Key Laboratory of Polar Materials and Devices, Ministry of Education, Department of Electronic Engineering, East China Normal University, Shanghai 200241, China.
ACS Appl Mater Interfaces. 2013 Apr 24;5(8):3191-8. doi: 10.1021/am400196c. Epub 2013 Apr 15.
The optical and ferroelectric properties of (Na0.5Bi0.5)1-xCex(Ti0.99Fe0.01)O3 (NBCTFx; 0 ≤ x ≤ 0.10) nanocrystalline films deposited on platinized silicon (Pt/TiO2/SiO2/Si) substrates using a sol-gel method were investigated. The microstructure, surface, and cross-sectional morphology and compositions of the films were analyzed by X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy, respectively. The X-ray diffraction patterns indicate that all films are polycrystalline and show the single perovskite structure. The dielectric functions of the NBCTFx films can be uniquely extracted by fitting the measured ellipsometric spectra with a four-phase-layered model (air/surface rough layer/NBCTFx/Pt) in the photon energy range of 0.6-6.4 eV. The Tauc-Lorentz model was successfully applied and reasonably describes the spectral response behavior of ferroelectric NBCTFx films in the light-frequency region. It was found that the optical band gap and grain size decrease with increasing cerium composition because of the introduction of disorder and defects. The electrical results show that the leakage current density of the films was decreased with increasing cerium composition by reducing the density of oxygen vacancies and forming the defect complexes. The optimal ferroelectric properties were obtained in the film doped with x = 0.10, whose remnant polarization and coercive field values are 14.9 μC/cm(2) and 217.3 kV/cm, respectively. The present results could be crucial for future applications of lead-free ferroelectric and optoelectronic devices.
采用溶胶-凝胶法在镀铂硅（Pt/TiO2/SiO2/Si）衬底上沉积（Na0.5Bi0.5）1-xCex（Ti0.99Fe0.01）O3（NBCTFx；0 ≤ x ≤ 0.10）纳米晶薄膜，研究了其光学和铁电性能。利用 X 射线衍射、扫描电子显微镜和 X 射线光电子能谱分别分析了薄膜的微观结构、表面、横截面形貌和组成。X 射线衍射图谱表明，所有薄膜均为多晶，呈现单一钙钛矿结构。在光子能量范围为 0.6-6.4 eV 时，用四相层模型（空气/表面粗糙层/NBCTFx/Pt）拟合测量的椭圆偏振光谱，可以唯一提取出 NBCTFx 薄膜的介电函数。Tauc-Lorentz 模型成功应用并合理描述了铁电 NBCTFx 薄膜在光频区域的光谱响应行为。研究发现，由于无序和缺陷的引入，随着铈组成的增加，光学带隙和晶粒尺寸减小。电结果表明，通过减少氧空位密度并形成缺陷复合物，薄膜的漏电流密度随铈组成的增加而降低。在掺杂 x = 0.10 的薄膜中获得了最佳的铁电性能，其剩余极化和矫顽场值分别为 14.9 μC/cm2和 217.3 kV/cm。这些结果对于未来无铅铁电和光电设备的应用可能至关重要。
