GROWTH OF CDS IN SEALED SILICA CAPSULES

Using emission and mass spectrographic techniques it has been demonstrated that carbon monoxide is evolved from a silica capsule when it is sealed-off from a vacuum system. Consequently crystals of CdS grown by sublimation down a temperature gradient in sealed, evacuated silica capsules were in fact grown in the presence of carbon monoxide at a pressure of the order of 1 Torr. At elevated temperatures the CO reacts with the CdS to form CS2 and COS. The variability in the quantity of CO evolved during seal-off accounts for the observed variations in the quantity of material transported in different growth runs. Experiments are also reported which demonstrate that silica tubing is porous to certain metallic ions when it is held at a temperature near 1150°C. Because of this effect many crystals grown in this laboratory have, in the past, been accidentally contaminated with copper. © 1979.