Preparation and characterization of TiO2-BaO-ZnO-B2O3 glass systems for optical devices
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We study the TiO2-BaO-ZnO-B2O3 glass system, where the ZnO and B2O3 compositions were constant and the ratio TiO2/BaO was varied from 0.87 to 1.76. A super kanthal resistance furnace was used to melt the compounds inside an alumina crucible, at 1200 °C, for 10 min. After melting, the glasses were poured out into steel moulds and rapidly cooled by quenching. The glasses obtained were homogeneous, bubble free and transparent. They were characterized by X-ray diffractometry, Fourier transform infrared spectroscopy (FTIR), UV-VIS spectroscopy, dilatometry, density and linear refractive index. An infrared “cut off” caused by the composition influence was found in both IR and UV-vis spectra. From dilatometry Td and Tg were verified as being anomalous. The linear thermal expansion coefficient α presented an anomalous behaviour in relation to TiO2 concentrations. The density and linear refractive index increased with increasing TiO2/BaO ratio arriving at their peak value of TiO2/BaO=1.5 and then decreasing. The dependence of softening point Td on the ratio TiO2/BaO exhibited the same behaviour. It is suggested that Ti4+ plays a dual part in the glass system, assuming a predominantly tetrahedral coordination in the low titania region and a predominantly octahedral coordination in the high titania region. With a heat treatment of the glass around 600 °C, we observed a rapid change of refractive index with increasing temperature.
KeywordsTiO2 Fourier Transform Infrared Spectroscopy B2O3 Dilatometry Linear Thermal Expansion
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