THERMAL-EXPANSION MEASUREMENTS IN A LA1.85SR0.15CUO4 SINGLE-CRYSTAL SUPERCONDUCTOR BY X-RAY-DIFFRACTION

Lattice parameter measurements have been made in a La1.85Sr0.15CuO4 single crystals superconductor between 4.2 K and room temperature by the X-ray Bond method. A structural distortion near the superconducting transition temperature of 33 K has been observed. The lattice spacing in the c-direction increases below the superconducting transition temperature with decreasing temperature. The change in the lattice parameter, DELTA-c/c0, between 4.2 K and 33 K, is 2x10(-5). Along a direction perpendicular to the c-axis, on other hand, the lattice spacing decreases more rapidly than expected from normal thermal contraction. The possible importance of these results for existing theories of high temperature superconductivity is noted.