  The cubic spinel FeCr2S4 has been receiving immense research interest because
of its emergent phases and the interplay of spin, orbital and lattice degrees
of freedom. Despite the intense research, several fundamental questions are yet
to be answered, such as the refinement of the crystal structure in the
different magnetic and orbital ordered phases. Here, using high-resolution
synchrotron powder diffraction on stoichiometric crystals of FeCr2S4 we
resolved the long sought-after cubic to tetragonal transition at ~65 K,
reducing the lattice symmetry to I41/amd. With further lowering the
temperature, at ~9 K, the crystal structure becomes polar, hence the compound
becomes multiferroic. The elucidation of the lattice symmetry throughout
different phases of FeCr2S4 provides a basis for the understanding this
enigmatic system and also highlights the importance of structural deformation
in correlated materials.
