EuxSr1-xC2 (0 ≤ x ≤ 1): A Dicarbide Solid Solution with Perfect Vegard Behavior
Résumé
A solid solution EuxSr1-xC2 (0 ≤ x ≤ 1) was synthesized by direct reaction of the elements at 1123 K. The crystal structures of these compounds, investigated by synchrotron powder diffraction, depend upon x. For x > 0.5 the monoclinic ThC2 type structure (C2/c, Z = 4) is observed and for x ≤ 0.5 the ThC2 type structure coexists with the tetragonal CaC2 type structure (I4/mmm, Z = 2). The unit cell volumes per formula unit of all EuxSr1-xC2 compounds show perfect Vegard behaviour, which is due to the almost identical ionic radii of Eu2+ and Sr2+. Mössbauer spectroscopic investigations indeed reveal that Eu is in the divalent state over the whole composition range. EuxSr1-xC2 exhibits several temperature dependent phase transitions that were studied by synchrotron powder diffraction and differential thermal analysis. The transition to a cubic high-temperature modification (Fm-3m, Z = 4) is of special interest, as it contains information about strain effects appearing inside the modifications with ordered C2 dumbbells (ThC2 and CaC2 type structures). The linear temperature dependence of the obtained transition temperatures T(Ph) shows that no observable strain exists in EuxSr1-xC2, which is again due to the almost identical radii of Eu2+ and Sr2+. EuxSr1-xC2 may therefore be described as a strain free dicarbide solid solution with perfect Vegard behaviour.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...