Growth of Large Sodium Chloride Crystals from Solution for Color-Center Studies

Sodium chloride single crystals with edge dimensions as large as 2.5 cm were grown from aqueous solutions. Solutions were purified by chemical precipitation of trace contaminants and filtration through membrane filters. Crystal defects were apparent in the initial stages of growth, but the outer portions of crystals were free of dislocations. F-band coloration by x rays at room temperature was not linear and the ``first stage'' was either absent or nearly so. Transition from extrinsic to intrinsic dc conductivity occurred at 350°C with the extrinsic conductivity two orders of magnitude lower than for ``pure'' melt-grown crystals.