Determination of Polymorph Structures in Functional Metal Oxides Using Convergent Beam Electron Diffraction

Abstract

In binary metal oxides (BMO), polymorphic transitions can result in various crystallographic structures which have been shown to exhibit very different and distinct physical and chemical properties. Thus, exact structural determination is essential as these changes in their crystal structures offer fine control over a wide variety of different properties and, therefore, open up a wide field of applications. However, distinguishing between different BMO polymorphs is not trivial. A combination of high-resolution X-ray diffraction (XRD), Raman and infrared-ray (IR) spectroscopy might be perform to identify phases. However, this is not a universal approach because strategies for phase identification vary with materials system, and, in the case of BMO polymorphs, might not work at all because of limitations of standard Raman/IR spectrum data of inorganics crystal. Conventional electron-microscopy-based characterization techniques, such as selected area electron diffraction (SAED), nanobeam diffraction (NBE), highresolution TEM (HRTEM), high-resolution STEM (HRSTEM), provide information that is not always sufficient for polymorph determination, especially in nanocrystalline BMO. A general and universal approach to overcome this and to confirm a specific crystal structure is performing TEM tilt experiments obtaining data from at least 4-6 zone axis orientation (e.g., using SAED patterns, NBE patterns, HRTEM or HRSTEM images). However, this is a complicate experiment and, in case of beam-sensitive materials, this time-consuming approach might not work.

Emerging Fluorite-Structured Antiferroelectrics and Their Semiconductor Applications

“…Another factor contributing to the improved endurance of AFE-based devices is the stability of the fluorite-structured AFE film. The FE phase in a fluorite-structured material consists of the metastable o-phase, , and the fluorite-structured FE produced by ALD is polycrystalline. Thus, the obtained film contains a mixture of different thermodynamically stable phases, such as the t-phase, m-phase, and c-phase.…”