PROPERTIES OF DIAMOND WITH VARYING ISOTOPIC COMPOSITION

Gem-quality diamonds of varying isotopic composition have been synthesized by sequential application of chemical vapor deposition and high-pressure technologies of diamond growth. The resulting diamond crystals have a high crystal quality, a low defect density and low internal stresses. Their thermal conductivity increases with increasing isotope purity with the maximum thermal conductivities occurring with either isotopically pure 12C or 13C. The thermal conductivity is a symmetric function of isotopic composition with a minimum at 50% 13C. As the isotopic concentration is changed, the interatomic spacing decreases linearly with increasing 13C concentration. The intensity of the first-order Raman line also decreases with increasing 13C concentration. The wavenumber of the first-order Raman line is a monotonic but non-linear function of isotope concentration with the line wavenumber decreasing by 50 cm-1 from pure 12C to pure 13C. The two- and three-phonon absorption bands also move towards lower wave numbers with increasing 13C concentration. © 1992.