ABSTRACT

The crystal growth using Optical Floating Zone (OFZ) technique (employing halogen lamps and ellipsoidal mirrors for heating) is gaining importance since the first systems were introduced into the market in the ‘80. The growing number of OFZ apparatus used, proves the usefulness of this method in the growth of various complex oxides including high temperature superconductors, new magnetic materials and complex oxides with “exotic” oxidation states of some cations. Wide range of materials including metals, intermetallic compounds and semiconductors have been grown by this method. Crystals grown by the OFZ technique are of high quality but relatively small (usually not bigger than few mm in diameter and few cm long) so the majority of the work concentrates on exploratory growth of new materials - mainly for research purposes. There is limited industrial application of this method (Y₃Fe₅O₁₂ , TiO₂ and β-Ga₂O₃). The Laser Heated Pedestal Growth (LHPD) technique used for growth of oxide fibres for optical applications is an important variation of the FZ technique.
OFZ requires the starting material to be prepared in the form of high density, uniform ceramic rods (“feed rods”) and the quality of these rods is very important for the stability of the crystal growth process. Limited number of growth parameters (power, translations and rotations of crystal and feed rod) are accessible during the growth process and they can vary over a wide range depending on the material grown. The growth of incongruently melting oxides is possible using a variation of this technique called Travelling Solvent Floating Zone (TSFZ). This is interesting for exploration of new materials. In such a case a high temperature solution (flux) can be used or a “practical” steady state can be achieved in the self-flux approach. In all cases, some information about the phase diagram of materials to be grown is very important. OFZ method is also very well suited for producing crystals of solid solutions. The pressure and composition of growth atmosphere are both important to stabilize a phase with appropriate oxidation states of cations. Additionally, high pressure capabilities of some systems can help to grow volatile materials.
In this presentation the advantages and disadvantages of the FZ technique for growth of crystals of congruently and incongruently melting oxides and their solid solutions will be discussed. Additionally, important problems of crystal characterization and assessment of micro and macro defects will be presented.

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