Vertical boundary at x≈0.11 in the structural phase diagram of the La1-xSrxMnO3 system (0.08≤x≤0.125) -: art. no. 024431

The structural phase diagram of the La1-xSrxMnO3 system in the compositional range 0.08 less than or equal tox less than or equal to0.175 has been investigated by high-resolution synchrotron x-ray powder diffraction techniques between 20-600 K. Recent studies have reported that there is an unusual reentrant-type phase transition in this range involving an abrupt change in lattice parameters but no change in the crystal symmetry, which remains orthorhombic Pbnm. The transition to the reentrant phase is from a ferromagnetic metallic to a ferromagnetic insulating phase with some unusual properties. Our results demonstrate that for samples with x = 0.11-0.175 there exist two lower-symmetry structural regions having monoclinic and triclinic symmetry, respectively. There is a sharp first-order transition from the monoclinic to the triclinic phase coinciding with the transition to the ferromagnetic insulating phase, and an abrupt crossover from the orthorhombic Pbnm region with a near-vertical phase boundary just below x=0.11. The new phases indicate the presence of some novel type of orbital ordering unlike that found in LaMnO3.