Structure-property relationships in the layered cuprate la_2-xsr_xcusno₆

In an attempt to induce a metallic or superconductive state in the layered cuprate La₂CuSnO₆, the series La_2-xSr_xCuSnO_6-x/2+δ (x = 0.00, 0.05, 0.10, 0.125, 0.15, 0.175, 0.20) was prepared. A solid solution forms for 0.00 < x < 0.175, the overall oxygen content is 6.00 (3), and the samples are antiferromagnetic semiconductors. From neutron diffraction experiments, the compounds possess distinct copper-oxygen and tin-oxygen layers. There is a mismatch at the interface of the layers, which results in expansion of the copper-oxygen bond lengths (1.99 Å average). The copper is oxidized upon addition of strontium; however, in contrast to p -type cuprate superconductors, the in-plane copper-oxygen bond lengths increase and the axial bonds decrease. The interleaved tin-oxygen layers have a dramatic effect on the crystal chemistry, electronic structure, and properties. The electronic consequence is that empty upper and filled lower dx² - y² bands (upper and lower Hubbard bands) remain separated and narrow upon oxidation, which presumably prohibits superconductivity.