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 (XAFS) measurements. Diffraction results indicate that the dopant and temperature induced structural transformations involve decreases, on the average, of the tilt angle of the CuO6 octahedra to zero. The XAFS results show that locally the tilts do not disappear, the x induced phase transition has displacive and disorder components, and the T induced phase transition is purely of disorder character. It is also shown that the CuO6 octahedra tilt locally only in the [100] direction.