Time schedule by speaker > Koudelka Ladislav

Borophosphate glasses belong among important classes of glassy materials because they offer better thermal stability and chemical durability than phosphate glasses. Doping borophosphate glasses by heavy metal oxides like MoO3 and WO3 is interesting due to their semiconducting properties ascribed to the presence of transition metal ions in multivalent states. In this study we prepared glassy samples from the BaO-P2O5-B2O3-MoO3 systemin two compositional series (100-x)[0.5PbO-0.4P2O5-0.1B2O3]-xMoO3 and 80[0,5BaO-yB2O3-(0,5-y)P2O5]-20MoO3. Glasses were prepared from analytical grade BaCO3, MoO3, H3BO3 and H3PO4 using a total batch weight of 30g. The synthesis was carried out in platinum crucibles by heating up to 1000-1200°C. Physical properties of glasses were determined as well as their thermal behavior. For structural studies 31P and 11B MAS NMR spectroscopies were applied as well as Raman spectroscopy. 31P MAS NMR spectra showed on the depolymerization of phosphate chains with increasing MoO3 content due to the formation of Mo-O-P bonds between octahedral MoO6 structural units and tetrahedral PO4 units. 11B MAS NMR spectroscopy is able to supply information on the boron coordination in the studied glasses because these spectra possess an ability to discriminate between tetrahedral BO4 boron coordination and trigonal BO3 coordination due to the different ranges of chemical shift values for BO4 and BO3 units. The measurement of 11B MAS NMR spectra of the studied glasses with the NMR spectrometer with a high resolution (magnetic field 18.8T) revealed the formation of several different BO4 structural units containing B-O-P, B-O-B and B-O-Mo bonds. The decomposition of these spectra brought relative amounts of individual mixed structural units in these glasses.