Y₂O₃:Eu and the Mössbauer isomer shift coefficient of Eu compounds fromab-initiosimulations

We report on a full potential density functional theory characterization of Y₂O₃upon Eu doping on the two inequivalent crystallographic sites 24dand 8b. We analyze local structural relaxation, electronic properties and the relative stability of the two sites. The simulations are used to extract the contact charge density at the Eu nucleus. Then we construct the experimental isomer shift (IS) versus contact charge density calibration curve, by considering an ample set of Eu compounds: EuF₃, EuO, EuF₂, EuS, EuSe, EuTe, EuPd₃and the Eu metal. The, expected, linear dependence has a slope ofα= 0.054 mm s^-1Å^-3, which corresponds to nuclear expansion parameter ΔR/R= 6.0 × 10^-5.αallows to obtain an unbiased and accurate estimation of the IS for any Eu compound. We test this approach on two mixed-valence compounds Eu₃S₄and Eu₂SiN₃, and use it to predict the Y₂O₃:Eu IS with the result +1.04 mm s^-1at the 24dsite and +1.00 mm s^-1at the 8bsite.