In-Situ High-Temperature Ferroelastic Phase Transformations in Oxide Ceramics

一个紧凑的，热成像炉已开发与同步辐射收集在现场高温粉末衍射数据在空气中选定的氧化物陶瓷高达2400 ℃。 实验数据进行了分析，并与理论预测的Rietveld晶体学，轮廓拟合技术。本研究项目的最终目的是研究所选材料的铁弹相变中涉及的晶体结构变化的详细机制，使用原位同步辐射XRD，热台光学显微镜和TEM技术。 具体地说，相变涉及可忽略不计或零体积变化，但可能一些晶胞形状的变化将集中在。 将研究钽氧化物（Ta 2 O 5）和镧系元素钽酸盐（LnTaO 4）以及镧系元素铝酸盐的相变。以这种方式，可以更好地理解材料的结构-性质关系并针对应用进行定制，例如，在增韧机制、大力驱动和形状记忆陶瓷方面。 本项目的目的是利用我们新发明的热成像炉，结合同步辐射，在空气中能够达到2400 ℃，对氧化物陶瓷的相变进行原位高温研究。 重点是氧化物材料表现出多晶型相变，特别是铁弹性质，在高温下。 这与我们正在进行的研究工作是一致的，我们正在寻找具有新的能量吸收机制的潜在材料，这些材料在设计坚韧的高温复合材料中有应用。 此外，由于铁弹机制的畴重排，可能在大的力驱动和形状记忆行为的潜在应用。

A compact, thermal-image furnace has been developed in conjunction with synchrotron radiation to collect in situ high-temperature powder diffraction data on selected oxide ceramics in air up to 2400 C. The experimental data is analysed and compared with theoretical predictions by the Rietveld crystallographic, profile fitting technique. The ultimate aim of this research project is to investigate detailed mechanisms of crystal structure changes involved in ferroelastic phase transformations in selected materials, using in situ synchrotron XRD, hot stage optical microscopy and TEM techniques. Specifically, phase transformations involving negligible or zero volume changes, but possibly some unit cell shape changes will be focused upon. Phase transformations in tantalum oxide (Ta2O5) and lanthanide tantalates (LnTaO4), as well as lanthanide aluminates will be studied. In this manner, the structure-property relationships of the materials could be better understood and tailored for application, e.g., in toughening mechanisms, large force actuation and shape memory ceramics. Preliminary studies will be made on some of the mechanical properties of key ferroelastic materials This objective of this project is to undertake in-situ high-temperature studies of phase transformations in oxide ceramics, using our newly-invented, thermal-image furnace, capable of 2400 C in air, in conjunction with synchrotron radiation. The emphasis is on oxide materials exhibiting polymorphic phase transformations, especially of a ferroelastic nature, at elevated temperatures. This is inline with our on-going research efforts in identifying potential materials with new, energy absorbing mechanisms, which have applications in the design of tough, high-temperature composites. Furthermore, as a result of domain rearrangement by ferroelastic mechanisms, potential applications are possible in large force actuation and shape memory behavior.