Non-random cation distribution in hexagonal Al0.5Ga0.5PO4

Based on powder X-ray diffraction and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) investigations of mixed phosphate Al0.5Ga0.5PO4, prepared by co-precipitation method followed by annealing at 900 °C for 24 h, it is shown that Al0.5Ga0.5PO4 phase crystallizes in hexagonal form with lattice parameter a=0.491(2) and c=1.106(4) nm. This hexagonal phase of Al0.5Ga0.5PO4 is similar to that of pure GaPO4. The 31P MAS NMR spectrum of the mixed phosphate sample consists of five peaks with systematic variation of their chemical shift values and is arising due to existence of P structural units having varying number of the Al3+/Ga3+ cations as the next nearest neighbors in the solid solution. Based on the intensity analysis of the component NMR spectra of Al0.5Ga0.5PO4, it is inferred that the distribution of Al3+ and Ga3+ cations is non-random for the hexagonal Al0.5Ga0.5PO4 sample although XRD patterns showed a well-defined solid solution formation.