Energy band structure and optical band gap calculations of AgSbO₃ photo-catalystic pyrochlore crystal phase embedded in Ag₂O doped sodium antimonate glass ceramics

Our earlier studies (that include several characterization studies viz., XRD, XPS, SEM, TEM, DSC, spectroscopy, positron annihilation and dielectric studies) of Ag₂O doped Na₂O–Sb₂O₃ glass ceramics indicated that the glass ceramic containing 0.1 mol% of Ag₂O is embedded with larger concentration of AgSbO₃ crystal grains and such ceramic is found to be highly electrical resistant and possess larger free volume space. Moreover, AgSbO₃ pyrochlore crystal phase has got plenty of ferroelectric and piezoelectric applications. In continuation to the earlier studies, the present investigation is focused on evaluation of band structure and energy band gap calculations of AgSbO₃ pyrochlore crystal phase entrenched in the glass ceramic. The glasses of the composition 40Na₂O–60Sb₂O₃ with 0.1 mol% of Ag₂O were ceramicized by subjecting them for different time intervals (24–100 h) of heat treatment at 830 °C. XRD and XPS techniques were used to characterize samples. The results of these studies indicated the predominant presence of AgSbO₃ pyrochlore crystal phase in the samples heat treated for 100 h. The calculations of the structural and electronic properties of defective pyrochlore AgSbO₃ crystal phase were performed using the CASTEP program with the local density approximation. The calculated lattice constant is turned out to be 10.16978 Å and the indirect band gap is estimated to be 0.227 eV. The value of this band gap is found to be far below from the experimental value. The reasons for such low value have been identified and discussed.