Preparation, characterization and physical properties of new compounds in the system Ln2O3 - ReO2 – ½ Re2O7 (Ln=lanthanides or yttrium)

The aim of this thesis has been the preparation of new phases in the system rare-earth – rhenium – oxygen (Ln2O3 - ReO2 – ½ Re2O7, with Ln = Lanthanides and Yttrium), the solution of their crystal structures with X-ray or neutron diffraction and their physical properties as conductivity or magnetic behaviour. Detailed descriptions are given for the preparation methods of new compounds with the compositions (Ln0.81Re0.19)3O5.64, Ln6ReO12, Ln5Re2O12, Ln3ReO8, Y7ReO14-d , Y3-xRe1+xO8 and Re3O10 and their structure solutions using powder or single crystal data. Measurements of the magnetization yielded deviations from the ideal paramagnetic behaviour at low temperatures for all compounds Ln6ReO12 (Ln = Ho, Er, Tm), Ln5Re2O12 (Ln = Er), Ln3ReO8 (Ln = Gd – Lu) and Y7ReO14-d . Only Yb5Re2O12 shows a significant deviation already at 100 K, Lu6ReO12 shows paramagnetic behaviour down to 1.7 K. Resistivity measurements has been carried out for the compounds Ln3ReO8 (Ln = Eu, Dy,Y). All samples appeared as semi conductors with band gaps of 192.2 meV for Eu3ReO8, 159.7 meV for Dy3ReO8 and 157.4 meV for Y3ReO8