The crystal structure of the high temperature superconductor La sub (1.85) Sr sub (.15) CuO sub 4 above and below T sub c.

The crystal structure of La sub (1.85) Sr sub (.15) CuO sub 4 has been determined at 300, 60, and 10k by neutron diffraction powder profile analysis. The structure is of the tetragonal K sub 2 NiF sub 4 type at ambient temperature, but undergoes an orthorhombic distortion near 200K which buckles the copper- oxygen planes. The crystal structure of the orthorhombic phase is not significantly different above and below T sub c. The copper-oxygen coordination polyhedron changes shape in a subtle manner at the tetragonal to orthorhombic phase transition, but is unchanged at T sub c.