Etch Pits in Flux-Grown Corundum

Procedures have been developed for chemically polishing and etching {0001}, {10 (1) over bar1), {10 (1) over bar2}, {11 (2) over bar0}, and {1 (1) over bar 00} planes in crystals of ruby and sapphire grown from a PbF(2) flux. The shape and the orientation of the etch pits were found to be characteristic for each plane and the density of the pits was 10(2) to 10(4)/cm(2). Similar pits were produced in flame-fusion material, but the density was 10(6) to 10(8)/cm(2), Ruby and sapphire crystals grown by the same process behaved similarly. There is evidence that etch pits reveal dislocations which emerge normally to the basal or to the prismatic planes, since similar patterns of pits were produced after the removal of successive layers of material parallel to these planes, and a correlation was found between the pit patterns on opposite {0001} faces. Inconclusive evidence on this point was obtained for the rhombohedral planes.