Sequential Jahn–Teller and tilting transitions in the mixed Ru Mn perovskite SrRu0.5Mn0.5O3

The temperature dependence of the structure of the mixed metal perovskite SrRu0.5Mn0.5O3 has been studied from room temperature to 800 ∘C. Below 400 ∘C, the structure is tetragonal in space group I4/mcmI4/mcm. This structure is characterised by cooperative tilting of the (RuMn)O6 octahedra that also exhibit a large JT type elongation. Heating reduces the magnitude of the tetragonal distortion and SrRu0.5Mn0.5O3 undergoes two apparently continuous transitions. The first near 250∘ does not involve a change in symmetry but rather is due to orbital melting and the removal of the cooperative JT distortion of the (RuMn)O6 octahedra, and the second is associated with the removal of the cooperative tilting of the octahedra, and results in an increase in symmetry to cubic in Pm3¯m.