Eu x Sr 1– x C 2 (0 ≤ x ≤ 1): A Dicarbide Solid Solution with Perfect Vegard Behavior

A solid solution Eu x Sr 1 – x C 2 (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 ThC 2 type structure ( C 2/ c , Z = 4) is observed and for x ≤ 0.5 the ThC 2 type structure coexists with the tetragonal CaC 2 type structure ( I 4/ mmm , Z = 2). The unit cell volumes per formula unit of all Eu x Sr 1 – x C 2 compounds show perfect Vegard behavior, which is due to the almost identical ionic radii of Eu 2+ and Sr 2+ . Mössbauer spectroscopic investigations indeed reveal that europium is in the divalent state over the whole composition range. Eu x Sr 1– x C 2 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 m , Z = 4) is of special interest, as it contains information about strain effects appearing inside the modifications with ordered C 2 dumbbells (ThC 2 and CaC 2 type structures). The linear temperature dependence of the obtained transition temperatures T Ph shows that no observable strain exists in Eu x Sr 1– x C 2 , which is again due to the almost identical radii of Eu 2+ and Sr 2+ . Eu x Sr 1– x C 2 may therefore be described as a strain free dicarbide solid solution with perfect Vegard behavior.