DOPANT AND TEMPERATURE-INDUCED STRUCTURAL PHASE-TRANSITIONS IN LA2-XSRXCUO4

The local structure about La atoms in oriented La2-xSrxCuO4 samples is investigated by means of polarized x-ray absorption fine structure (X AFS) measurements. Diffraction results indicate that the dopant and te mperature induced structural transformations involve decreases, on the average, of the tilt angle of the CuO6 octahedra to zero. The XAFS re sults show that locally the tilts do not disappear, the x induced phas e transition has displacive and disorder components, and the T induced phase transition is purely of disorder character. It is also shown th at the CuO6 octahedra tilt locally only in the [100] direction.