Iron pnictide superconductors

The scope of this dissertation therefore has not only been the synthesis of various new superconducting and non-superconducting iron pnictides of several structural families but also their in-depth crystallographic and physical characterisation. In Chapters 3 - 6, the family of the ZrCuSiAs-type (1111) compounds is subject of discussion. The solid solution series La(CoxFe1-x)PO is analysed regarding magnetic and superconducting properties and the new compounds EuMnPF and REZnPO, as well as the new superconductor parent compound SrFeAsF are presented. Chapters 7 - 9 are dedicated to the new iron arsenide superconductors of the ThCr2Si2-type (122 family). Therein, also the discovery of the first superconductor in this structural family, Ba0.6K0.4Fe2As2, is unveiled. A detailed examination of the complete solid solution series (Ba1-xKx)Fe2As2 is presented. Moreover, the crystallographic phase transitions of the closely related compounds SrFe2As2 and EuFe2As2 are characterised and the superconductors Sr1-xKxFe2As2 and Ca1-xNaxFe2As2 are examined for magnetic and phononic excitations. In Chapter 10, the redetermined crystal structure of the superconductor Fe(Se1-xTex) (11-type) is presented from a chemist's point of view. Chapters 11 - 14 look into the superconducting and non-superconducting iron arsenides of more complex structural families (32522-type and 21311-type). Therein, crystallographic and magnetic details of Sr3Sc2O5Fe2As2 are presented and Ba2ScO3FeAs and Sr2CrO3FeAs, the first two members of the new 21311-type are portrayed. Sr2CrO3FeAs is looked at in close detail with various methods, so e.g. the spin structure of the magnetically ordered compound is solved and a possible reason for the absence of superconductivity in this compound is given. Finally, the superconductor Sr2VO3FeAs is scrutinised and necessary prerequisites for superconductivity in this compound are suggested. (orig.)