Bismuth-borate glasses and vitroceramics belonging to x Bi 2 O 3 · (100 - x) B 2 O 3 system, 0 ≤ x ≤ 93, doped with 0.5 mol% MnO are investigated by 11 B Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR). The 11 B MAS NMR results indicate the presence of three- and tetra-coordinated boron in all investigated bismuth borates. While the fraction of the tetra-coordinated boron present a large maximum in the range 20 ≤ x ≤ 60 in the bismuth-borate glasses, this maximum is reduced to the range 20 ≤ x ≤ 37.5 in the samples obtained after heat treatment. Crystalline phases are developed in the samples with high bismuth content, x ≥ 60, by heat treatment at 550°C, in which two types of three-coordinated boron are identified. The mean values of the NMR parameters like chemical shift, asymmetry parameter and quadrupolar coupling constant are less influenced by the bismuth/boron ratio, showing that boron structural units are relatively stable on the entire investigated composition range.
Bismuth Borates: Two New Polymorphs of BiB3O6.
