THERMAL-CONDUCTIVITY OF NATURAL AND SYNTHETIC DIAMONDS WITH DIFFERINGISOTOPE CONTENTS

The temperature-dependent thermal conductivity k(T) between 90 K and 5 50 K of CVD (chemical vapor deposition) diamond films, and the room-te mperature thermal diffusivity alpha(300) of synthetic diamond gems wit h different isotopic compositions, have been measured. In addition pre vious k(T) data for natural Type IIa diamond between 10 K and 1200 K w ere reanalyzed. Analysis of k(T), using a comprehensive Klemens-Callaw ay model, was directed towards understanding factors affecting the dra matic enhancement of room-temperature thermal conductivity k(300) of d iamond gems with increasing isotopic purity. We conclude that phonon-i sotope scattering in diamond gems alone is ineffective in explaining t he k(300) differences. Other factors such as isotope clustering or pho non-vacancy and other point defect scattering must also contribute to the reduction in thermal conductivity.