Zr4O5N2-intergrowth of fluorite and bixbyite anion layers formed by coupled site-selective anion and vacancy ordering

The defect fluorite Zr4O5N2 is presented. A simple layered intergrowth of the important bixbyite and fluorite structure types, it displays an A(4)X(7) vacancy ordering alternative to that in the pyrochlore and other structures. This ordering is stabilized by proximity of the highly charged N3- anions to the bixbyite-type face diagonal vacancy neighbors in the initially cubic cation coordination environment of fluorite. The existence of this simple structure demonstrates the potential of substitution on the anion sublattice to control the structures of ionic defect systems.