Prof.  Mahdi  Javanbakht
Isfahan University of Technology,  Iran

Title: Coupled mechano-electro-thermal model to predict phase transition in phase change materials

Abstract:

The phase transition (PT) in phase change materials (PCMs) can be triggered by external stimuli, e.g., mechanical loading, light, voltage or heat, resulting in a drastic change in their physical properties, such as electrical resistivity. Due to this rapid PT, PCMs are promising candidates for various applications, including reconfigurable electronics, photonics, sensors, and memory devices. Here, a coupled phase field model is developed to investigate the effect of mechanical stress on the PT of Germanium-antimony-tellurium (GST). The results suggest that mean compressive stress promotes crystal growth, while tensile stress hinders crystallization. Moreover, stress alters the morphology and promotes anisotropic growth. The model is also advanced based on Murnaghan's equation of state to investigate high-pressure amorphization of crystalline GST for the first time, which can replicate the temperature dependency of the amorphization pressure. As results, the difference between onset and completion amorphization pressure for defective c-GST and the importance of void/vacancy clusters in lowering the amorphization pressure are successfully captured, in agreement with experimental/atomistic results. The model is also advanced to capture the crystallization/amorphization of GST nanofilm under external voltage which depicts the intricate interplay between temperature, stress, pre-existing defects, and PT in GST and allows to calculate the critical crystallization voltage vs. its pulse time. The proposed model allows for a better quantification of crystallization/ amorphization of PCMs under mechanical loading, heat and voltage.

Biography:

Ph. D, Mechanical Engineering, Iowa State University, 2013
Thesis: Phase-field approach to surface-induced phase transformations and dislocations.
Post Doctoral Research Associate, Aerospace Engineering Department, Iowa State University, 2013-2014.

Areas of Interest
-Phase Transformations, Large Deformation of Solids, Continuum Thermodynamics and Kinetics, Micromechanics and Nanomechanics, Phase Field Approach, Dislocation Theory, Smart Materials and Structures, Composite Materials, Computational Mechanics/FEM/COMSOL