Group leader

Kreiner, Guido
Guido Kreiner
Group leader
Phone: +49 351 4646-3324

Chemistry, Synthesis

Group members

Filsinger, Kai
Kai Filsinger
Graduate student

Synthesis

Stinshoff, Rolf
Rolf Stinshoff
Graduate student

Synthesis

Former Group Members

Fichtner, Tina
Tina Fichtner
Post-doctoral research scientist
Jamiyansuren, Bayardulam
Bayardulam Jamiyansuren
Graduate student

Synthesis, crystal structure and microstructural characterization

The main mission of the group is to prepare alloys of single- and multi-phased materials. Heusler and related compounds are the main focus. In addition, inorganic materials like pnictides and chalkogenides in form of high-purity compounds are prepared. Most of the alloys and compounds are functional materials. Examples are semiconductors, half-Heusler compounds, Li-based compounds as electrode materials, exchange bias materials, thermoelectric materials, hard magnetic materials, complex metallic alloy phases and magnetocaloric materials.

A large variety of alloying techniques and methods for specimen preparation are used. Inductive melting, arc melting, suction casting and tilt casting are used to prepare bulk samples, whereas ball milling and melt spinning is used for micro powders. Our laboratories are equipped with a large number of glove box systems, which allows to protect the alloys and compounds against oxygen and moisture. For heat treatment furnaces operating in different temperature regimes are used, e.g., fluidized bath furnaces for extreme temperature stability (± 0.1 °C) or high temperature furnaces up to 1700 °C.

<p style="text-align: justify;" align="center"><strong>Figure 1:</strong> (Left) Schematic view of a melt spinning apparatus with interior view of the vacuum chamber (melt spinner SC, Edmund Bühler GmbH). (Right) Metallic ribbon obtained by melt spinning.</p> Zoom Image

Figure 1: (Left) Schematic view of a melt spinning apparatus with interior view of the vacuum chamber (melt spinner SC, Edmund Bühler GmbH). (Right) Metallic ribbon obtained by melt spinning.

Each material is characterized regarding its chemical composition, crystal structure, disorder, defects, and microstructure. ICP-OES and –MS is used for the chemical analysis of most majority components and for impurities, respectively. Light weight elements like hydrogen, carbon, nitrogen and oxygen are determined by combustion analysis or hot gas extraction. Single crystal X-ray and powder X-ray diffraction (in-house and synchrotron) are used for crystal structure determination and phase analysis and neutron diffraction for determination of magnetic structures. Thermal analysis is used to determine phase reactions, to detect phase transitions and to study the melting behavior. The microstructures of the bulk samples are investigated by wet and dry etching, light optical imaging and scanning electron microscopy (SE and BSE images) and EDX mapping. Reliable information about the chemical composition of phases in multi-phased samples is obtained from electron probe microanalysis (WDX). EBSD is used for phase mapping and to study the distribution of the grain boundaries, i.e., the crystalline texture. The latter is of tremendous importance for controlling mechanical, magnetic and electrical properties.


In specific cases we study phase diagrams to obtain information on the phase stabilities and for planning crystal growth experiments. In addition, we explore alloying tendencies in a heuristic approach and use simple rules to predict phase formation and the crystal structures of novel compounds. In addition, first-principles calculations are used to guide alloy preparation. Selected examples are highlighted in the left menu.

 
loading content