Tuesday, August 28, 2007, 1:30 pm — Small Seminar Room, Bldg. 510
Intermetallic compounds and oxides are of fundamental interest due to their exciting properties like superconductivity, magnetic ordering phenomena or the presence of quantum-critical points. Unknown phase diagrams, rather complex non-cubic crystal structures and - in case of transition metal oxides - the low dimensionality of the lattice and the instability of the oxidation state of the transition metal during melting are a big challenge for the growth of large single crystals with high chemical and physical perfection. Here we report crystal growth by traveling solvent floating zone methods of two classes of intermetallics – Rare Earth (R)-Ni-Borocarbides RNi2B2C with interplay of superconductivity and magnetic ordering and Rare Earth-Pd-Silicides R2PdSi3 (R = Y, Tb, Dy, Ho, Er, Gd, Tm) with complex magnetic ordering – and Transition Metal Oxides like CuO, MCu2O3 (M = Ca, Co, Sr, La) charge and spin spatial inhomogeneities and La4Sr10Cu24O41.
Stoichiometry control, high-purity constituents and reduction of oxygen traces in the ambient Ar atmosphere at any step of alloy preparation and crystal growth are prerequisites of high-quality samples of intermetallic compounds [1]. A stable molten zone, the convex interface shape governed by heating conditions, the choice of appropriate growth rates – typically 1 mm/s for RNi2B2C with incongruent melting behavior but 3 - 10 mm/s for congruent melting R2PdSi3 compounds – and intensive melt convection by counter-rotation of feed rod and seed are necessary.
Different from intermetallics, feed rods of oxide crystals grown by floating zone process with optical heating are received from a powder route which requires special care for powder mixing, appropriate temperature, pressure and time for sintering homogeneous rods with small porosity. The oxygen partial pressure during the growth process plays a crucial role for the growth oMCu2O3 and other transition metal oxides. Elevated oxygen pressure can change the phase diagrams i
Hosted by: Markus Hucker
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