Understanding nanoscale phase separation in Fe(Se, Te) is essential for optimizing its microstructure to enhance superconducting properties, particularly for applications requiring high critical current density ($J_c$) and stability under external perturbations. Electron diffraction and diffuse scattering techniques have traditionally been used to probe compositional fluctuations and phase coexistence along specific crystallographic orientations. Herein, we employ transmission electron microscopy (TEM) to systematically investigate structural phase separation in ${\mathrm{FeSe}}_{0.2}{\mathrm{Te}}_{0.8}$. Our observations reveal that the dominant superconducting phase adopts a tetragonal structure, within which a nanoscale, non-superconducting hexagonal secondary phase, identified as ${\mathrm{Fe}}_7{(\mathrm{Se},\mathrm{Te})}_8$, is embedded. This hexagonal phase exhibits a well-defined orientation relationship with the tetragonal matrix, aligning specific crystallographic planes and directions, which influence phase stability and microstructural evolution. Furthermore, we examine the effects of postannealing and hydrothermal ion deintercalation (HID) treatments on phase separation. The HID treatment effectively reduces the hexagonal phase content, enhancing the homogeneity of the tetragonal matrix. These findings indicate that while phase separation-induced compositional and structural inhomogeneities serve as effective flux pinning centers to enhance $J_c$, excessive phase separation or an increased hexagonal phase fraction may degrade superconducting performance.

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• Microstructure
• Phase separation
• Iron-based superconductors
• Transmission electron microscopy