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Local Structural Distortions and Failure of the Surface-Stress “Core–Shell” Model in Brookite Titania Nanorods
Chemistry of Materials ( IF 8.6 ) Pub Date : 2019-12-30 , DOI: 10.1021/acs.chemmater.9b03762
Victor Krayzman 1 , Eric Cockayne 1 , Aaron C. Johnston-Peck 1 , Gavin Vaughan 2 , Fan Zhang 1 , Andrew J. Allen 1 , Larissa Y. Kunz 3 , Matteo Cargnello 3 , Lawrence H. Friedman 1 , Igor Levin 1
Affiliation  

Structural refinements of whole-nanoparticle atomistic models using X-ray total-scattering data and the reverse Monte Carlo algorithm were demonstrated for mixtures of TiO2 brookite nanorods and irregularly shaped anatase nanoparticles, which exhibit enhanced photocatalytic properties. The brookite and anatase nanocrystals were shown to undergo lattice-volume expansion and contraction relative to their bulk prototypes. Detailed analysis of the refined structures focused on the nanorods because of their well-defined shapes and habits; the soundness of the obtained characteristics was assessed using first-principles calculations. The atomic positions in the nanorods differed from the bulk structure by an effective shift of the Ti Wyckoff position in the brookite unit cell, combined with additional static atomic displacements that increased progressively from the nanorod axis toward its side surfaces. A similar radial gradient was observed for distortions of the [TiO6] octahedra. A cross-sectional pattern of structural relaxations exhibited symmetry consistent with that imposed by the nanorod habits. Density functional theory calculations were in qualitative agreement with the experimental observations and additionally revealed a strong dependence of the structural relaxations, including lattice-volume changes, on sorbate coverage. The experimental and computed magnitudes of these relaxations appeared to be significantly larger than those predicted by a simple surface-stress model, with the difference attributed to a complex gradient of the local electrostatic potential within the nanorods. This study demonstrates the potential of using RMC refinements to obtain a detailed picture of atomic order in nanoparticles and highlights the existence of complex, spatially variable distortions that need to be considered while interpreting the electronic properties of these materials.

中文翻译:

Brookite Titania纳米棒中的局部结构变形和表面应力“核-壳”模型的破坏

利用X射线总散射数据和反向蒙特卡洛算法对TiO 2混合物进行了全纳米粒子原子模型的结构优化板钛矿纳米棒和不规则形状的锐钛矿型纳米颗粒,具有增强的光催化性能。板钛矿和锐钛矿型纳米晶体显示出相对于其本体原型而言晶格体积膨胀和收缩。由于纳米棒具有明确的形状和习惯,因此对精制结构的详细分析集中在纳米棒上。使用第一性原理计算评估获得的特性的可靠性。纳米棒中的原子位置与块状结构的不同之处在于板钛矿晶胞中Ti Wyckoff位置的有效偏移,再加上从纳米棒轴向其侧面逐渐增加的其他静态原子位移。对于[TiO 6]的变形,观察到了类似的径向梯度]八面体。结构弛豫的横截面图案显示出与纳米棒习惯所施加的对称性一致的对称性。密度泛函理论计算与实验观察在质量上吻合,并且还揭示了结构弛豫(包括晶格体积变化)对山梨酸盐覆盖率的强烈依赖性。实验和计算得出的这些弛豫幅度似乎比简单表面应力模型所预测的幅度大得多,其差异归因于纳米棒内局部静电势的复杂梯度。这项研究证明了使用RMC精炼技术获得纳米粒子中原子序的详细图片的潜力,并强调了复合物的存在,
更新日期:2019-12-31
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