Research On Photoelectric Properties And Application Of Bi₄Ti₃O₁₂-based Ferroelectric Materials

Ferroelectric materials have been widely used because of their dielectric,piezoelectric,pyroelectric and other characteristics,and has been a hot research area.In recent years,a special photovoltaic effect has been found in ferroelectric materials.The open circuit voltage is limited by the band gap and can be 2⁴ orders of magnitude higher.This has aroused great interest among scientific researchers.This is not only a strong photoelectric response of ferroelectric materials has unique advantages in the photovoltaic power generation,is also expected to applied in the field of photocatalysis and detection,and the need to drive,light,light light actuator-high voltage drive electric energy converter photodevice and has good application prospects.In this thesis,Bi₄Ti₃O₁₂ ferroelectric materials are selected as the research object,and the photoelectric properties of Bi₄Ti₃O₁₂ ferroelectric materials are studied from two aspects: powder and film.Firstly,A good piece of micron spherical Bi₄Ti₃O₁₂ powders was synthesized by hydrothermal method,and the affection of the hydrothermal preparation temperature on the surface of nano crystal were explored.Under the action of ultrasound,power of 100 W and the frequency of 40 KHZ,the enhancement of catalytic performance of Bi₄Ti₃O₁₂ powder under illumination was achieved.This is due to the strengthening effect of bismuth titanate with piezoelectric properties,polarization field in ultrasonic field,promote the photogenerated electron hole pair separation and migration reduces the recombination efficiency,thus improving its photocatalytic properties.In addition,Bi₄Ti₃O₁₂ ferroelectric thin films were coated successfully on FTO glass substrates by sol-gel method,the grain size of 60 nm,thickness of 150nm;the band gap is 2.97 eV,the remanent polarization Pr,saturation polarization Ps and coercive field strength Ec were 12.04 C /cm,24.40 C /cm and 104 kV/cm.The open circuit voltage in the non polarized state is 0.02 V,and the short-circuit current density is 0.18 mu A/cm2.The photoelectric response characteristics can be controlled by applying different sizes and directions bias voltage,and a reasonable explanation is given by using the Schottky theory.It is found that in negative polarization state,the open circuit voltage is increased to 0.12 V,and the short-circuit current density is increased to 0.49 A/cm2,and the photocurrent density is about 3 times higher than that of the unpolarized state.This is mainly due to the change of the internal band structure caused by ferroelectric polarization.This paper also prepared Bi₄Ti₃O₁₂/TiO2 composite film successfully through sol-gelmethod.It is found that bismuth titanate and titanium dioxide each spin coated 4layers composite film,B4T4,has optimal photoelectric response characteristic,the photocurrent density reached 4.4 A/cm2.In order to further explore the optoelectronic properties of the Bi₄Ti₃O₁₂/TiO2 composite films,B4T4 composite films were selected as the research object,studied response effect of bias and polarization state on the photoelectric response and monochromatic light.The results show that the positive bias,the negative polarization state and the intensity of monochromatic light can increase the photoelectric responsivity,and show the photovoltaic effect and the increase of the photocurrent.After polarization treatment,the open circuit voltage is increased to 0.74 V,and the short-circuit current is increased to 8.05 A/cm2.