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Structure of molten titanium dioxide

机译：熔融二氧化钛的结构

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摘要

The x-ray structure factor of molten TiO_2 has been measured, enabled by the use of aerodynamic levitation and laser beam heating, to a temperature of T = 2250(30) K. The Ti-O coordination number in the melt is close to n_(Tio) = 5.0(2), with modal Ti-O bond length r_(Tio) = 1.881(5) A, both values being significantly smaller than for the high temperature stable rutile crystal structure (n_(Tio) = 6.0, r_(Tio) = 1.959 A). The structural differences between melt and crystal are qualitatively similar to those for alumina, which is rationalized in terms of the similar field strengths of Ti~(4+) and Al~(3+). The diffraction data are used to generate physically and chemically reasonable structural models, which are then compared to the predictions based on various classical molecular dynamics (MD) potentials. Interatomic potentials, suitable for modeling molten TiO_2, are introduced, given the inability of existing MD models to reproduce the diffraction data. These potentials have the additional advantage of being able to predict the density and thermal expansion of the melt, as well as solid amorphous TiO_2, in agreement with published results. This is of critical importance given the strong correlation between density and structural parameters such as n_(Tio). The large thermal expansion of the melt is associated with weakly temperature dependent structural changes, whereby simulations show that n_(Tio) = 5.85(2) - [3.0(1) × 10~(-4)]T(K, 2.75 Acutoff). The TiO_2 liquid is structurally analogous to the geophysically relevant high pressure liquid silica system at around 27 GPa. We argue that the predominance of fivefold polyhedra in the melt implies the existence of as-yet-undiscovered TiO_2 polymorphs, based on lower-than-octahedral coordination numbers, which are likely to be metastable under ambient conditions. Given the industrial importance of titanium oxides, experimental and computational searches for such polymorphs are well warranted.
机译：测量了熔融的TiO_2的X射线结构因子，通过使用空气悬浮和激光束加热使之达到T = 2250（30）K。熔体中的Ti-O配位数接近n_ （Tio）= 5.0（2），模态Ti-O键长r_（Tio）= 1.881（5）A，两个值均明显小于高温稳定的金红石晶体结构（n_（Tio）= 6.0，r_ （Tio）= 1.959 A）。熔体和晶体之间的结构差异在质量上与氧化铝相似，这在Ti〜（4+）和Al〜（3+）的相似场强方面是合理的。衍射数据用于生成物理和化学上合理的结构模型，然后将其与基于各种经典分子动力学（MD）势的预测结果进行比较。鉴于现有的MD模型无法重现衍射数据，引入了适合建模熔融TiO_2的原子间电势。这些潜力还具有能够预测熔体以及固体无定形TiO_2的密度和热膨胀的其他优点，与已公开的结果一致。鉴于密度和结构参数（例如n_（Tio））之间的强烈相关性，这一点至关重要。熔体的大热膨胀与温度依赖性较小的结构变化有关，由此模拟表明n_（Tio）= 5.85（2）-[3.0（1）×10〜（-4）] T（K，2.75 Acutoff） 。 TiO_2液体在结构上类似于大约27 GPa的与地球物理相关的高压液体二氧化硅系统。我们认为，熔融态中五面体的优势暗示着，基于低于八面体的配位数，尚未发现的TiO_2多晶型物的存在，在环境条件下可能是亚稳态的。考虑到钛氧化物的工业重要性，对此类多晶型物进行实验和计算研究是非常有必要的。

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  • 来源
    《Physical review》 |2014年第9期|094204.1-094204.13|共13页
  • 作者

    O. L. G. Alderman; L.B. Skinner; C. J. Benmore; A. Tamalonis; J. K. R. Weber;

  • 作者单位

    Materials Development, Inc., Arlington Heights, Illinois 60004, USA,X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA;

    Materials Development, Inc., Arlington Heights, Illinois 60004, USA,X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA,Mineral Physics Institute, Stony Brook University, Stony Brook, New York 11794-2100, USA;

    X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA;

    Materials Development, Inc., Arlington Heights, Illinois 60004, USA;

    Materials Development, Inc., Arlington Heights, Illinois 60004, USA,X-Ray Science Division, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA;

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  • 正文语种 eng
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  • 关键词

    disordered solids; computer simulation of liquid structure;

    机译：无序固体液体结构的计算机模拟;

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