Investigations of thermal, structural and optical properties of tellurite glass with WO3 adding

Abstract

Tellurite glasses with the molar composition (89-x) TeO2–10TiO2–1Nd2O3–xWO3 (x=0, 10 and 20mol%) were prepared by the conventional melt-quenching technique. The effects of WO3 concentration on the structural, thermal and optical properties of tellurite glasses have been discussed. From the differential scanning calorimetry measurements, thermal properties such as glass transition temperature Tg, crystallization temperature Tx, and thermal stability ΔT are estimated. It was found that ΔT increases with the increase of WO3 composition which can indicate a reinforcement of the glassy network. Both Raman and FTIR results show that the addition of WO3 induced a depolymerisation of tellurite glass since the Te–O–Te inter-chain linkages are progressively substituted by stronger Te–O–W bridges that are at the origin of the increase of the thermal stability of the glass.The optical band gap energy values corresponding to the direct and indirect allowed transitions and the Urbach energy values of the prepared tellurite glasses have been calculated from optical absorption edges. The results show an important decrease of the optical band gap with the increase of WO3 concentration. It was assigned to W6+ ions that could have a role as network modifier. The Urbach energy was found to decrease with WO3 compositions which suggest the possibility of long range order. The refractive index and extinction coefficient were obtained by spectroscopic ellipsometry. Higher values for the refractive index are recorded due to the high polarizability of non-bridging oxygen. It is observed also that the refractive index, n increases with increasing WO3 content. It is established that there is a trend by which the energy gap decreases with increasing refractive index and increasing the polarizability of the oxide ions. The complex dielectric function ε, relative to each sample, was estimated from regression analysis. The material studied here has potential application as optical fiber.