Thermoelectric properties of B-doped nanostructured bulk diamond with lowered thermal conductivity

Abstract

Diamond exhibits high wear resistance and high chemical resistance. If diamond exhibits high thermoelectric performance, the thermoelectric application will be expanded for various situations such as the use of friction heat on turbines. However, bulk diamond exhibits low electrical conductivity and high thermal conductivity, leading to the low thermoelectric performance. In this study, to solve the above problem, we propose a strategy of heavy impurity doping in nanostructured bulk diamond which brings two things: (1) higher thermoelectric power factor, and (2) phonon scattering enhancement at impurities and nanostructure interfaces reducing the thermal conductivity drastically. We investigate the thermoelectric properties of heavily B-doped nanostructured bulk diamonds prepared by direct conversion sintering under ultra-high pressure and temperature using B-doped graphite as a starting material. This nanostructured bulk diamond exhibited high electrical conductivity due to heavy B doping, resulting in high power factor of 4 μWcm−1 K−2 at 1050 K. Furthermore, we found that this nanostructured bulk diamond exhibited drastic thermal conductivity reduction, resulting in quite low thermal conductivity among bulk diamond ever reported. This comes from phonon scattering both at nanostructure interfaces and by substitutional B atoms. From these results, the present study would be informative for expanding thermoelectric application to various situations such as the use of friction heat.