title: Structure of iron phosphate glasses modified by alkali and alkaline earth additions: neutron and x-ray diffraction studies.
abstract: The structure of iron phosphate glasses modified by additions of K(2)O and BaO, with nominal molar compositions [(1 - x)(0.6P(2)O(5)-0.4Fe(2)O(3))]xMe(y)O, where x = 0-0.4 in increments of 0.1; Me=K or Ba; and y = 1 or 2, has been investigated using neutron diffraction and x-ray diffraction techniques. Fitted coordination numbers for P-O and Fe-O showed a notable change in the P-O(NBO) and P-O(BO) contributions at greater than 20 mol% modifier addition, with barium producing a markedly larger increase in P-O(NBO) contribution than potassium. Fitting of T(N)(r) and T(X)(r) provided average n(BaO) = 9 and n(KO) = 6. Iron occurs in a range of coordination sites in these glasses: ([6])Fe(2+), ([4])Fe(3+), ([5])Fe(3+) and ([6])Fe(3+). The partitioning between these sites gives average n(FeO) = 5.2-5.8, with barium-doped glasses exhibiting higher average n(FeO) than potassium-doped glasses. The stronger depolymerizing effect of Ba(2+) than K(+) on the phosphate network, coupled with its greater ionic charge and higher Me-O, Fe-O and O···O coordination numbers, explain previously observed divergences in physical properties between the barium-doped and the potassium-doped glasses.
authors.affiliation: Materials and Engineering Research Institute, Faculty of Arts, Computing, Engineering and Sciences, Sheffield Hallam University, City Campus, Howard Street, Sheffield S1 1WB, UK. p.a.bingham@gmail.com
authors.forename: P A
authors.initials: PA
authors.lastname: Bingham
authors.forename: E R
authors.initials: ER
authors.lastname: Barney
mesh_terms: D001464:Barium / Q000737:chemistry; D001703:Biophysics / Q000379:methods; D005290:Ferric Compounds / Q000737:chemistry*; D005898:Glass / Q000737:chemistry*; D007501:Iron / Q000737:chemistry; D008422:Materials Testing; D008673:Metals, Alkaline Earth / Q000737:chemistry; D009502:Neutrons; D010100:Oxygen / Q000737:chemistry; D010710:Phosphates / Q000737:chemistry; D011188:Potassium / Q000737:chemistry; D012542:Scattering, Radiation; D014961:X-Ray Diffraction / Q000379:methods*
chemical_list: D005290:Ferric Compounds; D008673:Metals, Alkaline Earth; D010710:Phosphates; D001464:Barium; D007501:Iron; C035885:ferric phosphate; D011188:Potassium; D010100:Oxygen