Influence of nano crystalline behavior of Nb2O5 – Sb2O3 – TeO2 glass ceramics on structural and thermal studies

Abstract

xNb2O5–(25-x)Sb2O3–75TeO2 (Where x = 5,10,15,20 mol% of Nb2O5) glass system have been successfully prepared by using conventional melt-quenching route. Nano clusters and crystalline phases are obtained with the employment of heat treatment (HT) procedure executed at various temperatures depending upon composition. These samples are characterized using XRD, SEM, DTA, IR and RAMAN studies. X-ray diffraction (XRD) have been done for both glass and glass ceramics to confirm the crystalline and amorphous nature of the samples respectively. XRD patterns of glass ceramic samples exhibit various structural changes such as Sb2Te2O9, Nb2Te4O13, Nb2Te3O11, Senarmontite (α-Sb2O3), Valentinite (β-Sb2O3), γ, α -TeO2, Sb6O13 and Nb0.5O4Sb1.5 associated with the glass ceramics. From XRD, it is clear that the antimony and tellurium ions co-exist in mixed valence states (Sb5+, Sb3+ and Te4+, Te6+)in host matrix of glass ceramics. Nano crystalline clusters are identified by using scanning electron microscopy (SEM) and are found to be in the range of size approximately 149.1–193.6 nm. The percentage of various elements associated with the glass ceramics is discussed by the EDX analysis. The thermal parameters such as glass transition temperature (Tg) and onset crystalline temperature (To) are determined from DTA spectra for all the samples. As Nb2O5 content is increased, the values of glass transition temperature are found to be increased from 329 °C to 418 °C (Tg) and 467 °C to 531 °C (To) for glasses and glass ceramics for 262 °C to 385 °C (Tg), 431 °C to 493 °C (To) respectively. IR and Raman studies reveals that the presence of various structural units such as [TeO4]tbp, [TeO3]tp, [TeO3+1] and TeO6 are interconnected with SbO6, NbO6 and NbO4 units associated with glass and glass ceramic host matrix. The optical absorption spectra have been studied for the samples and data is correlated with the DSC spectra.