Structural phase transition below 250 K in superconducting K${}_{0.75}$Fe${}_{1.75}$Se${}_2$

A. Ignatov, A. Kumar, P. Lubik +5

Vibrational properties of iron-chalcogenide superconductor K${}_{0.75}$Fe${}_{1.75}$Se${}_2$ with $T_c\sim$ 30 K have been measured by Raman and optical spectroscopies over temperatu…