Structural analysis of 12CaO.7Al2O3glass

Structural studies of lead aluminate glasses

“…The lead ion may be surrounded either by a symmetric distribution of ligands, or an asymmetric distribution of ligands with an identifiable void in the distribution of bonds to the ligands. For low coordination numbers (2)(3)(4)(5) the environment is asymmetric with short bond lengths, whilst for high coordination numbers (9 and 10) the environment is symmetric with long bond lengths. For intermediate coordination numbers (6)(7)(8) both types of environment are found.…”

“…There have been no previous structural studies of lead aluminate glasses, but studies of calcium aluminate glasses using XRD [5], nuclear magnetic resonance (NMR) [6], neutron diffraction [7] and molecular dynamics modelling [8] indicate that the aluminium, at these concentrations, should be four coordinated, while neutron diffraction work [9,10] and extended X-ray absorption fine structure (EXAFS) studies [11] on lead gallates, as well as NMR [12], XRD [13] and Raman spectroscopy [14] studies on lead silicates, suggest that the lead will be in either PbO 3 trigonal pyramids or PbO 4 square pyramids.…”

Molecular dynamics simulations of calcium aluminate glasses

“…This is not surprising since the reliability of the MD simulations is limited to a distance of about half the smallest box length; a larger box size would be required in order to investigate the longer range correlations in detail, but was not used here because our interest was in the short-range order. Table 5 shows the comparison of interatomic distances and coordination numbers for the simulations with the results of X-ray diffraction [4], neutron diffraction [5,6], combined neutron and X-ray diffraction [7] and NMR [8]. The interatomic distances for the simulations were determined from the positions of the first maximum in the appropriate PCF.…”

“…In the first reported diffraction study of calcium aluminate glasses, Morikawa et al [4] used X-ray diffraction on a sample with 36.8 mol% Al 2 O 3 to show that Al is coordinated by 4.2 oxygens at a distance of 1.77 Å , whilst Ca is coordinated by 5.6 oxygens at a distance of 2.37 Å . More recently Hannon and Parker [5] used neutron diffraction on splat-cooled samples with 30 and 38 mol% Al 2 O 3 to show that aluminum is tetrahedrally coordinated by oxygen and calcium is coordinated by four oxygen atoms at about 2.34 Å .…”

Raman and 27Al NMR structure investigations of aluminate glasses: (1−x)Al2O3−x MO, with M=Ca, Sr, Ba and 0.5<x<0.75)

“…The structure of calcium aluminate has already been described in number of recent studies [7][8][9][10][11][12][13][14][15][16][17][18]. To understand the influence of alkaline-earth on the aluminate glass structure we substituted Ca by alkaline-earth elements, Sr or Ba where radius of element increases with the weight [19].…”