Revaling the mechanism of microscopic kinking phenomena in Hf6Ta2O17 superstructures

Abstract

As a promising candidate for a new-generation thermal barrier coating material, Hf6Ta2O17 is characterized by its unique long-period superstructures and excellent mechanical properties. In this study, the unique "kinking" phenomenon of the atomic arrangement in Hf6Ta2O17 crystals is directly visualized via high-resolution transmission electron microscopy for the first time. The evolution of the microstructure, and particularly the micro-mechanism of the "kinking" phenomenon, have been further explored by first-principles calculations. The study suggests that this phenomenon is primarily triggered by the rotation of the polyhedral structure, resulting from the partial elongation or shortening of the Ta-O bond length. These structural alterations are believed to directly influence the macroscopic mechanical properties and can improve the tensile properties of the Hf6Ta2O17 crystals. The findings of this study provide an important microscopic perspective for understanding the strain-induced crystal structure transformation. The quantitative analysis of the strengths of Ta-O and Hf-O bonds in different coordination polyhedra reveals the electronic structure changes behind the crystal structure transition, thus providing a new theoretical basis for an in-depth understanding of the behavior of crystals under the external stress.