Growth of Single Crystals of Cuprous Oxide in Silica Gels at Near Ambient Temperatures

Abstract

CRYSTAL growth in gels is becoming increasingly recognized as a promising technique for the preparation of single crystals of substances which are slightly soluble in water and which cannot be conveniently grown from the melt or from the vapour1. The growth of single crystals of many metal oxides is of considerable interest, particularly for basic studies of their electronic properties and other pertinent characteristics. Single crystal growth in gels at near ambient temperatures offers a possibility of obtaining specimens free from thermal strains and the impurities frequently associated with high temperature preparative methods. The preparation of single crystals of metal oxides in gels at low temperatures has not previously been successfully achieved, probably because of a strong tendency of metal oxides to form hydrated polycrystalline or amorphous precipitates in such media. We report the growth of single crystals of cuprous oxide in silica gels at near ambient temperatures by the controlled reduction of cupric sulphate with selected mild reducing agents such as hydroxylamine hydrochloride and hypophosphorous acid.