STRUCTURAL-ANALYSES ON LA2-XSRXCUO4-DELTA CRYSTALS

We present results of single crystal neutron diffraction experiments on La2-xSrxCuO4-delta. The analysis of the temperature dependence of the La-O bond lengths shows that almost the entire thermal contraction of La2CuO4 between 540 K an 50 K is due to the decrease of the LaO9 polyhedron, the Cu-O bond distances remain almost constant. Doping of La2CuO4 with Sr (or additional O) decreases both Cu-O bond lengths. The large thermal parameters especially of the apical O indicate the instability of all examined crystals against a second phase transition.