Concentric dislocation loops with [0001] burgers vectors in ice single crystals doped with NH3

Ice single crystals, both pure and doped with NH 3 , were grown from the melt by a modified Bridgman method. The low dislocation density obtained (approximately 10 2 cm 2 ) made it possible to take x-ray diffraction topographs showing many concentric dislocation loops in the NH 3 -doped ice as well as occasional loops in the pure ice. The origin of these loops is attributed to the bunching effect of the steps produced by non-uniform distribution of impurities.