$ and piezoelectric response $e_{33}$ upon boron incorporation, using DFT-relaxed 100-atom special quasirandom structures across a broad composition range. Pair distribution function analysis reveals interstitial threefold-coordinated boron atoms that have displaced from the tetrahedral cation site. Direct structural analysis establishes their preferential orientation along the $c$-axis and identifies a scandium-activated creation mechanism. The vertical coordination asymmetry of each cation is quantified through a site-specific axial asymmetry ratio (AAR), showing that boron incorporation progressively symmetrizes the Sc environment. Correlation with Born effective charges demonstrates that this symmetrization is the mechanism behind the piezoelectric enhancement.