On the morphology and crystallography of Hg5In2Te8 precipitation in Hg3In2Te6

•The crystallography between Hg5In2Te8 and Hg3In2Te6 has been studied by TEM.•The precipitates have three variants with a 〈0 0 1〉m growth direction.•Near-CSL calculation suggests 0° or 90° mutual rotation to reach the lowest Σ value.

Transmission electron microscopy to investigate the crystallography of Hg5In2Te8 precipitation in single crystals of Hg3In2Te6. Both the matrix and precipitate phases were confirmed to have the F4¯3m space group. The lattice constant of the precipitates was measured to be a = 1.27 nm, which is approximately double that of the matrix (0.63 nm). Three crystallographically equivalent variants of the precipitate phase were observed to exhibit a cylindrical morphology, dispersed uniformly throughout the matrix. The preferred growth direction of all three variants was along 〈0 0 1〉m. The crystallographic orientation relationship (OR) between the precipitates and matrix was found to be a cubic parallel OR. High resolution imaging indicated that the precipitate–matrix interface was fully coherent. The precipitate crystals were found to correspond to the lowest sigma value of the near coincidence site lattices when performing a 0° or 90° mutual rotation. Finally, the existence of Hg5In2Te8 precipitation was found to have a negative effect on the optical properties according to the infrared transmittance measurement. The results in this paper may have a guiding significance on the relationship between the precipitate and optical properties of similar materials.