Altered Sr atomic environment in La_2-xSr_xCuO₄

The Sr local atomic environment in the high T_c superconductor La_2-xSr_xCuO₄ was probed by polarized XAFS measurements at the Sr K-edge on oriented powder samples with x = 0.075, 0.1 at T=20K. We confirmed that Sr indeed substitutes at the La site in this compound, but alters the first neighbor oxygen environment. This was found by determining the location of the neighboring metal atoms up to the fifth shell distances through fitting the Sr XAFS, and comparing with La K-edge polarized XAFS in the same samples and with diffraction results. The significant distortions in the immediate oxygen environment of the Sr atoms can be an important factor contributing to the mechanism of the structural and high T_c phase transitions in these cuprates.