The structures and properties of Ba sub 2 YCu sub 3 O sub 6.

The structure of Ba sub 2 YCu sub 3 O sub 6 has been determined by neutron diffraction powder profile analysis. The compound is obtained from the superconducting Ba sub 2 YCu sub 3 O sub 7 by heating in atmospheres of reduced oxygen partial pressures. A pressed pellet of Ba sub 2 YCu sub 3 O sub 6 exhibited semiconductivity with a band gap of 0.21eV from 125-300K. The crystallographic unit cell is tetragonal P4/mmm with a=3.8570(1)angstroms and c=11.8194(3)angstroms. The cations are in a perovskite type arrangement, with Ba and Y ordered on the A site to give a cell tripled along c. The oxygens occupy only 2/3 of the perovskite anion sites and are ordered such that 1/3 of the Cu is two- fold coordinated and 2/3 is five-fold coordinated.