Titanium dioxide is an inexpensive wide-gap highly ionic semiconductor with striking photocatalytic capabilities in several heterogeneous photoredox reactions. A small crystal size is desirable to maximize the surface area, since photocatalytic reactions occur at the surface of a photocatalyst. Presented here are the synthesis and microstructural characterization of 4 at.% Sc-doped TiO2 (4SDT) prepared by water-based co-precipitation. The crystal structure of 4SDT was examined via in situ high-temperature powder X-ray diffraction experiments from 25 to 1200°C. Rietveld analysis revealed single-phase anatase up to 875°C, while at 900°C the anatase-to-rutile phase transformation occurred and at higher temperatures additional reflections of Sc-rich phases (Sc2TiO5 from 975°C and Ti3Sc4O12 or Sc2O3 at 1200°C) were observed. Debye function analysis (DFA) was applied to model the total scattering pattern directly in reciprocal space, allowing the reconstruction of Ti vacancies. Both Rietveld and DFA methods were applied to estimate the nanocrystallite size and shape with consistent growth in crystallite size with temperature: an ellipsoid shape with equatorial ∼4.7 nm / axial (001) ∼6.9 nm at 25°C to equatorial ∼27.9 nm / axial (001) ∼39.6 nm at 900°C refined by Rietveld analysis, versus a cylinder shape with Da,b = 4.3 nm and size dispersion σab = 1.5 nm, Lc = 4.9 nm and σc = 2.3 nm at 25°C to Da,b = 21.4 nm, σab = 8.3 nm, Lc = 23.9 and σc = 10.9 nm at 900°C estimated by DFA. The microstructural changes obtained by Rietveld and DFA methods were supported by high-resolution transmission electron microscopy image analysis, as well as by the less direct nitrogen sorption techniques that provide information on the size of non-agglomerated and dense particles. The Ti site-occupancy factor showed a linear increase from 0.6–0.8 at 25°C to unity at 900°C for anatase, and from ∼0.7 at 900°C to unity at 1200°C for rutile, via Rietveld analysis and DFA.

中文翻译：

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Sc掺杂氧化钛纳米晶的原位高温X射线衍射研究

二氧化钛是一种廉价的宽隙高离子半导体，在几种非均相光氧化还原反应中具有惊人的光催化能力。小晶体尺寸对于最大化表面积是理想的，因为光催化反应发生在光催化剂的表面。这里介绍的是通过水基共沉淀制备的 4 at.% Sc 掺杂 TiO2 (4SDT) 的合成和微观结构表征。通过 25 至 1200°C 的原位高温粉末 X 射线衍射实验检查了 4SDT 的晶体结构。Rietveld 分析显示单相锐钛矿温度高达 875°C，而在 900°C 时发生锐钛矿到金红石的相变，并且在较高温度下富钪相（Sc2TiO5 来自 975°C 和 Ti3Sc4O12 或 Sc2O3 在 1200 °C) 进行观察。德拜函数分析 (DFA) 用于直接在倒易空间中对总散射模式进行建模，从而可以重建 Ti 空位。应用 Rietveld 和 DFA 方法来估计纳米微晶尺寸和形状，微晶尺寸随温度的一致增长：椭圆体形状，赤道约 4.7 nm/轴（001）约 6.9 nm，25°C 至赤道约 27.9 nm/轴(001) 通过 Rietveld 分析在 900°C 下精制约 39.6 nm，与 Da,b = 4.3 nm 和尺寸色散 σab = 1.5 nm、Lc = 4.9 nm 和 σc = 2.3 nm 的圆柱形状相比，在 25°C 至 Da， b = 21.4 nm，σab = 8.3 nm，Lc = 23.9 和 σc = 10.9 nm，在 900°C 下由 DFA 估计。Rietveld 和 DFA 方法获得的微观结构变化得到高分辨率透射电子显微镜图像分析的支持，以及通过较少直接的氮吸附技术，提供关于非附聚和致密颗粒尺寸的信息。通过 Rietveld 分析和 DFA，Ti 位点占有系数从 25°C 的 0.6-0.8 线性增加到 900°C 的锐钛矿，从 900°C 的~0.7 到 1200°C 的金红石。