Strong charge ordering above room temperature in B-site disordered electron-doped manganite SrMn_0.875Mo_0.125O_3−δ

Low- as well as high-temperature electron and x-ray diffraction studies have been carried out on a rare-earth free B-site disordered electron-doped manganite SrMn_0.875.Mo_0.125O_3−δ in the temperature range of 83–637 K. These studies reveal the occurrence of strong charge ordering (CO) at room temperature in a pseudo-tetragonally distorted perovskite phase with space group Pmmm. A non-integral modulation vector of 8.95 times along [−110] indicates a charge density wave-type modulation. The CO phase with basic perovskite structure Pmmm transforms to a charge disorder cubic phase through a first-order phase transition at 355 K. Supporting temperature-dependent measurements of resistance and magnetization show metal–insulator and antiferromagnetic transitions across 355 K with a wide hysteresis ranging from 150 K to 365 K. The occurrence of pseudo-tetragonality of the basic perovskite lattice with c/a < 1 together with charge-ordered regions with 2-dimensional modulation have been analyzed as the coexistence of two CO phases with $3d_{x^2}/3d_{y^2}$ -type and $3d_{x^2-y^2}-type$ orbital ordering. (paper)