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Growing uranium and cerium pnictide crystals by chemical vapor transport and flux methods

Zygmunt Henkie 

Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P.Nr 1410, Wrocław 50-950, Poland

Abstract

 Our knowledge of various compounds increases more effectively when they are studied within series of their homologs. Sometimes however, chemical properties of compounds in series strongly vary and growing their crystals requires serious modification of used methods. We illustrate this problem with an example of crystal growth of binary uranium pnictides of UX, U3X4 and UX2 stoichiometries (X = P, As, Sb, and Bi). Uranium phosphides and arsenides of U3X4 and UX2 composition could be grown by chemical vapor transport (CVT) in quartz ampoules at temperatures in range 750 - 950 oC, with iodine as a transporting agent and temperature gradient ~ 100 oC. Grown crystals were of excellent quality allowing quantum oscillations studies. UP, UAs, USb, and U3Sb4 could be grown by the CVT on tungsten rings heated up to temperature 1200 ÷ 1400 oC by induction furnace. The rings were suspended in a quartz bulb with substrates at its bottom - the coldest place in the bulb (600 ÷ 700 oC). Keeping a respectively low temperature of the quartz its reaction with uranium was greatly reduced. USb2 and UBi2 were grown by the self-flux method, where the driving force of the crystal growth was gradual decrease of temperature at rate ranging from 0.5 oC/hr at 1000 oC to 4 oC/hr at room temperature. Crystals of U3Bi4 were grown at constant temperature of 1080 oC in a U-Bi solution attaining over-saturation by slow evaporation of Bi due to the special construction of a graphite crucible heated with induction furnace. Various RET4As12 (T = Fe, Ru and Os; RE = La, Ce, Pr, and Nd) skutterudite crystals first-ever obtained, were grown in Cd:As or As fluxes in a self made pressure cell. Owing to high sensitivity of CeFe4As12 hybridisation gap semiconducting state on stoichiometry defects we observed a clear dependence of the grown CeFe4As12 crystals morphology on very low amount of stoichiometry defects.

 

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Presentation: Invited oral at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 1, by Zygmunt Henkie
See On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17

Submitted: 2013-04-15 12:43
Revised:   2013-07-17 22:51