Floating Zone Growth of Oxides and Metallic Alloys

Single crystals of congruently and incongruently melting oxides have been grown by the optical floating zone (OFZ) and traveling solvent floating zone techniques. Both relatively low-cost methods work especially well for oxides melting above the maximum operating temperature of conventional crucibles or that were previously impossible to grow due to crucible oxidation or reaction of the melt with the crucible material. For incongruently melting oxides, solvents with experimentally determined composition allow for creation of practical steady state conditions. This extends the range of materials that now can be crystallized in oxidizing, reducing, and neutral atmospheres and elevated pressure. Distribution of dopants is relatively uniform.

The important problems of zone stabilization and its dependence on the conditions applied are discussed from the experimental point of view. Basic characterization of the grown crystals and most characteristic defects is presented. An extensive list of oxide crystals grown by the OFZ method is included.

Floating zone crystal growth with radio frequency (RF) heating is an important technique for the preparation of single bulk crystals. The absence of any crucible is advantageous for the growth of single crystals of reactive materials with high melting points. The melt convection driven by the induction heating and the heat radiation from the surface leads usually to a solid–liquid interface being concave toward the solid phase outer rim. These concave parts inhibit the growth of single crystals over the whole cross-section. The concave solid–liquid interface can be prevented by a two-phase inductor that melts the material but also stirs it in a certain way. The basic design of this two-phase inductor is given, and its application for the growth of industrially relevant single crystals of RuAl and TiAl intermetallic compounds as well as interesting compounds for research such as antiferromagnetic Heusler MnSi compounds or biocompatible TiNb alloys is described.