Preparation,band Gap Modification And Properties Of Chromium-doped Barium Stannate Nanomaterials

Alkaline earth stannates ASnO₃（A=Ca,Sr and Ba）,a kind of wide band gap semiconducting perovskite oxides,have attracted increasing attention in the past decades for their outstanding properties,i.e.,high electron mobility,thermal stability and gas sensitivity.They are versatile functional perovskite materials with potentials for a range of applications such as transparent conductors,photocatalysis,perovskite solar cells,gas sensors etc.However,their intrinsic wide optical band gap（3.1–4.3 eV）limits their applications in photocatalysis,solar cells and other fields.Therefore,there is a great need to develop novel means to modify their band structures and extend their absorption to the visible light region,which further promotes the design and development of new optoelectronic devices.Theoretical calculations and experimental studies show that the band structures,optical and electrical properties of alkaline earth stannates can be easily modified by doping rare-earth or transition metal elements（i.e.,Cr,Mn,Fe and Co）.Their optical band gaps are expected to be adjusted into the visible light region.The research object carried out in this thesis is barium stannate（BaSnO₃）.The main research target is to prepare highly stable,crystalline,visible light absorption inorganic perovskite materials.The modification of optical,electrical properties and band structures of BaSnO₃ is achieved by chromium（Cr）doping,and their practical applications are also investigated.This thesis mainly includes the following two parts:（1）Preparation and photocatalytic properties of chromium-doped barium stannate BaSn_1–xCr_xO₃（BSCO-x）nanoparticles.BSCO-x nanoparticles with high crystallinity and visible light absorption were prepared by a facile peroxide-precipitate route.The formation mechanism,microstructure,morphology and optical properties of BSCO-x nanoparticles were systematically studied.The Cr doping was found to cause the reduction of the band gap（2.69–3.15 eV）.Being beneficial from the lower band gap,the Cr-doped nanoparticles could degrade methyl orange（MO）effectively under visible light irradiation.Most importantly,the BSCO-x nanopartices exhibited superior photocatalytic stability towards strong acid（pH=1）and strong alkali（pH=14）.Besides,they still had good photocatalytic activity even after second high temperature（1000°C）heat treatment.（2）Preparation and optical and electrical properties of BSCO-x films.BSCO-x thin films were deposited on fluorine-doped tin oxide（FTO）substrates via a colloidal solution spin-coating route.All the films exhibited a nanoporous structure,with the specific surface area of²0 m²/g and pore size of¹0 nm.The doping of Cr element in perovskite BSO was found to increase the crystallite size,increase the pore size,decrease slightly the surface area,reduce the optical band gap,and decrease the room temperature resistivity.Meanwhile,all the films exhibited high transparency（above70%）in 500–800 nm wavelength band,indicating the high optical quality of BSCO-x films despite their nanoporous feature.This study will extend and improve the use of perovskite BSCO-x materials with tunable band gap in varied practical applications ranging from wastewater treatment to environmentally-friendly optoelectronic or sensing devices.It is of great significance to promote the in-depth study and practical application of perovskite nanomaterials.