Formation of the BiAl3(PO4)2(OH)6 Compound with a Waylandite Structure under Hydrothermal Conditions
D. P. Elovikov, М. В. Томкович, А. А. Левин, О. В. Проскурина
Abstract
The BiAl3(PO4)2(OH)6 compound with a waylandite structure has been synthesized for the first time under hydrothermal conditions at 200°С and a pressure of 7 MPa. It has been shown that the compound forms through the formation of an intermediate crystalline phase—trigonal BiPO4—and an amorphous phase of composition 0.5[3Al2O3 ⋅ 2P2O5 ⋅ 6H2O]. According to SEM data, particles resembling in morphology particles of the phase with a waylandite structure are detected after 6 h of synthesis. The formation of BiAl3(PO4)2(OH)6 in amounts distinguishable by X-ray diffraction is fixed after 12 h and almost completely ends after 48 h of hydrothermal treatment of the suspension of precursors. The formation of waylandite is confirmed by SEM and IR spectroscopy. The structure of BiAl3(PO4)2(OH)6 was refined by the Rietveld method from powder X-ray diffraction data (space group $$R\bar {3}m$$ (166) in hexagonal axes, unit cell parameters: a = 6.99608(5) Å, c = 16.1495(4) Å). Refinement gives the filling factors of unity within the standard deviation for the positions of atoms heavier than oxygen. The measured pycnometric density of the sample (4.01(8) g/cm3) is slightly lower than the density calculated from the results of structure refinement (4.235(2) g/cm3).