Although crystalline solids are characterized by their periodic structures, some are only periodic on average and deviate on a local scale. Distinct local orderings can exist with identical periodic structures making their differences hidden to normal diffraction methods. Using x-ray scattering we investigate the thermoelectric half-Heusler, Nb1-xCoSb, with high vacancy concentrations, where signs of local order have been attributed to differences in stoichiometry. We show that the composition is actually always very close to x = 1/6 irrespective of nominal sample composition, and that the synthesis method controls the local order. The vacancy distribution is shown to follow a vacancy repulsion model, and local structural relaxations around the vacancies are characterized. Control over the local structure provides a new frontier for tuning material properties.
@article{arxiv.2103.08543,
title = {Tuneable local order in thermoelectric crystals},
author = {Nikolaj Roth and Jonas Beyer and Karl F. F. Fischer and Kaiyang Xia and Tiejun Zhu and Bo Brummerstedt Iversen},
journal= {arXiv preprint arXiv:2103.08543},
year = {2021}
}