【作者】 武峥；

【导师】 张以河；

【作者基本信息】 中国地质大学（北京） ， 环境科学与工程， 2014， 博士

【摘要】 铁电材料的光伏效应开路电压可达几千伏特，远优于传统的半导体p-n结光伏材料。传统铁电材料禁带宽度大(>3.3eV)，因此其光伏光催化对应紫外光响应波段。而太阳光中紫外光仅占4%，可见光约占43%，因此发展可见光响应的新型铁电光伏材料是十分重要的。多铁材料通常是指一种具有磁性的特殊铁电材料。近年来发展的一些室温铁酸盐多铁材料如BiFeO3等，禁带宽度约为2~3eV，有望实现良好的可见光光伏及光催化效应，可用于太阳光分解水制氢和降解有机污染废水溶液，在环保领域具有很好的应用前景。本论文较系统地研究了铁酸盐多铁陶瓷及纳米材料的制备工艺、光伏和光催化性能，并分析了其物理机理。采用固相反应高温烧结法分别制备了铁酸盐多铁Pb(Fe1/2V1/2)O3陶瓷，并采用溶胶凝胶法制备了铁酸锌、铁酸镧和铁酸铋薄膜。研究了它们的可见光光伏性能。在多铁陶瓷Pb(Fe1/2V1/2)O3陶瓷中，诱导的光电流几乎是和外加光强成正比例，测得的可见光光伏开路电压输出达0.7V，远高于目前报道的铁酸铋材料(0.3V)。制备的多铁薄膜均表现出明显的可见光光伏性能，但是零偏置光电流几乎为零，这可能是因为缺陷浓度较高所致。通过分析对比半导体光伏、铁电/多铁材料光伏、高漏电多铁材料光伏三种类型材料的光伏物理机制，发现其光伏效应分别决定于界面能垒（界面效应）、铁电极化强度（体效应）及电场下缺陷定向迁移造成的带电缺陷浓度梯度。设计了相应的等效电路；并利用应变调控，使p-n结材料的光伏开路电压提高了约12%，光伏转化效率提高了约9.1%。采用水热法分别制备了BiFeO3、CuFe2O4、ZnFe2O4三种铁酸盐多铁纳米材料。实验表明均对罗丹明B溶液具有很好的光催化降解效果，降解效率分别达到99%、91%和95%；对质量浓度为10mg/L的罗丹明B溶液，最佳的催化剂用量分别为6g/L、1g/L和2g/L。采用水热法制备了多铁BiFeO3纳米棒，利用多铁材料压电特性，实现了机械催化效应。对罗丹明B溶液，其机械催化降解率达90%以上。进一步，利用机械催化和光催化效应联合，获得了提高的催化降解率。更多还原

【Abstract】 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.更多还原