FIGURE D.1 Molten zone under stable growth conditions in a floating-zone furnace. From top to bottom: polycrystalline feed rod, molten zone, growing crystal. The image of the filament is clearly seen. SOURCE: Courtesy of Robert J. Cava, Princeton University.

atmosphere is straightforward. While flux methods are more efficient for exploring a complex compositional phase space, FZ crystal growth is the best and most generally applicable growth method when large, high-purity crystals of known materials are required. In many cases, crystals of cubic centimeter volumes can be routinely grown.

While such crystals impact the full spectrum of physical measurements, the greatest beneficiary of the FZ technique has been the neutron-scattering community. The relatively low flux of current-generation neutron sources demands large single-crystal samples, and the FZ approach has been able to deliver materials that meet this demand. Indeed, the increasing availability of large, high-quality specimens has led to breakthrough advances in fundamental neutron-scattering measurements in high-temperature superconductivity, colossal magnetoresistance and related magnetic oxide physics, ferroelectricity, multiferroics, geometric frustration, and many other areas. The success of future facilities, such as the Spallation Neutron Source, will be intimately tied to the broad availability of FZ-grown crystals. It is no wonder that Princeton University’s Robert Cava has declared the FZ technique “arguably the best thing to happen to single-crystal growth in the past 25 years” and called for a 10-fold increase in the number of floating-zone crystal growth furnaces in the United States.

While the success of the optical-image FZ technique for the growth of oxide crystals speaks for itself, there are opportunities for improving this already powerful technique to further enhance its impact. These opportunities call for research and development on FZ furnace design and operation. The areas for continuing development are as follows: