G. Wignall, R. Rothon, G. W. Longman
May 1, 1977
Citations
1
Influential Citations
23
Citations
Journal
Journal of Materials Science
Abstract
An investigation of the molecular structure of amorphous aluminium phosphate, prepared from a recently discovered complex (AlPO4 · HCl · 4C2H5OH), has been carried out using radial distribution function (RDF) techniques. Studies were made on two samples, one prepared by decomposing the solid complex and the other from powder produced by evaporating to dryness a solution of the complex in methanol and then decomposing and grinding the solid obtained. RDF curves were obtained from both samples, and were found to closely resemble that previously reported for vitreous silica. The short range order in both samples is similar to that in vitreous silica, with aluminium and phosphorous atoms occupying positions in aluminium phosphate similar to the positions of silicon atoms in silica. This structure is consistent with the crystal chemistry of aluminium phosphate.It is possible to assign all the peaks in the RDF plots out to values of r∼5 Å to known inter-atomic distances. The peak at 1.6 Å represents the Al-O and Al-P bond lengths, and is broader than the corresponding Si-O peak in vitreous silica, as the Al-O and P-O bonds are respectively slightly longer (Al-O) and shorter (P-O) than the equivalent Si-O bonds. Subsequent peaks result from the O-O distances (∼ 2.6 Å); the Al-Al, Al-P and P-P distances (∼ 3.1Å); the Al-second O and P-second O distances (∼ 4.2 Å), and O-second O, Al-second Al, P-second P and Al-second P distances (∼ 5.0 Å). The sample prepared from the methanolic solution shows some small additional peaks in the region 4 to 5 Å, indicating more order in the second neighbour distances.Analysis of the P-O and Al-O peak area indicates that both P and Al atoms are co-ordinated to four network oxygen atoms at a distance ∼ 1.6Å, and that absorbed water also co-ordinates to one or both atoms with a P-O and/or Al-O distance of ∼ 1.6 Å.