Impact of Annealing of BaSnO₃ in Forming Gas on Its Optoelectronic Properties

Annealing of BaSnO₃ single crystals and films in inert and reducing atmospheres, such as Ar, N₂, and H₂S, has been proven to enhance their optoelectronic properties due to altering the thermodynamic feasibility of oxygen vacancy formation and incorporation of foreign elements. However, the impact of annealing on the thermodynamic feasibility of oxygen vacancy defects and extrinsic defects (due to the presence of foreign elements) in polycrystalline BaSnO₃ has yet to be explored.<br/>This work BaSnO₃ pellets synthesized by solid-state reaction, annealed in the temperature range 600 °C to 1000 °C, for varying durations from 10 minutes to 12 hours, under air, vacuum, Ar, and forming gas. In all the samples, the O1s spectra, as investigated by XPS analysis, show peaks corresponding to the oxygen lattice site (O_L) and oxygen vacancy (O_V). All pellets exhibit conductivity regardless of the annealing environment. However, a significant difference is seen in the pellets annealed in forming gas: they show enhanced conductivity and turn black. This colour change is not due to free charge carrier absorption, as confirmed by UV-DRS analysis of samples from all annealing environments. We investigate the reason behind this phenomenon. While the formation of Sn along with the BaSnO₃ phase is already reported during annealing in forming gas above 900 °C, it is suggested that the presence of hydrogen, evidenced by CHNS elemental analysis, might play a role before 900 °C. Hydrogen is most probably incorporated in the interstitial sites of the BaSnO₃ lattice. The H-interstitial is compensated by conduction band electrons.<br/>The study investigates the interplay of defects and their effects on optoelectronic properties through comprehensive optical characterization using UV-DRS and electrical characterization via variable temperature Hall measurements.