Non-random cation distribution in hexagonal Al 0.5Ga 0.5PO 4

Abstract

Based on powder X-ray diffraction and 31P Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) investigations of mixed phosphate Al 0.5Ga 0.5PO 4, prepared by co-precipitation method followed by annealing at 900 °C for 24 h, it is shown that Al 0.5Ga 0.5PO 4 phase crystallizes in hexagonal form with lattice parameter a=0.491(2) and c=1.106(4) nm. This hexagonal phase of Al 0.5Ga 0.5PO 4 is similar to that of pure GaPO 4. 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 Al 3+/Ga 3+ cations as the next nearest neighbors in the solid solution. Based on the intensity analysis of the component NMR spectra of Al 0.5Ga 0.5PO 4, it is inferred that the distribution of Al 3+ and Ga 3+ cations is non-random for the hexagonal Al 0.5Ga 0.5PO 4 sample although XRD patterns showed a well-defined solid solution formation.