Abstract
In the concentration range of the local Tc minimum in La2-xBaxCuO4 (0.10≤×≤0.15), below 60K, there is a low temperature tetragonal (LTT) structure (space group P42/ncm). With an increase in temperature, the structure becomes orthorhombic (LTO, space group Bmab), then above 140K becomes tetragonal (HTT) with the space group I4/mmm.The transition from HTT to LTO during cooling generates twins, and the twin morphology persists even below 60K. This is inconsistent with a pure LTT phase, since twinning is associated with an orthorhombic symmetry. To address the issue of the LTO/LTT phase transition, we performed in-situ experiments with a 200 keV TEM equipped with a liquid H2 specimen holder.Fig.1(a) and (b) show selected area diffraction patterns taken at 15K in the (001)* and (101)* zone, respectively. During in- situ cooling and the LTO/LTT transition, the (101)* diffraction pattern remains the same because h+l=2n reflections are allowed in both LTO and LTT.
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