Study On Spontaneous Polarization Control For The Photoelectric Properties Of Barium Titanate-based Ferroelectric Materials

Ferroelectric materials have an abnormal p hotovoltaic effect and a high open circuit voltage that is not limited by the band gap,and have high research value in solar energy utilization.The manufacturing process of ferroelectric nanomaterials is simpler than that of bulk materials or inorganic f erroelectric ceramics,and the photoelectric properties are excellent,and the required external polarization electric field is relatively low.Cadmium sulfide is a very potential inorganic photocatalyst for water splitting due to its small optical band ga p（～2.4 e V）and suitable energy band position.However,the severe photocorrosion in the catalytic process restricts its large-scale application.At the same time,cadmium sulfide is very toxic,and it will pose a huge threat to aquatic organisms after ent ering the water body,which also limits its further development.Therefore,it is of great practical significance to improve the light absorption performance and electron transmission capacity of traditional ferroelectric materials,to stabilize cadmium su lfide to prevent it from severe photo-corrosion or to find effective substitutes.In this paper,a new core-shell structure of crystalline BaTiO ₃/amorphous BaTiO_3-x/crystalline CdS composite nanoparticles was prepared by hydrothermal method,aluminum reduction method and chemical bath deposition method,using X-ray diffraction,scanning electron microscope,The composite nanoparticles were characterized by ray energy dispersion spectroscopy and transmission electron microscopy,and the proportions of their crystal structure,surface morphology and chemical composition were confirmed.The UV-Vis-NIR diffuse reflectance spectroscopy test results of the composite nanoparticles confirmed the red shift of the visible light absorption edge caused by oxygen deficie ncy in BaTiO_3-x.The nanopowder was directly coated on the indium tin oxide（ITO）glass substrate to make a photoelectrode and the photoelectrochemical test was carried out.The results showed that:the photogenerated current density of the composite heterojunction film without external electric field polarization（J_p）It is 100（?）A/cm²,and when a polarizing electric field of 18.8 k V/cm is applied,J_p reaches about 200（?）A/cm².Due to effective electron-hole separation and enhanced visible light absorption,there is a good synergy between ferroelectrics and semiconductors.At the same time,the photocurrent value is 10 times that of the pure CdS film under the same conditions.The photocatalytic hydrogen production test results of the composite heterojunction nanoparticles and cadmium sulfide monomer show that the hydrogen yield of the composite heterojunction is 40%higher than that of the monomer cadmium sulfide under the same conditions,and the UV-Vis-NIR diffuse reflectance spectroscopy test results of the composite heterojunction before and after the catalytic reaction show that the optical band gap is basically unchanged,confirming that the construction of a composite heterojunction can effectively prevent the photochemical corrosion of cadmium sulfide.The long-period photoelectrochemical test results show that the photoelectric response current of the composite heterojunction film decreases very weakly within the continuous light test time of45 min,which also confirms that the composite heterojunctio n structure has good photoelectrochemical stability.A composite heterojunction was constructed with graphite phase carbon nitride instead of cadmium sulfide and black barium titanate.The photoelectrochemical characterization of composite heterojunction nanoparticles and corresponding monomers and the photocatalytic degradation test of bisphenol A were carried out.The results show that the J_p of g-C₃N₄（11.5（?）A/cm²）is nearly 2 times higher than that of BaTiO ₃（6（?）A/cm²）,indicating that a narrower band gap is conducive to the enhancement of light absorption,leading to an increase in the concentration of photogenerated carriers and more production.Big J_p.The J_p of the BaTiO₃/BaTiO_3-x/g-C₃N₄ composite film reaches 135（?）A/cm²,which is about 11 times that of g-C₃N₄.That proves the heterojunction structure formed by g-C₃N₄ and BaTiO₃/BaTiO_3-x has a good synergy.This effect expands the solar absorption range and effectively promotes the separation of photogenerated electron-hole pairs.Under visible light irradiation,BaTiO ₃/BaTiO_3-x/g-C₃N₄ can effectively catalyze the degradation of bisphenol A dye under acidic or weakly alkaline conditions（degradatio n of more than 30%）;under weakly acidic conditions with a p H of 4-6,The decomposition rate is more than 55%.The composite heterojunction promotes the separation of photogenerated carriers in the sample and the expansion of the visible light absorption r ange,which can significantly enhance the degradation rate and photocurrent intensity,further indicating that the spontaneous polarization control of the photoelectric properties of ferroelectric materials is feasible.