The local atomic structure of SnSe was characterized across its orthorhmbic-to-orthorhombic structural phase transition using x-ray pair distribution function analysis. Substantial Sn off-centering distortions persist in the high symmetry high temperature phase, with symmetry different from that of ordered distortions below the transition. The analysis implies that the transition is neither order-disorder nor displacive, but rather a complex crossover where the character of coupling changes from 3D-like at low temperature to 2D-like at high temperature. Robust ferro-coupled SnSe intra-layer distortions suggest a ferroelectric-like instability as the driving force. Complex local Sn off-centering is integral to the ultra-low lattice thermal conductivity mechanism in SnSe.
@article{arxiv.2301.05773,
title = {Nanoscale Sn off-centering behind low thermal conductivity in SnSe thermoelectric},
author = {E. S. Bozin and H. Xie and A. M. M. Abeykoon and S. M. Everett and M. G. Tucker and M. G. Kanatzidis and S. J. L. Billinge},
journal= {arXiv preprint arXiv:2301.05773},
year = {2023}
}