Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

Zirconia (ZrO2) doped with lanthanides, such as cerium (Ce), has been extensively studied for a multitude of tailored applications. The ZrxCe1-xO2 solid solutions can occur in three stable structures: monoclinic (m), tetragonal (t), and cubic (c), but also in several metastable ones (t′, t′′, κ, and t*)1. The phase transformation depends on the dopant concentration and the synthesis conditions, such as sintering temperature or cooling rate. In this study, to understand the behavior of cerium in the zirconia structure, 5 solid solution compositions with Ce4⁺ concentrations of 14, 18, 22, 26, and 30 mol % were synthesized through co-precipitation route. As an additional structural probe, a figurative amount of europium was added to the samples to enable luminescence spectroscopic analyses (TRLFS). In addition to these TRLFS investigations, the phase compositions were evaluated by Raman spectroscopy and synchrotron powder X-ray diffraction (PXRD). The PXRD results show that the diffraction peak around 14.9o can be attributed to the tetragonal phase, and the amount of this phase increases with increasing Ce concentration. Due to the substitution of Zr4+ by the larger Ce4+cation, the diffraction peaks are shifted to lower 2, here from 14.92 to 14.87o2. The t’ and c phases are not easy to distinguish. Owing to the high-resolution PXRD data, however, the diffraction peak around 16.91o could be attributed to the t’ phase and the peak at 16.77o to the cubic one. Both peaks could be identified in the compounds with more than 22 mol % of Ce3. At this concentration, no more monoclinic phase could be detected. TRLFS measurements of the Eu environment, corroborated the presence of the above mentioned phases, going from the dominant monoclinic to tetragonal metastable and cubic phases with increasing Ce substitution4. Combining the PXRD, TRLFS, and Raman data, no solid phase separation (CeO2+ZrO2) was detected.