Refinement of atomic position in purely ionic materials using perturbed angular correlation spectroscopy

In a number of isostructural sesquioxides M2O3 (M=Sc, In, Y, Yb, Dy, Ho, Sm, Gd) with the bixbyite structure the electric field gradients at substitutional 111 Cd nuclei show a regular and smooth dependence on the lattice constant. The electric field gradients allow the positions of all atoms in the unit cell to be determined with an accuracy of 0.3 pm by means of a simple point-charge model; this is typically five times better than the data available from neutron and x-ray diffraction experiments