Influence of deficient sites on the structural stability of θ‐ <scp> Al ₂ O ₃ </scp>

Abstract As an important transitional alumina phase, θ‐Al 2 O 3 , its structural stability directly impacts the thermodynamic properties and potential applications. In this study, the unit cell structure of θ‐Al 2 O 3 was determined through Rietveld XRD refinement, and it was found that the occupancies of both two types of Al sites and two of three types of O sites were less than 1. A 1 × 5 × 2 supercell (Al 80 O 120 ) was constructed, and the effect of each type of defect on the stability of the structure was determined by molecular dynamics simulations and the calculations of the probability distribution function of the distance to mass center (P(r)) during heating. It was found that defects at the Al1 sites are more likely to cause structural instability than those at the Al2 sites; the O3 defect brings poor thermal stability to the structure due to its low occupancy.