Structural peculiarities of a moissanite (natural SiC) single crystal from Manchary kimberlite pipe, Yakutia

Abstract

Morphological features and internal structure of a large single crystal of moissanite - natural SiC - from a Manchary kimberlite pipe are characterized in detail using complementary methods including optical, atomic force and electron microscopy, cathodoluminescence, Raman spectroscopy and X-ray topography. The sample combines atomically flat (0001) faces decorated with growth macrosteps and with remarkably complex secondary (e.g., (10–13)) faces. These faces contain outcrops of dislocations, remnants of a crystalline film, features consistent with attachment of 3D growth nuclei and other peculiarities. The specimen mainly consists of 6H polytype with admixture of 4H and 15R polytypes. The overall crystalline quality is high, only few growth-related dislocations are visible in X-ray topographs. Morphological features suggest growth of the SiC crystal on a substrate in relatively stable, but nevertheless gradually changing conditions. These changes are reflected in complex internal zoning. As suggested by the growth features, at the last stages the supersaturation increased considerably, possibly resulting from closure of a growth chamber. The growth features are consistent with moissanite formation from a reduced supercritical fluid at moderate temperatures.