An x-ray scattering study of the structural phase transition in La2-xSrxCu0.99Fe0.01O4 (x=0.20)

We report a comprehensive x-ray scattering study of the low-temperature orthorhombic (LTO)-high-temperature tetragonal (HTT) structural phase transition in 1% iron-doped La2-xSrxCuO4 (x = 0.2). The superlattice (032) peak intensity and the width are investigated in detail for a wide temperature range. We found that the structural phase transition is not sharp and the tilt ordering of the CuO6 octahedra persists above the transition temperature T-S (approximate to 77 K). Even at room temperature, the superlattice peak is still observable. The structural phase transition is identified as an order-disorder type phase transition. We found that the tilt ordering in our iron-doped material is always short-ranged, and in the HTT phase the correlation between the tilts along the b axis is better preserved than that along the a axis. Moreover, we identify the role of the Fe as the nucleation centers of the LTO domains in the structural phase transition.