Structural effects of Mn-substitution in β-FeSe

In the present work the structural and microstructural properties of Mn substituted β-FeSe are inspected by using high-resolution synchrotron X-ray powder diffraction data collected between 10 K and 150 K. It is demonstrated that the thermal increase of the structural strain in the tetragonal phase progressively breaks the 4-fold symmetry at the local scale, qualitatively tracing the development of anisotropy measured in some physical properties, generally ascribed to nematicity. This result points to a close relationship and interplay between structural strain and physical properties; with this notion, the structural strain can be considered as the origin of the unexpected anisotropy observed in some physical properties. Remarkably, incommensurate satellite peaks are observed in the diffraction pattern collected in the low-temperature orthorhombic phase field, likely related to the occurrence of a charge-density-wave instability.