Herringbone structure in GeTe-based thermoelectric materials

We investigated the microstructure of GeTe-based thermoelectric materials by using transmission electron microscopy. GeTe-based materials with a rhombohedral structure showed a herringbone structure, which is described as a regular arrangement of domain structures. The crystal region with different rhombohedral axis formed a domain. Domains with different variants showed alternative white and black contrast. We proposed a parallelepiped domain unit surrounded by (0 0 1), (1 1 0) and (1 1 1) planes. Domain units were arranged along a specific direction (0 0 1) and (1 1 0), which formed many colonies. Well-aligned colonies comprised various kinds of herringbone structures. Several herringbone structures were described in detail based on the transmission electron microscopy results. (C) 2015 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.