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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >Evolution of orientation degree, lattice dynamics and electronic band structure properties in nanocrystalline lanthanum-doped bismuth titanate ferroelectric films by chemical solution deposition
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Evolution of orientation degree, lattice dynamics and electronic band structure properties in nanocrystalline lanthanum-doped bismuth titanate ferroelectric films by chemical solution deposition

机译：化学溶液沉积法制备纳米晶镧掺杂钛酸铋铁电薄膜的取向度，晶格动力学和电子能带结构性质

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摘要

Ferroelectric lanthanum (La)-substituted bismuth titanate (Bi _(4-x)La_xTi_3O_(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_3LaTi_3O _(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.
机译：组成范围为0≤x≤1的铁电镧（La）取代钛酸铋（Bi _（4-x）La_xTi_3O_（12），BLT）纳米晶膜已通过以下方法直接沉积在n型Si（100）衬底上化学溶液沉积。在室温下，通过显微镜，拉曼散射，光致发光和光谱椭圆光度法研究了La取代对BLT膜的优选取向，表面形态，声子模式，发射带和电子能带结构的影响。 X射线衍射分析表明该膜是多晶的，并表现出纯的钙钛矿相结构。随着La组成的增加，（100）取向度可以提高，并且均方根粗糙度从6.5 nm略微增加到8.3 nm。发现在大约59 cm〜（-1）处的拉曼激活模式A_（1g）[Bi]不变，而在大约648和853 cm〜处的B_（1g）和A_（1g）[Ti]声子模式。 （-1）分别向高频移动约36.6和8.4 cm〜（-1）。光致发光光谱表明，由于Bi尺寸最小和氧空位缺陷，除了Bi_3LaTi_3O_（12）膜外，随La组成，位于约2.3 eV处的峰强度增加。通过将测得的椭圆光谱与四相分层模型（空气/表面粗糙层/ BLT / Si）拟合，光子能量范围为0.73-4.77 eV，可以唯一地提取BLT膜的光学常数。 Adachi介电函数模型已成功应用，并合理地描述了铁电BLT薄膜的光学响应行为。而且，随着La组成的增加，膜堆积密度降低，而光学带隙从3.610±0.066线性增加到3.758±0.068eV。据推测，该现象主要归因于电子结构的变化，特别是对于导带，其受到La掺杂的干扰。

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