Crystal structure, phase transitions, and magnetic properties of titanium doped La0.5Sr0.5MnO3 perovskites

International audience ; The current paper investigates the effect of titanium substitution on the structure as well as the magnetic properties of La0.5Sr0.5Mn1−xTixO3 (0≤x≤0.5) polycrystalline powder. The samples studied crystallize in a distorted perovskite structures of tetragonal (space group I4/mcm) symmetry with octahedral tilting scheme ( a 0 a 0 c − ), leading to the absence of octahedral tilting all along two perovskite main directions and to an out-of-phase along the third direction, or rhombohedral (space group R 3 ¯ c) symmetry with octahedral tilting scheme ( a − a − a − ) yielding to out-of-phase along the three perovskite main directions. As the Ti content increases, a better matching of the (Mn/Ti)–O distances and (Mn/Ti)–O–(Mn/Ti) bond angle occurs. This phenomenon is created by an elongation of the (Mn/Ti)–O distance, as Mn4+ is substituted by the larger ion Ti4+. In the whole compositional range, the symmetry-adapted to atomic displacements, responsible for the out-of-phase tilting of the (Mn/Ti)O6 octahedra, stays active, anticipating tetragonal-to-rhombohedral phase transition. Taking in to account what has been explained above, measurements of magnetic properties show a decrease of magnetic ordering temperature when Ti content increases, which in turn leads to the diminution of the exchange interaction caused by reducing the FM coupling and the replacement of neighboring manganese Mn3+–O–Mn4+ by Mn3+–O–Ti4+ bonds. This phenomenon results in broadening of the paramagnetic to ferromagnetic phase transition range. Further changes in magnetic properties with the increase in Ti concentration are studied.