Unveiling Temperature‐Dependent Behavior of <scp>A</scp>l<scp>N</scp> Piezoelectric Single Crystal: Insights at the Atomic Scale

Enhancing the stability of piezoelectric properties is essential for ensuring the reliability of high‐temperature piezoelectric sensors. In this study, we have synthesized AlN piezoelectric crystals as representative materials and employed first‐principles methods to investigate their temperature‐dependent piezoelectric properties. By integrating the effects of lattice expansion and electron–phonon interactions, we accurately constructed the crystal structure of AlN across a wide temperature range and successfully predicted its piezoelectric behavior. Theoretical analysis reveals that ion polarization driven by lattice distortion and elastic softening of chemical bonds maintains the overall structural integrity of defect‐free AlN single crystals, resulting in a stable piezoelectric coefficient d 33 with a deviation of only 8.55% at temperatures up to 1300 K. However, experimental results indicate that the stability of the piezoelectric performance of the grown AlN crystals is disrupted at temperatures above 870 K. This temperature limitation is attributed to point defects within AlN crystals, particularly those caused by oxygen‐substituted nitrogen (O N ). These findings provide valuable guidance for enhancing the piezoelectric temperature stability of AlN crystals through optimized experimental conditions, such as oxygen atmosphere treatment and defect modification during crystal growth.