Characterisation of glasses in the TeO_2-WO_3-PbO system

摘要

As potential candidates for photonic devices, non-linear materials and coatings, 22 glasses in the TeO_2-WO_3-PbO system have been formulated and prepared by conventional melting at temperatures ranging between 710 and 750 deg C. The glass forming area has been determined for a wide region of the corresponding ternary diagram. Structural characterisation of the glasses was conducted through FTIR spectrometry and the variation of density values, which allowed calculation of the glass molar volume and the oxygen molar volume. UV-VIS spectra were recorded to determine optical absorption/transmission and energy gap values. Likewise, such results were correlated with the glasses composition and their ability for optical materials. DTA curves yielded data of transition temperature (T_g), onset crystallisation temperature (T_c) and the thermal stability range of glasses. Crystalline phases formed in devitrified and partially devitrified glasses were detected by X-ray diffraction. The properties and structural features of glasses were discussed in terms of their relative proportion of former/modifier oxides. The main glass former oxide is TeO_2, which arranges [TeO_4] groups with tetrahedral coordination, while PbO plays as glass modifier oxide. Tungsten oxide is incorporated as network former, alternating with TeO_2 and forming mixed linkages Te-O-W and W-O-W. WO_3 is the component that contributes most to increase the glass transition temperature, and to decrease both the oxygen molar volume and the thermal expansion coefficient.