The Fabrication And Properties Of Perovskite Oxynitride BaTaO₂N Epitaxial Thin Film

Photocatalytic water splitting,which can produce hydrogen and oxygen from water utilizing solar energy via the semiconductor photovoltaic effect,will realize the ingenious conversion of solar energy to hydrogen energy.It is expected to solve the energy crisis and environmental pollution.The perovskite oxynitride BaTaO2N,which has ideal conduction and valence band positions,is considered to be a suitable material for photocatalytic water splitting.However,the efficiency of BaTaO2N has been far lower than its theoretical value,indicating that there may be physical defects in the material itself.In theory,photocatalytic water splitting involves three steps:photon absorption,carrier transport and surface reaction.The basic physical properties of the semiconductor related to these steps include refractive index,absorption coefficient,band gap,conduction and valence band positions,carrier concentration,carrier mobility,nonequilibrium carrier lifetime and surface state.The fabrication of single crystal films and measurement of their basic physical properties are the direct and effective means to study the factors affecting the photocatalytic properties of materials.In this dissertation,we focus on the study of BaTaO2N epitaxial thin films.The main contents are as followThe BaTaO2N films were grown on the MgO(100)and SrRuO3/SrTiO3(100)substrates by pulsed laser deposition.The analyses of microstructure and elemental composition indicated that BaTaO2N films were epitaxial growth with many defects and dislocations.The physical parameters of BaTaO2N films were measured,such as absorption spectrum,optical constant spectrum,dielectric constant and dielectric loss spectra and the absorption coefficient was calculated from the optical extinction coefficient.The absorption edge of BaTaO2N/MgO(100)films redshifted to 600nm after annealing at high temperature.At the same time,the film recrystallized and became granular film,accompanied by the precipitation of Ta3N5 and BaTa2O6 impurities.After annealing,the film is no longer suitable for the determination of physical parameters.