Stacking faults and other topological defects in ferroics can have a significant influence on the electronic and mechanical properties of the material. Here, regular stacking faults in the tetragonal tungsten bronze material Sr2NaNb5O15 are investigated through transmission electron microscopy, symmetry mode analysis and machine-learned force-field calculations. It is shown that the faults, with a fault vector of 41[2ˉ12]o, annihilate in sets of four in the material, owing to the 41 unit cell displacement along the b-axis. The four resulting domains emerge as four possible directions of the S3 order parameter, related to NbO6 octahedral tilts in the material. Force-field calculations reveal that the stacking faults are likely placed at positions where the octahedra in neighbouring domains have similar magnitudes of rotation, and that the estimated stacking fault energy is 46 mJ/m2. The investigation shows that the stacking faults have a significant local effect on the polar modes present in the structure, and therefore could affect the ferroelectric properties.
@article{arxiv.2511.06983,
title = {The Microscopic Structure of Stacking Faults in Sr$_2$NaNb$_5$O$_{15}$},
author = {Robin Sjökvist and Yining Xie and Zabeada Aslam and Andy P. Brown and Nicholas C. Bristowe and Mark S. Senn and Richard Beanland},
journal= {arXiv preprint arXiv:2511.06983},
year = {2025}
}