THERMAL-CONDUCTIVITY OF NATURAL AND SYNTHETIC DIAMONDS WITH DIFFERING ISOTOPE CONTENTS

The temperature-dependent thermal conductivity k(T) between 90 K and 550 K of CVD (chemical vapor deposition) diamond films, and the room-temperature thermal diffusivity alpha(300) of synthetic diamond gems with different isotopic compositions, have been measured. In addition previous k(T) data for natural Type IIa diamond between 10 K and 1200 K were reanalyzed. Analysis of k(T), using a comprehensive Klemens-Callaway model, was directed towards understanding factors affecting the dramatic enhancement of room-temperature thermal conductivity k(300) of diamond gems with increasing isotopic purity. We conclude that phonon-isotope scattering in diamond gems alone is ineffective in explaining the k(300) differences. Other factors such as isotope clustering or phonon-vacancy and other point defect scattering must also contribute to the reduction in thermal conductivity.