AbstractsChemistry

Research Doctorate - Doctor of Philosophy (PhD) In this study, the phonon dynamics and lattice thermal conductivity of f.c.c. Copper (Cu), Aluminium (Al), Nickel (Ni) and Silver (Ag), as case studies, are investigated over a wide range of temperatures in detail. Calculations are performed within the framework of equilibrium molecular dynamics simulations in conjunction with the Green-Kubo formalism. To describe the interatomic interaction, the most reliable embedded-atom method potentials are used. It should be noted that for Ni two different embedded-atom method interatomic potentials are considered. Hereafter, the first potential is referred to as NiEAM1 (published in 1999) while the second potential is referred to as NiEAM2 (published in 2004). In all the models considered, a two-stage decay in the heat current autocorrelation function was observed. After the first stage of decay, the heat current autocorrelation function showed a peak in the low temperature range. The intensity of the peak decreased as the temperature increased. Furthermore, it transformed to a shoulder which diminished at high temperatures. It was revealed that the lattice thermal conductivity of a monatomic lattice can be decomposed into two contributions due to the acoustic short- and long-range phonon modes. These two contributions can be presented in the form of simple kinetic formulas consisting of the products of the heat capacity, the square of the average phonon velocity and the average relaxation time of the acoustic short- and long-range phonon modes, respectively. In addition, this analysis allowed for numerical evaluations of all these quantities, in a self consistent manner, from the heat current autocorrelation function. In particular, it was shown that the average phonon velocities of the acoustic short- and long-range phonon modes must be equal to each other and can be expressed via second-order fluctuations of the heat current vector. This was followed by an extensive consideration of the spectral representation of the analytical model for the heat current autocorrelation function. This has the potential to be used to efficiently decode the generic information on the lattice thermal conductivity and phonon dynamics from spectroscopic measurements, with no gradients imposed on the studied crystal, if a proper resolution of the frequency range of approximately 1 – 20 THz is accessible. In this research, the contribution to the lattice thermal conductivity determined by the phonon-electron scattering processes was intentionally ignored, and only the contribution due to the phonon-phonon scattering processes was considered. However, during comparisons of the data with the experiments, an estimation of the first contribution was made. Moreover, it is also of great interest, for practical applications, to have simple scaling relations between the lattice thermal conductivity and the other lattice properties readily accessible in experiments, such as the thermal expansion and elasticity. In this context, the scaling relations of the… Advisors/Committee Members: University of Newcastle. Faculty of Engineering & Built Environment, School of Engineering.