PREPARATION AND CHARACTERIZATION OF TIO2-BAO-ZNO-B2O3 GLASS SYSTEMS FOR OPTICAL-DEVICES

We study the TiO2-BaO-ZnO-B2O3 glass system, where the ZnO and B2O3 co mpositions were constant and the ratio TiO2/BaO was varied from 0.87 t o 1.76. A super kanthal resistance furnace was used to melt the compou nds inside an alumina crucible, at 1200 degrees C, for 10 min. After m elting, the glasses were poured out into steel moulds and rapidly cool ed by quenching. The glasses obtained were homogeneous, bubble free an d transparent. They were characterized by X-ray diffractometry, Fourie r transform infrared spectroscopy (FTIR), UV-VIS spectroscopy, dilatom etry, density and linear refractive index. An infrared ''cut off'' cau sed by the composition influence was found in both IR and UV-vis spect ra. From dilatometry T-d and T-g were verified as being anomalous. The linear thermal expansion coefficient a presented an anomalous behavio ur in relation to TiO2 concentrations. The density and linear refracti ve index increased with increasing TiO2/BaO ratio arriving at their pe ak value of TiO2/BaO = 1.5 and then decreasing. The dependence of soft ening point T-d on the ratio TiO2/BaO exhibited the same behaviour. It is suggested that Ti4+ plays a dual part in the glass system, assumin g a predominantly tetrahedral coordination in the low titania region a nd a predominantly octahedral coordination in the high titania region. With a heat treatment of the glass around 600 degrees C, we observed a rapid change of refractive index with increasing temperature.