Structural and spectroscopic properties of SrO–As2O3–TeO2 glasses

Arsenic tellurite glass and glass ceramics doped with strontium were prepared by conventional melt quenching and heat treatment techniques with stoichiometric equation xSrO+(40-x)As₂O₃+60TeO₂: x=10 (SAT-1), 20 (SAT-2), 30 (SAT-3) mol%. The role of SrO on structural and spectroscopic features of SAT samples have been investigated. In order to generate crystalline phases having nano scale, glass samples were exposed to controlled heat treatment at 460 °C for 8hrs. X-ray diffraction (XRD) confirms non-crystalline structure for SAT glass samples whereas, crystalline phases i.e., Te₄Sr₃O₁₁, α–TeO₂, and Claudetite (As₂O₃) were identified in glass ceramic samples with crystallite size ranging from 25 to 58 nm. Structural disorder in glass matrix showed a significant role in mechanical and physical properties of glass samples at varying SrO concentration (10–30 mol%). The density decreases monotonically with increase in SrO concentration, which could be due to substitution of higher molecular weight As₂O₃ with a lower molecular weight SrO, that results in a decrease in the composition's net molecular weight. Further, thermal parameters were increased monotonically such as, glass transition temperature (T_g∼353→425°C), on-set crystalline temperature (T_õ∼378→492°C), and peak crystalline temperature (T_p∼405→506°C). Increased optical parameters were also observed with optical band gap (E_g∼2.215→3.179eV), Urbach energy (ΔΕ∼0.191→0.287eV) and refractive index (n∼2.302→2.357) while absorption edge (λ_c∼456→361A^o) was found to decrease with increase in SrO from 10 to 30mol %. The Raman and IR studies show that TeO³⁻, AsO³⁻ terminal groups are formed in the glass network through cleavage of Te–O–Te and/or As–O–As, Te–O–As linkages. AFM affirms that glass ceramic system exhibits a ripple pattern with a relief height in the order of 25–80nm. The FESEM analysis illustrates that glass ceramics contains perspicuous and haphazardly distributed nanoclusters possessing sizes in the range from 42 to 104nm.