Mechanochemical–thermal preparation and structural studies of mullite-type Bi2(GaxAl1−x)4O9 solid solutions

A series of Bi2(GaxAl1−x)4O9 solid solutions (0≤x≤1), prepared by mechanochemical processing of Bi2O3/Ga2O3/Al2O3 mixtures and subsequent annealing, was investigated by XRD, EDX, and 27Al MAS NMR. The structure of the Bi2(GaxAl1−x)4O9 solid solutions is found to be orthorhombic, space group Pbam (No. 55). The lattice parameters of the Bi2(GaxAl1−x)4O9 series increase linearly with increasing gallium content. Rietveld refinement of the XRD data as well as the analysis of the 27Al MAS NMR spectra show a preference of gallium cations for the tetrahedral sites in Bi2(GaxAl1−x)4O9. As a consequence, this leads to a far from random distribution of Al and Ga cations across the whole series of solid solutions.