Local Sn Dipolar-Character Displacements behind the Low Thermal Conductivity in SnSe Thermoelectric
Emil S. Božin, Hongyao Xie, Milinda Abeykoon, Michelle Everett, Matthew G. Tucker, Mercouri G. Kanatzidis, Simon J. L. Billinge
Abstract
The local atomic structure of SnSe was characterized across its orthorhombic-to-orthorhombic structural phase transition using x-ray pair distribution function analysis. Substantial Sn displacements with a dipolar character persist in the high-symmetry high-temperature phase, albeit with a symmetry different from that of the ordered displacements below the transition. The analysis implies that the transition is neither order-disorder nor displacive but rather a complex crossover. Robust ferrocoupled SnSe intralayer distortions suggest a ferroelectriclike instability as the driving force. These local symmetry-lowering Sn displacements are likely integral to the ultralow lattice thermal conductivity mechanism in SnSe.