The structure of solid solutions of ZrO2containing 18%, 22% and 26% YO1.5as well as 26% YbO1.5have been examined by Bragg neutron diffraction and the diffuse scattering of long wavelength (7 AA) neutrons. The evidence points to a relaxation (0.36 AA) of the six nearest-neighbour oxygen ions surrounding an anion vacancy and there are probably similar but smaller relaxations of the four neighbouring cations which include two Y3+(or Yb3+) ions to maintain local charge neutrality. At the highest trivalent ion concentration studied there are signs of preferential association of oxygen vacancies and at the lowest vacancy concentration the presence of some tetragonal phase is indicated, possibly as an intergrowth.
