Modulation of the Electron-Phonon Coupling in 3C-SiC by Lattice Defects and its Ramifications on the Thermal Spike

Silicon carbide is a high-temperature ceramic with numerous commercial and industrial uses. In the nuclear power industry, SiC is a coating in tri-isostructural (TRISO) fuel particles. It will soon be employed as a component in Accident Tolerant Fuel cladding and as a structural material in the flow channels of fusion systems. Consequently, radiation effects in SiC has been an area of intense study going back several decades. One subtle and little-studied aspect of primary radiation damage is the energy coupling between the excited electronic structure and the atomic lattice. Here we present a first principles study of the electron-phonon coupling (EPC) in 3C-SiC and discuss its effects on the dynamics of the thermal spike. Density Functional Perturbation Theory (DFPT) calculations were performed for both pristine and defective SiC. The EPC was found to be highly sensitive to the electronic temperature and the presence of lattice imperfections. In contrast to the behavior of the EPC in metals, the EPC in SiC can vary by several orders of magnitude and cannot, in general, be regarded as a constant.<br/><br/>The ramifications of the variable coupling on the spatial and temporal evolution of the thermal spike produced by swift ions or neutron-induced displacement cascades were studied within the framework of the Two-Temperature Model. In cases of low ion/PKA energy, use of a constant, effective coupling can be partially justified. However, for higher energy particles such as swift heavy ions, there are large spatial and temporal variations in the coupling strength, to the point where some of the assumptions of the Two-Temperature Model break down.