Structural disorder in Ba0.6Sr0.4Al2O4

The structural disorder in Ba0.6Sr0.4Al2O4 (space group P6322) was investigated by X-ray powder diffraction and selected-area electron diffraction (SAED). The initial structural model was determined using direct methods, and it was further modified by the combined use of Rietveld method and maximum-entropy method (MEM). MEM-based pattern fitting method was subsequently applied, resulting in the final reliability indices of Rwp=9.61%Rwp=9.61%, Rp=6.96%Rp=6.96%, RB=1.40%RB=1.40% and S=1.25S=1.25. The electron density distribution was satisfactorily expressed by the split-atom model in which the strontium/barium and oxygen atoms were split to occupy the lower symmetry sites. The diffuse scattering in SAED was mainly attributable to the positional disorder of oxygen atoms.

Two-dimensional electron density distribution map showing positional disorder of oxygen atoms in Ba0.6Sr0.4Al2O4.Figure optionsDownload as PowerPoint slide