Abstract
By heating amorphous boron near its melting point in a reactor grade graphite crucible it has been possible to produce single crystals of graphite containing up to 4% boron. These crystals have been studied before and after heat treatments by Electron Microscopy, X-ray Diffraction and Mass Spectrometer analysis. A model is proposed to explain the results which necessitates the boron occupying both interstitial and substitutional sites. The former causes a c-axis lattice parameter expansion, the latter caising a c-axis contraction and a-axis expansion. The interstitial population diffuses away after low temperature anneals of 1200°–1400°C whilst the substitutional boron 2% remains stable until 2000°C, when it diffuses away leaving behind a supersaturation of vacancies which precipitate as loops. Differences between vacancy loop distributions in specimens annealed before cleavage into thin foils and specimens cleaved after annealing lead to the conclusion that substitutional boron can diffuse along the c-axis in graphite.
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