To resolve the controversy in the literature, we studied the extensively twinned domain structure of ferroelectric germanium telluride (GeTe) to formulate a comprehensive three-dimensional domain description. The observed herringbone-domain structure arises due to the displacive phase transformation from a cubic to rhombohedral symmetry upon cooling. Using a simple model based on minimizing global shape change and local (interface) strain, a mixed system of {010} and {011} twin boundaries is argued to be the most energetically favorable structure and the only solution to obtain a fully compatible domain structure. Using scanning and transmission electron microscopy, we identified the twin boundary orientations together with the arrangement of local distortion directions in the submicron size domains and confirm that the proposed domain structure is indeed the prevalent one. Because our model and analysis do not assume material-specific parameters other than the phase transition, this analysis is argued to be valid for a wide range of materials showing domain formation after a cubic to rhombohedral phase transformation. Indeed, we demonstrate that our model also holds in the case of LaAlO3.
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