We resolve the long-standing discrepancy between theoretical material constants and experimental observations of the dielectric response in scandium aluminum nitride (ScAlN). While first-principles calculations of the rigid lattice predict a permittivity of about 11.7, experiments consistently report values near 15. We demonstrate that this "high K" behavior is a manifestation of electromechanical inflation, where the enormous internal electric fields of polar heterostructures induce macroscopic lattice strain via the inverse piezoelectric effect. By applying stress-free mechanical boundary conditions to the coupled equations of state, we derive an analytical relation for the effective permittivity: epsilon_eff=epsilon_33^S + e_33^2/C_33. This model quantitatively accounts for experimental observations across the ScAlN alloy range and defines the fundamental limit of the rigid-lattice approximation in highly polar semiconductors.
@article{arxiv.2605.03765,
title = {The high K anomaly in ScAlN explained},
author = {Ilan Shalish},
journal= {arXiv preprint arXiv:2605.03765},
year = {2026}
}