High-Pressure Synthesis and Crystal Growth, Characterization and Thermodynamic Properties of Iron-Pnictide Superconductors and Related Systems

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The focus of this project rests on the synthesis of high-quality samples of Fe-pnictide and related superconductors, and the achievement of a detailed understanding of their structural, magnetic and superconducting properties. Special emphasis will be placed on high-pressure synthesis – a promising technique for obtaining high-Tc materials in this class of superconductors -, and highest-resolution thermodynamic studies, such as specific heat, thermal expansion and ultrasound propagation. The latter two techniques as well as resistivity measurements can be combined with hydrostatic (4He-gas) pressure. To reach these goals, we will proceed along to main lines, which are closely interconnected: i) Ambient- and high-pressure (AP/HP) synthesis as well as crystal growth; ii) Material characterization as well as thermodynamic and transport measurements at ambient and hydrostatic pressure on selected compounds. In i) the aim is to synthesize monophasic samples of LnFeAsO1-x Fy (Ln = La, Ce, Tb and Dy) at HP/high-temperature (HT) conditions; AP- and HP-crystal growth of AeFe2As2 (Ae = Ca, Ba) and their doped variants and samples of FeSe1-x both at AP- and HP-conditions. In ii), the structural and physical characterization will be performed by employing standard techniques, such as X-ray diffraction, resistivity and magnetic measurements. These results are indispensable input parameters for optimizing the synthesis conditions in i). Detailed studies of their thermodynamic properties will be carried out on selected high-quality materials. In particular, since the HP preparation will affect the structural, magnetic and superconducting properties differently, these studies aim at gaining a deeper insight into the mutual interplay of these properties.