Rafal Abdank-Kozubski
Jagiellonian University in Krakow, Poland
Title: Saddle point energies for atomic jumps and thermodynamic activation energy for ordering and diffusion in intermetallic compounds: Atomistic simulations
Biography
Biography: Rafal Abdank-Kozubski
Abstract
Chemical ordering and diffusion are controlled by atomic migration, which in the case of solid intermetallic compounds, proceeds predominantly via elementary atomic jumps to vacancies. The macroscopic rates of both phenomena parameterized by diffusivities (diffusion) and relaxation times (chemical ordering) show temperature dependences quantified by thermodynamic activation energies usually evaluated through the Arrhenius analysis. The atomistic origin of the phenomenon consists of the thermal activation of the atomic jumps described in terms of the “activated-state-rate” theory involving the probability of the atomic displacement from the original lattice site to the intermediate lattice position corresponding to the energetic saddle point. The saddle-point energies are modeled for diverse intermetallic compounds using various concepts and techniques implemented with diverse Hamiltonians. The results are then used as parameters of Kinetic Monte Carlo simulations of ordering and diffusion, whose Arrhenius analysis yields thermodynamic activation energies. Correlation between thermodynamic activation energies for chemical ordering and diffusion and the values and relationships between the saddle-point energies is widely discussed. In particular, the origin of the relationship between the thermodynamic activation energies for ordering and Ni tracer diffusion in NiAl is elucidated in the above terms.