Influence des caractéristiques d'un agrégat polycristallin sur la croissanceàl'état solide d'un monocristal de ferrite hexagonal

Abstract

We give a method of single crystal growth for BaFe 12O 19 entirely in the solid state, in a cylindrical polycrystalline aggregate of very small grains. This method is based on the control of discontinuous or exaggerated grain growth. We use neither crucible nor flux. Single crystal growth occurs at relatively low temperatures, therefore the thermal defect concentration is reduced. A single crystal growth rate of 25 mm/h normal to the c axis was attained. Single crystals ≅ 10 mm in diameter and several centimeters in length have been obtained. We draw attention to the effect of the main parameters of the polycrystalline aggregate, i.e. crystal diameter and its standard deviation. It is shown that decrease of the standard deviation makes solid state crystal growth possible without any thermal gradient. We point out that the effect of the thermal gradient on the crystal growth rate may originate from the migration of residual voids.