Research Of Photovoltaic And Catalytic Performance Of Multiferroic Ferrite Materials

Recently the photovoltaic effect in ferroelectric materials has attractedconsiderable interest. The open-circuit photo-voltage of ferroelectric materials can be upto several kV, which is much higher than that of traditional semiconductive p-n junctionphotovoltaic materials. In general, the band gap energy of traditional ferroelectricmaterials is very high (>3.3eV), which corresponds to the ultraviolet light. However,ultraviolet light accounts for only a small fraction (4%) of the sun’s energy compared tovisible light (43%). Then it is in urgent need of new ferroelectric photovoltaic materialswith low band gap energy to respond to visible light. Multiferroic materials aregenerally referred to the typical magnetic ferroelectric materials. Some multiferroicferrite materials developed in recent years such as BiFeO3, possess the low band gapenergy of2-3eV, which corresponds to the visible-light wavelength range. Then it ispossible to achieve the excellent visible-light photovoltaic and photocatalytic effect. Thevisible-light photovoltaic and photocatalytic effect of multiferroic materials can berespectively used in solar light splitting water for hydrogen clean energy production anddecomposing organic dye wastewaster, which make it hopeful for application in thefield of environmental science. In this work, the fabrication of multiferroic ferritematerials and their visible-light photovoltaic and photocatalytic performance isinvestigated. The main works in this dissertation are as following:The multiferroic ferrite Pb(Fe1/2V1/2)O3ceramic and BiFeO3, LaFeO3and ZnFe2O4films were synthesized through solid phase reaction sintering method and sol-gelmethod, respectively. The visible-light photovoltaic performance was characterized. Thephoto-excited electric current of Pb(Fe1/2V1/2)O3ceramic is almost proportional to theincident light illumination intensity. The open-circuit photo-voltage of Pb(Fe1/2V1/2)O3ceramic was up to~0.7V, which was much higher than the value (~0.3V) in BiFeO3film. These multiferroic films also behavior the obvious visible-light photovoltaic effect.However, the zero-bias photocurrent of multiferroic films is almost equal to zero, whichmay originate from the high defect concentration in the multiferroic ferrite films. Thedependence of environmental humidity on the surface electric properties of LaFeO3andZnFe2O4films. With the increase of humidity from10%to90%, the capacitance increases, while the electrical impedance decrease. The photovoltaic effects ofsemidocnducive p-n junction, ferroelectric/multiferroic materials, and typicalhigh-leakage multiferroic materials are compared and analyzed. Their physicalmechanisms are different. The photovoltaic effect of semidocnducive p-n junction isdependent on the p-n interface energy barriers and only occurs in the thin interface layer.The photovoltaic effect of ferroic/multiferroic materials is originated from theferroelectric remanent polarization strength and can occur in the whole bulk material.The photovoltaic effects of typical high-leakage multiferroic materials may be due tothe occurrence of defect concentration gradient distribution under the external electricfields. The equivalent circuits for the three photovoltaic effects were plotted in this work.Furthermore, by utilizing a magnetostrictive strain to modulate the energy bandgap ofsemiconductive Si p-n junction, the open-circuit voltage and the maximum photovoltaicoutput power of the Si solar cell could be enhanced by~12%and~9.1%, respectively.The ferrite BiFeO3, CuFe2O4and ZnFe2O4powders were synthesized throughhydrothermal reaction. It was found that these powders possessed excellent visible-lightphotocatalytic performance and could be used to degradate Rhodamine B dyewastewater solutions. The photocatalytic degradation ratios of BiFeO3, CuFe2O4andZnFe2O4powders are up to99%,91%and95%, respectively. The optimizedphotocatalytic additional masses of BiFeO3, CuFe2O4and ZnFe2O4powders todegradate Rhodamine B solution of10mg/L are6g/L,1g/L and2g/L, respectively.The multiferroic ferrite BiFeO3nanobars were synthesized through hydrothermalreaction method. The mechano-catalytic effect was realized via the product ofpiezoelectric effect and electro-chemically catalytic effect. For Rhodamine B dyesolution, the mechano-catalytic ratio of BiFeO3nanobars can be up to~90%. Furtherly,the enhanced catalytic degradation ratio could be achieved by combining photocatalyicand mechano-catalytic effects.