Diffusion, thermotransport and thermodynamic properties of Ni-Zr melts: molecular dynamics study

Advanced theoretical work and establishing theoretical relations is the main focus of this work and was achieved via molecular dynamics simulation. By making use of statistical mechanics and atomistic modelling, an accurate and reliable database on Ni-Zr melts and its diffusion properties is generated, in conjunction with a semiempirical many-body interatomic potential for a better understanding of thermotransport and thermodynamic properties in the melts, which are used to identify possible glass-forming alloys. Comparison of simulation results with existing experimental data confirms the molecular dynamics approach used to be quantitative,and showcases the importance of theoretical work in this field. The developed theoretical approach within the framework of molecular dynamics, incorporates the Green-Kubo, as well as the Mori-Zwanzig formalisms, to derive expressions for diffusion properties of the melt in terms of time-correlation functions. Evaluation of self-diffusion coefficients and the kinetic part of the interdiffusion offer a detailed insight into the dynamics of Ni-Zr melts upon undercooling. A link between composition and temperature dependencies is established. Finally, the observed homogeneous dynamical slowdown of singleparticle and collective diffusion dynamics in the composition range of 0.25 ≲ 𝑐𝑐𝑁𝑁𝑁𝑁 ≲0.5 reveals enhanced stability of the melt against its crystallisation and therefore represents viable glass-formers. Further investigation of cross-correlation behaviour of the interdiffusion flux and the force caused by the difference in the average random accelerations of different atoms of an alloys different components in the hydrodynamic limit 𝑡𝑡 → 0 is presented. This is used to determine conditions in terms of a correction factor, 𝑆𝑆, and its decomposed parts, namely 𝑆𝑆0 and 𝑊𝑊12. The established theory is then applied on different types of melt with i) chemical ordering and ii) phase separation tendency. The main findings conclude, that for the first type of melt: 𝑆𝑆 < 𝑆𝑆0 (𝑊𝑊12 < 0); meanwhile for the second type of melt: 𝑆𝑆 > 𝑆𝑆0 (𝑊𝑊12 > 0) describing the atomic ordering behaviour.