Structure and properties of the rare earth transition metal silicides

Rare earth disilicides RSi${}_2$ and their related R${}_2$TSi${}_3$ compounds crystallize in hexagonal AlB${}_2$- as well as in tetragonal ThSi${}_2$-like crystal structures, which possess a large structural variety, especially concerning the ordering of the T and Si atoms. Based on an extensive literature research with more than 300 articles and 500 structural reports this crystallographic family was characterized in detail and the symmetry relations were elaborated. The resulting Bärnighausen diagram comprises six additional structure types compared to previous publications. Partially, the corresponding space groups were determined here for the first time. Furthermore, relations between the incorporated elements within a compound and its properties were acquired. For instance, ordered structures form more frequently if a thermal treatment was applied. In addition, a correlation between the electronic structure of Hückel arenes and the Si/T ordering was discovered. This work is complemented by density functional theory calculations, which on the one hand provide information about formation energies and thus about the potential stability of previously unreported compounds. On the other hand, Bader charges of the atoms were calculated, which for example reduced possible superstructure models in the tetragonal lattice to only one plausible model. This work is completed with own results from resonant synchrotron experiments, exemplarily conducted on the representative with the largest super structure: Ho${}_2$PdSi${}_3$. For this compound additional structure models existed, but these can be excluded thanks to the results of the present work.