Author Description

In this thesis electronic structure calculations are applied to gain fundamental insight into physical mechanisms giving rise to specific material properties. The metal-insulator transitions of the vanadium Magneli phases VnO2n-1 are studied by identifying the relevant electronic states and analyzing their response to structural modifications. This investigation is based on a systematic understanding of the various crystal structures, including those of VO2 and V2O3. It is possible to study the relations between structural and electronic properties at the metal-insulator transitions of the latter oxides on a common basis. Similar crystal structures allow for the knowledge of the phase transitions in the vanadium oxides to be transferred to the titanium Magneli phases. Octahedral tiltings, as found in the ruthenates ACu3Ru4O12, are the most important class of structural distortions affecting perovskites. Analyzing the relationship between tiltings and electronic features paves the way for a universal picture of octahedral tilting. Furthermore, a family of quasi one-dimensional materials characterized by extraordinary magnetic properties is addressed. Motivated by band structure calculations for Ca3Co2O6 the related compounds Ca3CoRhO6 and Ca3FeRhO6 are investigated, allowing for insight into the details of the magnetic coupling. In der vorliegenden Dissertation werden Bandstrukturrechnungen eingesetzt, um Einblicke in physikalische Mechanismen zu erlangen, welche charakteristische Materialeigenschaften zur Folge haben. Zur Untersuchung der Metall-Isolator-Ubergange der Vanadium Magneli Phasen VnO2n-1 werden zuerst die relevanten elektronischen Zustande identifiziert und anschlieaend deren Reaktionen auf strukturelle Modifikationen analysiert. Dieses Vorgehen basiert auf einem systematischen Verstandnis der einzelnen Kristallstrukturen, einschliealich derjenigen von VO2 sowie V2O3. Es ist moglich die Beziehungen zwischen den strukturellen und elektronischen Eigenschaf