Stefan Berendts

High temperature optical spectroscopy investigations on Zr0.78Y0.18Sm0.04O1.89 and Zr0.78Y0.18Ho0.04O1.89 single crystals

Results are reported from a temperature dependent optical study of the title compounds performed at temperatures up to 1323 K. Absorption maxima and integrated absorption of rare earth f-f transitions exhibit a considerable temperature dependence, which is quantitatively described in the framework of the optical high temperature spectroscopy of d-ions. A strong, reversible band gap shift of doped and pure YSZ is observed and evaluated according to the Tauc equation. Single crystals of the title compounds were prepared by the skull melting method. Their linear expansion coefficients were determined by high-temperature X-ray diffraction.

Thermogravimetric and X-ray diffraction investigation on carbonated lanthanum oxide and lanthanum hydroxide formed in humid CO 2 atmosphere

Lanthanum oxide compounds are of great interest because of their wide range of applications (e.g., heterogeneous catalysis). It is well known that lanthanum oxide compounds, like lanthanum oxide, have to be handled carefully in a humid atmosphere due to their hydration affinity. Furthermore, lanthanum hydroxide has a high CO2 affinity and partially forms basic carbonates. The amount of carbonate impurities that are formed in air remains nearly constant over a long time. To investigate the carbonation process in more detail, lanthanum hydroxide and lanthanum oxide were stored in a controlled humid CO2 atmosphere. The results of thermal analysis (TA) and X-ray diffraction (XRD) prove a transformation of lanthanum hydroxide as well as lanthanum oxide to lanthanum carbonate via lanthanum hydroxide carbonate.