Yttrium rhenium oxide, Y_7ReO_(14-δ): a cubic fluorite superstructure

摘要

The crystal structure of yttrium rhenium oxide, Y_7ReO_(14-δ), is a 2 * 2 * 2 superstructure of the CaF_2 structure, space group Fm(3-bar)m, a=10.4770(14) A. The 32 cations within the unit cell are distributed with yttrium on the (4a)- and (24d)-sites and with rhenium on the (4b)-site. The 64 oxygen atoms occupy two (32f) sites (x,x,x), O(1) with x_1=0.1351(9) and O(2) with x_2=0.6054(11), in the undistorted fluorite structure x=0.125 and 0.625. The site occupation factor for the O(2) site is only 77(8)% in agreement with the maximum of 75% for δ=0 in the proposed stoichiometry. The electrical DC conductivity, measured on a single crystal, reveals semiconducting behavior between 165 and 265 K with a band gap of 157.4 meV.