The optical floating zone technique: A review of experimental procedures with special reference to oxides

Crystal growth using the optical floating zone technique has been extensively used to grow a variety of bulk crystals, particularly single crystals of metal oxides. A comprehensive review of the literature has identified the most important experimental variables during image furnace crystal growth to be the nature of the feed rod, the growth rate, the growth atmosphere and gas pressure, the temperature gradient within the sample, the molten zone temperature and the rotation rate. The evidence from the literature further suggests that in order to prepare high quality crystals, these experimental variables typically need to be closely tailored to the characteristics of the material being grown. However, little attention appears to have been given to investigating in detail the effects that varying these experimental parameters can have upon crystal growths; for example, few reports seek to explain in a scientific way why a specific combination of parameters has been chosen for a particular growth. This article attempts firstly to collate the available evidence describing experimental procedures used during image furnace crystal growth and then to relate it to both the actual zoning process and the eventual crystal quality. Since the vast majority of the reported work using image furnaces has involved oxides, this article inevitably reflects this bias, although other types of materials are also covered.