Computational simulations of δ-Bi2O3. I. Disorder
Abstract Four potential models, varying from a rigid-ion model to a fully-polarized ion model, have been employed in this computational simulation of the fluorite phase of bismuth oxide. Electrostatic considerations suggest a basic ordering of the 25% vacant anion sites. It is shown that isolated defects in this lattice have a negative formation energy, but that these defects do not continue to form without limit because the lattice with ordering is more stable than one with ordering. Also, defects tend to form chains and symmetric clusters but their concentration becomes limited by non-additive interactions between nearby defects. Calculations show that cube-edge interstitials, relaxed slightly towards the centre of adjacent empty cubes, are metastable. Also, Bi 3+ cations undergo displacements away from vacancy pairs. Such cube-edge interstitials and cation displacements are features of the neutron scattering results for the yttria-stabilized fluorite phase of Bi 2 O 3 .