High pressure and microwave based synthesis of transition metal pnictides

The goal of this thesis was to explore the possibilities of synthetic methods that are not very common in current transition metal pnictide research. The substitution of the Ca-site in CaFe₂As₂ with rare earth elements such as Pr the has been reported to induce superconductivity. However, some inconsistencies in the data suggested a non-intrinsic origin of the observed diamagnetic signal. Furthermore a solubility limit of 13% was found when prepared in an electrical furnace thus leaving a huge part of the physical phase diagram inaccessible. A high pressure/high temperature synthesis was developed to allow access to the whole doping range and an in-depth characterization of this compound was carried out. During the experiments concerning the high pressure synthesis of Ca_1-xPr_xFe₂As₂ the new ternary iron arsenide CaFe₅As₃ was identified and classified as a member of the Ca_n(n+1)/2(Fe_1-xM_x)_(2+3n)M'_n(n-1)/2As_(n+1)(n+2)/2 (n = 1-3; M =Nb, Pd, Pt; M' = □, Pd, Pt) family. The complete solid solution Ca_1-xPr_xFe₅As₃ (O ≤ x ≤ 1) was prepared and physically characterized. Furthermore, several useful techniques were developed to aid in future high pressure based investigations of transition metal pnictides. The second part of this thesis concerns a completely different, but equally promising synthetic approach. Microwave based synthesis is a well-established technique in many solution based fields, such as organic, medicinal or nano chemistry. For solid state and materials research several parameters and particularities have to be considered. But when successful, it allows for the reduction of reaction time by several orders of magnitude. It has very rarely been applied in the preparation of pnictides and on1y once in the context of pnictide superconductor research. The possibilities of this method were explored and employed in the preparation of several binary starting materials some of which are superconductors themselves. To really take advantage of the quickness this method offers, a dopant screening strategy was developed and applied to Ca₂Cu₆P₅, a very poorly investigated system that shares many features with 122-type pnictide superconductors. Arsenic was identified as a suitable dopant, the solid solution Ca₂Cu₆P_5-xAs_x (0 ≤ x < 2) was prepared and its structural behavior as well as its physical properties were characterized.