Y₂O₃:Eu and the Mössbauer isomer shift coefficient of Eu compounds from ab-initio simulations

Abstract

We report on a full potential density functional theory characterization of Y2O3 upon Eu doping on the two inequivalent crystallographic sites 24d and 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, EuPd3 and the Eu metal. The, expected, linear dependence has a slope of α = 0.054 mm s−1 Å− 3, which corresponds to nuclear expansion parameter ΔR/R = 6.0 × 10−5. α allows to obtain an unbiased and accurate estimation of the IS for any Eu compound. We test this approach on two mixed-valence compounds Eu3S4 and Eu2SiN3, and use it to predict the Y2O3:Eu IS with the result +1.04 mm s−1 at the 24d site and +1.00 mm s−1 at the 8b site.

Nuclear volume isotope fractionation of europium and other lanthanide elements

“…The value of 3.0 eV recommended by the creators of the Eu-pseudopotential used in the present study (Topsakal and Wentzcovitch, 2014) yields a near-metallic electronic structure for crystalline EuO (calculated band gap < 0.1 eV), in contrast to the observed band gap of ~1.1 eV. Setting U = 7.5 eV is consistent with the range of ~6-8 eV used in previous work on Eu(II)-and Eu(III)oxides (e.g., Davydov et al, 2021;Zhang et al, 2014;An et al, 2011;Tong et al, 2014), and yields a more reasonable band gap of ~0.8 eV for EuO. It was not possible to reliably obtain self-consistent electronic structure solutions for Eu 3+ -bearing species with this PAW dataset, so a 4f-in-core pseudopotential from the PSLibrary collection was used instead.…”

“…The most recent estimates, based on Mössbauer spectroscopy, muonic x-ray spectroscopy, and electronic structure calculations, span a slightly narrower range from 0.019-0.025 fm 2 (Kalvius and Shenoy, 1974;Tanaka et al, 1984). Davydov et al (2021) recently calculated a somewhat larger radius change of 0.031 fm 2 , however they used a rough approximation of the ground state 151 Eu charge radius that may affect the estimated radius change in the Mössbauer transition, which makes the accuracy of their estimate difficult to quantify. The mean squared radius difference between 151 Eu (in the 5/2 + ground state) and 153 Eu has been determined to be 0.57-0.61 fm 2 (e.g., Tanaka et al, 1984;Ahmad et al, 1985).…”