27Al MAS NMR study on anion coordination around Al 3+ in AlF 3-BaF 2-BaCl 2-CaF 2-YF 3-EuF 3 glasses

Abstract

27Al MAS NMR spectra of 12 fluoroaluminate crystals with known crystal structures and 40AlF 3·(20- x)BaF 2· xBaCl 2·20CaF 2·17YF 3·3EuF 3·glasses ( x=0,3,6,9 and 12) in mol% were measured to examine the anion coordination environments around Al 3+ in the glasses. All the glasses gave NMR spectra with very similar line profiles, indicating that the anion coordination environments around Al 3+ are almost the same, and that only F − bonds to Al 3+ regardless of the substitution of Cl for F. A comparison of the isotropic chemical shift values and the line profiles between glasses and fluoroaluminate crystals concludes that only AlF 6 octahedra are present in the glasses and that these AlF 6 octahedra mainly build up chains and/or rings by sharing the two corners in cis-configuration. Moreover, fairly sharp and symmetric line-profiles in the glasses suggest considerably high symmetry in the F −-coordination around Al 3+.