Influence of optically active defects on thermal conductivity of polycrystalline diamond

We systematically studied the influence of optically active defects on thermal conductivity for polycrystalline diamonds (PCDs) with different colour, crystalline quality and impurity concentrations. The thermal conductivities of PCDs on the growth (top) and nucleation (bottom) surfaces were characterized with 3ω technique. It is found that the bottom surface shows lower thermal conductivity as compared to the top surface. This could be due to the higher defect density in the bottom surface. Defects analyzed includes non-diamond carbon phase, C-H stretching vibration, Si vacancy, and substitutional nitrogen (Ns⁰). Our results suggest that, for the top surface, the heat transport is mainly controlled by the concentration of Ns⁰. For the bottom surface, non-diamond carbon phase, Si vacancy, C-H stretch and Ns⁰ defects all lead to an obvious reduction in the thermal conductivity. Most importantly, we derived a well fitted equation that estimates the thermal conductivity by optical transmittance, and the equation was demonstrated to be valid at any wavelength in visible region.