Abstract

Solid state phase transformations have drawn great attention because they can be effectively exploited to control the microstructure and property of materials. Understanding the physics of such phase transformation processes is critical to designing materials with controlled structure and with desired properties. However, in traditional ex situ experiments, it is hard to achieve position controlled phase transformations or obtain desirable crystal phase on nanometer scale. Meanwhile the underlying mechanisms of the reaction processes are not fully understood due to the lack of direct and real-time observation. In this paper, we observe phase transformation from body-centered tetragonal PX-PbTiO₃ to monoclinic TiO₂(B) on the atomic scale by in situ electron irradiation during heat treatment in transmission electron microscope, at pre-defined locations on the sample. We demonstrate that by controlling the location of the incident electron beam, a porous TiO₂(B) crystal structure can be formed at the desired area on the nanowire, which is difficult to achieve by traditional synthesis methods. Upon in situ heating, the Pb atoms in the crystal migrate out of the pristine nanowire through inelastic scattering under incident electrons while high temperature(> 400 °C) provides energy for the crystallization of TiO₂(B) and the volatilization of a substantial number of Pb atoms, which makes the resultingTiO₂(B) nanowires to be porous. In contrast, at temperatures 400 °C, the segregated Pb atoms form Pb particles and the TiO_x nanowires remain in the amorphous state. This work not only provides in situ visualization of the phase transition from the PX-PbTiO₃ to monoclinic TiO₂(B), but also suggests a crystallography engineering strategy to obtain the desired crystal phase at controlled locations on the nanometer scale.

中文翻译：

---

通过原位电子辐照控制纳米线中的相变

摘要

固态相变引起人们极大的关注，因为可以有效地利用它们来控制材料的微观结构和性能。了解这种相变过程的物理原理对于设计具有受控结构和所需特性的材料至关重要。然而，在传统的异位实验中，难以实现位置控制的相变或难以获得纳米级的所需晶相。同时，由于缺乏直接和实时的观察，尚未完全理解反应过程的潜在机理。在本文中，我们观察了从体心四方PX-PbTiO ₃到原子尺度上单斜相TiO ₂（B）的相变，在透射电子显微镜中热处理过程中，在样品上预定位置进行原位电子辐照。我们证明，通过控制入射电子束的位置，可以在纳米线上的所需区域形成多孔TiO ₂（B）晶体结构，这是传统合成方法难以实现的。当在原位加热时，晶体中的铅原子的原始纳米线的通过非弹性散射下入射电子迁移出来，而高的温度（> 400℃）为TiO 2的结晶提供能量₂（B）和相当数量的挥发铅原子，这使得生成的TiO ₂（B）纳米线是多孔的。相反，在400°C的温度下，偏析的Pb原子形成Pb颗粒，并且TiO _x纳米线保持非晶态。这项工作不仅提供从PX-PbTiO ₃到单斜TiO ₂（B）的相变的原位可视化，而且还提出了一种晶体学工程学策略，可在纳米级的受控位置获得所需的晶相。