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Temperature dependence of the EFG at Cd‐doped Lu 2 O 3 : How ab initio calculations can complement PAC experiments

“…There is an important point to be taken into account: the charge state of the impurity-host system, the single acceptor Cd 2+ in Lu 2 3+ O 3 2-. When a Cd-atom replaces a Lu-atom, the resulting system is metallic because of the lack of one electron necessary to fill the oxygen p-band.…”

“…In 1999 we report the first PAC results of the EFG characterisation at 111 Cd impurities located at both non-equivalent cation sites of Lu 2 O 3 [3]. In Fig.…”

“…Lutetium is the only rare-earth that presents a closed-shell electronic structure in its 3+ oxidation state, converting this oxide into an interesting "laboratory" to check the models proposed to explain the phenomena mentioned above. In 1999, we presented results of PAC experiments in Lu 2 O 3 ( 111 Cd) and we explained the observed "step-like" temperature dependence of the EFG at 111 Cd sites in the framework of a two state model [3]. For a long time, the EFG in solids was estimated performing calculations based in the point-charge model in combination with Sternheimer factors.…”

“…Meanwhile HFID is essentially constant with temperature, HFIC presents an "step-like" temperature dependence. This EFG temperature dependence was explained in terms of a two state model that considers extremely fast fluctuation between two static EFG configurations [3]: in Lu 2 O 3 , the Cd impurities should introduces an acceptor level in the band gap of the semiconductor. The electronic population of this level (ionisation) change the local electron density at the PAC probe, thus changing the EFG.…”

Diagnostics of linear and incremental approximations in 4D‐Var

“…There have been several studies discussing the validity of the linear assumption in weather forecasting, such as those by Errico et al (1993), Vukićević and Errico (1993), Errico and Raeder (1999), Janisková et al (1999), Mahfouf (1999) or Gilmour et al (2001). As summarized by Pires et al (1996), the general conclusion is that, for large-scale flows, the linear approximation is valid for periods of two to three days and, for mesoscale flows, for periods of the order of 36 hours.…”