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The present work reported the intrinsic mechanical behavior of vanadium dioxide (VO2) thin film deposited on a SiO2 substrate using a combination of nanoindentation tests and a theoretical model. The effect of phase transition on mechanical parameters was studied by adjusting the test temperature. A new model that can simultaneously extract the elastic modulus and hardness was derived by introducing a dimensional analysis. The results showed that the thin film exhibits a hardness of 9.43 GPa and a Young's modulus of about 138.5 GPa at room temperature, compared with the values of 5.71 GPa and 126.9 GPa at a high temperature, respectively. It can be seen that the intrinsic mechanical parameters decrease to a certain extent after a phase transition. Finally, the numerical simulation results were consistent with those of the experiments, which verified the effectiveness of the new method. In addition, this study also provided useful guidance for mechanical tests on other ultra-thin films. [ABSTRACT FROM AUTHOR]

The engineering applications of thermoelectric (TE) devices require TE materials possessing high TE performance and robust mechanical properties. Research on thermal and electrical transport properties of TE materials has made significant progress during the last two decades, developing TE materials on the threshold of commercial applications. However, research on mechanical strength and toughness has lagged behind, restricting application of TE materials. Mechanical failure in these materials involves multi-scale processes spanning from atomistic scale to macro scale. We have proposed an integral stress-displacement method to estimate fracture toughness from intrinsic mechanical behavior. In this review, we summarize our recent progress on fracture toughness of TE materials. This is in three parts: (1) Predicting fracture toughness of TE materials from intrinsic mechanical behavior; (2) Intrinsic mechanical behavior and underlying failure mechanism of TE materials; and (3) Nanotwin and nanocomposite strategies for enhancing the mechanical strength and fracture toughness of TE materials. These findings provide essential comprehensive understanding of fracture behavior from micro to the macro scale, laying the foundation for developing reliable TE devices for engineering applications. [ABSTRACT FROM AUTHOR]