Ab initio study of the electronic structure and the EFG at Ta

R. E. ALONSO; M. TAYLOR; L. ERRICO; A. LÓPEZ GARCÍA

Ginebra

Congreso; 3rd Joint International Conference on Hyperfine Interactions and International Symposium on Nuclear Quadrupole Interactions.; 2010

Hafnia (HfO2) and zirconia (ZrO2) are wide band gap semiconductors with high dielectric constants and very similar properties. Both oxides have monoclinic structure at room temperature that transforms into tetragonal and cubic at respectively higher temperatures. Besides both oxides display technological interest because their high temperature melting point as well as its chemical stability. By adding small amounts of impurities present different structures that have important technological applications such as electrolytes for combustion cells, catalytic substrates and protecting coatings. Both, HfO2 and ZrO2 have been widely studied using Time Differential Perturbed Angular Correlations spectroscopy (TDPAC) using 181Hf→181Ta probes. Up to now the analysis of TDPAC results was based in the simple assumption that probes are inert in the sense that they do not introduce any crystalline or electronic distortion. The experimental studies observe two different pure quadrupolar interactions for the 181TA PAC probe. The most populated one was assigned to probes localized at the regular monoclinic Hf site while the other was not univocally understood. In this work, a detailed study of the different charge states for the impurity-probe atom (Ta) was performed in order to understand the second interaction observed in Ta-doped monoclinic HfO2 and ZrO2. The combination of experiments and theory suggests that two different charge states coexist in both compound. Moreover, one of this charge states is accompanied by a net magnetic moment that was never reported previously. Poster presentation