Decoupling of lattice and orbital degrees of freedom in an iron-pnictide superconductor

The interplay between structural and electronic phases in iron-based superconductors is a central themein the search for the superconducting pairing mechanism. While electronic nematicity is competing withsuperconductivity, the effect of purely structural orthorhombic order is unexplored. Here, using x-ray diffractionand angle-resolved photoemission spectroscopy, we reveal a structural orthorhombic phase in the electron-doped iron-pnictide superconductor Pr$_4$Fe$_2$As$_2$Te$_{0.88}$O$_4$(T$_c$=25 K), which is distinct from orthorhombicity inthe nematic phase in underdoped pnictides. Despite the highelectron doping we find an exceptionally highorthorhombic onset temperature (T$_{ort}$∼250 K), no signatures of phase competition with superconductivity,and absence of electronic nematic order as the driving mechanism for orthorhombicity. Combined, our resultsestablish a high-temperature phase in the phase diagram of iron-pnictide superconductors and impose strongconstraints for the modeling of their superconducting pairing mechanism