Defect Structure of (B2O3)100-x (Bi2O3)x glasses

Bismuth borate glasses with composition (100-x)B 2 O 3x (Bi 2 O 3 ) (where x is in mol.% ranging from 25 -50 in steps of 5) have been prepared by using melt quenching technique.Positron annihilation lifetime (PAL), Fourier transform infra-red (FT-IR) and X-ray diffraction (XRD) measurements have been performed to study the amorphous and defect structure as well as the vibrating band structure.PAL results have revealed weak formation of ortho-positronium (o-Ps) at amorphous sites.At low concentration, the pore size at these sites increases from 2.5 nm to 3.5 nm with increase of Bi 2 O 3 content, then show weak decrease to 3nm at higher concentration showing also a reduction in the relative pore fraction from 9.8% to 1% in agreement with XRD spectra, which indicate the presence of some peaks associated with Bi 2 O 3 phase.On the other hand, the variation of the annihilation parameters at defects, suggest strong trapping of the free positron at non-bridging oxygen (NBO) bonds, which have been determined by FT-IR.In addition, IR spectra revealed the presence of some bonds that are assigned to vibrations of Bi-O bonds from [BiO 3 ] pyramidal and [BiO 6 ] octahedral units and B-O bonds from [BO 3 ] and [BO 4 ] units.