The structure of vitreous boron oxide

Abstract

A new study of the structure of vitreous boron oxide has been made under greatly improved conditions. Using Rh K~ radiation with the method of fluorescence excitation, reliable intensity values were measured to 4n sin 0/2 = 20 ,~-1, and a rigorous interpretation was obtained in terms of pair functions. Each boron is triangularly surrounded by 3 oxygen atoms with a B-O distance of 1"37 A. Each oxygen atom is bonded to 2 boron atoms. The major part of the glass is made up of boroxol groups B306 (a hexagonal ring of 3 boron atoms and 3 oxygen atoms with 3 corner oxygen atoms outside the ring). These groups are linked together by sharing the corner oxygen atoms, with randomness in orientation about the B-O bond directions at the shared oxygen atoms. Within the ring the B-O-B angle is 120 ° and at the shared oxygen it is approximately 130 °. There is satisfactory agreement between the calculated and measured pair function distribution curves. In vitreous B203 the scheme of bonding does not fill space, and any boroxol group has neighboring groups which are not directly connected to it by B-O and O-B bonds. The measured pair function areas indicate neutral atoms, so that the bonding is predominantly covalent.

Molecular Dynamics Investigation on Microstructure and Void in Amorphous SiO<SUB>2</SUB>

“…2(c) and 3(c)). These results were close to those of the experiment data of 3) and showed some distortions compared to an ideal tetrahedron with O-Si-O bond-angle of 109. 4 .…”

“…Its structural characteristics, such as bondangle, coordination number, and ring structure, have been considerably investigated [1][2][3][4][5] because of their important role on the structural and functional behavior. In contrast, voids and their distributions inside SiO 2 have studied little, although the importance of them is well known through their absorbent and diffusive capacities.…”

Hyper-Raman scattering analysis of the vibrations in vitreous boron oxide

“…The proposal that it might relate to a coherent symmetric stretch of the bridging oxygens over the entire network 33 should be abandoned in this particular case, since the large spread in -B-O-B-angles outside boroxol rings could not produce such a narrow width. Raman scattering from isotopically pure samples containing 10 32 . It is the remarkable regularity of the boroxols that accounts for the narrowness of this vibration.…”

“…For this reason, observing vibrations in the crystal would be of very limited guidance to assign the vibrations in the glass. The existence of boroxol rings in the glass is known from x-ray diffraction 10 , NMR 11 , RS 12 , and neutron scattering 13 . Although boroxols result from the bonding of three BO 3 triangles, these ESUs are special in that their internal B-O-B angle is ∼ = 120…”

Oxidation stability of boride coatings

“…B 2 O 3 has not been detected by XRD in the present case. This could be related to the noncrystalline ("glassy") nature of this phase [40].…”