Master's thesis defense meeting (Mr. Navid Ghayabi)

Title: Calculation of the pressure of amorphous crystal - ternary GST alloy and examination of the effects of nanovoids and dislocations on them using phase field method based on mechanics

Presenter: Navid Ghiabi

Supervisors: Mahdi Javanbakht

Reviewers: M. Salmani Tehrani,  S. Akbarzadeh 

abstract 

In recent years, extensive research has been conducted on phase-change materials, especially chalcogenide-based alloys, which have numerous thermal, electrical, and optical applications. One of these materials is the ternary GST alloy, consisting of germanium, antimony, and tellurium, which is particularly significant in phase-change memory due to its ability to change phase between crystalline and amorphous structures. Most previous studies have been based on thermodynamic methods, atomic simulations, and experimental approaches, but using the phase-field method as an innovative approach can assist in investigating the thermodynamics, kinetics, and structural changes of this material. This thesis examines the crystal-amorphous transition process in GST alloy nanolayers under the simultaneous mechanical and thermal loading using the phase-field model, and the transition pressure at different temperatures is extracted. The results of atomic simulations indicate that this pressure can increase to several gigapascals in defect-free GST alloy structures, whereas in commercial and laboratory samples, this pressure is significantly lower. One of the hypotheses to explain this reduction in pressure is the presence of structural defects, especially vacancies and dislocations (plasticity).