Key Laboratory of Polar Materials and Devices, Ministry of Education, East China Normal University, Shanghai, 200241, People's Republic of China.
Dalton Trans. 2011 Aug 21;40(31):7967-75. doi: 10.1039/c1dt10443h. Epub 2011 Jul 8.
Ferroelectric lanthanum (La)-substituted bismuth titanate (Bi(4-x)La(x)Ti(3)O(12), BLT) nanocrystalline films with the composition range of 0 ≤x≤ 1 have been directly deposited on n-type Si (100) substrates by chemical solution deposition. The La substitution effects on the preferred orientation, surface morphology, phonon modes, emission bands and electronic band structures of the BLT films have been investigated by microscopy, Raman scattering, photoluminescence and spectroscopic ellipsometry at room temperature. X-Ray diffraction analysis shows that the films are polycrystalline and exhibit the pure perovskite phase structure. With increasing La composition, the (100)-orientation degree can be enhanced and the root-mean-square roughnesses slightly increase from 6.5 to 8.3 nm. It was found that the Raman-active mode A(1g)[Bi] at about 59 cm(-1) is unchanged while the B(1g) and A(1g)[Ti] phonon modes at about 648 and 853 cm(-1) are shifted towards higher frequency by about 36.6 and 8.4 cm(-1), respectively. Photoluminescence spectra show that the intensity of the peak located at about 2.3 eV increases with the La composition, except for the Bi(3)LaTi(3)O(12) film, due to the smallest grain size and oxygen vacancy defects. The optical constants of the BLT films have been uniquely extracted by fitting the measured ellipsometric spectra with a four-phase layered model (air/surface rough layer/BLT/Si) in the photon energy range of 0.73-4.77 eV. The Adachi dielectric function model has been successfully applied and reasonably describes the optical response behavior of the ferroelectric BLT films. Moreover, the film packing density decreases while the optical band gap linearly increases from 3.610 ± 0.066 to 3.758 ± 0.068 eV with increasing La composition. It is surmised that the phenomena are mainly ascribed to the variations of the electronic structure, especially for the conduction band, which is perturbed by the La doping.
掺镧铋钛酸钡（Bi(4-x)La(x)Ti(3)O(12)，BLT）纳米晶薄膜具有 x 取值范围为 0 ≤x≤ 1 的铁电特性，通过化学溶液沉积法直接沉积在 n 型 Si（100）衬底上。采用显微镜、室温下的喇曼散射、光致发光和光谱椭圆偏振法研究了 La 取代对 BLT 薄膜的择优取向、表面形貌、声子模式、发射带和电子能带结构的影响。X 射线衍射分析表明，薄膜为多晶，具有纯钙钛矿相结构。随着 La 组成的增加，（100）取向度可以增强，均方根粗糙度从 6.5nm 略微增加到 8.3nm。发现约 59cm(-1)处的 Raman 活性模 A(1g)[Bi]不变，而约 648cm(-1)和 853cm(-1)处的 B(1g)和 A(1g)[Ti]声子模分别向高频移动约 36.6 和 8.4cm(-1)。光致发光光谱表明，除了晶粒尺寸最小和氧空位缺陷的 Bi(3)LaTi(3)O(12)薄膜外，位于约 2.3eV 的峰强度随着 La 组成的增加而增加。通过在光子能量范围为 0.73-4.77eV 内，用空气/表面粗糙层/BLT/Si 四层模型拟合测量的椭圆偏振光谱，唯一地提取了 BLT 薄膜的光学常数。成功应用了 Adachi 介电函数模型，并合理描述了铁电 BLT 薄膜的光学响应行为。此外，随着 La 组成的增加，薄膜堆积密度减小，而光学带隙从 3.610±0.066eV 线性增加到 3.758±0.068eV。据推测，这些现象主要归因于电子结构的变化，特别是对于受 La 掺杂影响的导带。
