Growth of Single Crystals of Incongruently Melting Yttrium Iron Garnet by Flame Fusion Process

Abstract

Single crystals of yttrium iron garnet (Y3Fe5O12) have been grown using the flame fusion process, even though the compound is reported to melt incongruently. The growth of these single crystals involves a mechanism different from that which has been proposed for the growth of single crystals of incongruently melting mullite. Crystal boules were grown at varying linear growth rates and analyzed with chemical, X‐ray, and metallographic techniques. With high linear growth rates, the samples are uniformly polycrystalline and three‐phase, containing Fe2O3, YFeO3, and Y3Fe5O12. When slow linear growth rates are used, single‐crystal Y3Fe5O12 can be grown. The mechanism is as follows: At the beginning of growth the first phase to precipitate is YFeO3, and during this stage in growth the molten cap becomes enriched in Fe2O3, compared with the Y3Fe5O12 composition. The liquid cap composition thus changes to the limit of the peritectic on the Fe2O3‐rich side, and Y3Fe6O12 then crystallizes from the bottom of the melt as Y3Fe5O12 powder is added to the top of the molten cap. The central sections of these boules are single‐crystal yttrium iron garnet.