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Published online by Cambridge University Press: 15 February 2011
The structure of the twin boundary in the low-temperature-orthorhombic phase of La2−xBaxCuO4 is studied using a Landau-type free energy model which reproduces the x − T phase diagram. The La2−xBaxCuO4 compound has a body-centered tetragonal (HTT) structure at high temperatures. Upon cooling it undergoes a structural phase transition to a low-temperature orthorhombic structure (LTO structure) which is caused by the tilting of the CuO6 octahedra about the (110) and (110) directions. Depending on the doping level x, the LTO structure may go through another phase transition at an even lower temperature to a low-temperature tetragonal phase (LTT phase). We find that the existence of LTT phase greatly changes the characteristics of the twin boundary in the LTO phase. LTT phase exists at twin boundaries of the LTO phase at temperatures well above the LTT to LTO transition temperature.