Structure and morphology of new PbBr2-B2O3 glasses analyzed by spectroscopic techniques

Abstract

Different glasses were prepared using the normal slowly cooled melting technique in the binary xPbBr2(100 − x)B2O3 (10 ≤ x ≤40 mol%) system. The methods used to analyze the microstructure of the binary PbBr2-B2O3 glasses are Nuclear Magnetic Resonance (NMR), Fourier Transform Infrared (FTIR), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and X-Ray Diffraction (XRD). The structural units of the borate matrix are established from spectroscopy of 11B NMR. The main structural species which build up the borate network are the triangle BO3, boroxol-like rings and tetrahedral BBr4 groups. FTIR spectroscopic technique also supported the existence of these borate units. The PbBr2 cannot be used as an additive modifier but it produces a crystalline Pb2B5O9Br mixture that is impeded in the glass matrix. The species BO3 is the primary complement of the species Pb2B5O9Br. NMR and FTIR spectroscopy confirmed the nature of BO3 components. On the other hand, there is no evidence of BO4 species in the material being studied. NMR spectroscopy reveals a very low concentration of (BBr4) tetrahedral (boron combined with Br). In these materials, the TEM and SEM micrographs as well as EDP (electron diffraction patterns) and x-ray diffraction analyses reported the development of crystalline Pb2B5O9Br phases. The electrical resistivity is extremely high in the investigated samples, their value close to the fused B2O3 limit.