Single crystal growth of actinide compounds

Abstract

During recent years, the importance of solid state actinide research has been increasingly recognized. Further progress in actinide solid state physics depends on the availability of pure and perfect single crystals. Actinide compounds have large magnetic anisotropy with anisotropy fields of 8 × 10 7 A·m −1 or higher. Investigation of the mechanism responsible for such unique behaviour requires large single crystals of high purity for magnetization, neutron diffraction, angular and energy dependent photoemission measurements. Materials of interest for actinide solid state research are the metals and compounds with simple crystal structures like dioxides (CaF 2 structure), monopnictides and monochalcogenides (NaCl structure), and intermetallic compounds (Laves phases). This article gives an overview of actinide single crystal growth facilities in Karlsruhe and Geel. The actinide compounds are prepared by direct synthesis from the purest elements available using non-contaminating techniques. The reaction occurs in vacuum sealed quartz tubes where the actinide metal reacts with the vapour of the other element, or by levitation melting in a Hukin crucible. Different techniques have been developed to grow single crystals of actinide metals and compounds. High temperature solution growth from molten salts is used to prepare actinide dioxide single crystals. Oxides, pnictides and chalcogenides are grown by chemical vapour transport. Large single crystals of the monopnictides and monochalcogenides are obtained with the recrystallization (or mineralization) technique in sealed tungsten crucibles. Single crystals of congruently melting intermetallic compounds are pulled from levitated or semilevitated melts by the Czochralski method. Selected single crystals are characterized, orientated and encapsulated for safe handling during measurements.