Re-investigation of the Cd-Ce phase diagram and structural characterization of the high-temperature phase Cd_17+2xCe_2-x (x ~ 0.02)

The complete Cd-Ce equilibrium phase diagram was investigated with a combination of powder-XRD, SEM and DTA. The presence of seven intermetallic compounds, i.e., CdCe, Cd2Ce, Cd3Ce, Cd58Ce13, Cd6Ce (resp. Cd37Ce6), Cd17Ce2 and Cd11Ce, reported previously in literature, was confirmed. A polymorphic transformation of Cd2Ce into a high-temperature modification was indicated to occur at 871 °C at the respective stoichiometric composition. The homogeneity range of both the low (γ) and high-temperature (δ) allotropic modification of Ce could be determined precisely and a limited solubility of 2.5 as well as 17 at.% Cd was derived. In addition, liquidus temperatures and all invariant reactions were examined by thermal analyses. One eutectoid reaction at 421 °C and ~15 at.% Cd as well as four eutectic reactions at ~20 at.% Cd (646 °C), 56 at.% Cd (910 °C), 77.5 at.% Cd (857 °C) and close to 100 at.% Cd (320 °C) were detected. One peritectoid reaction at 852 °C and three peritectic reactions at 730, 610 and 605 °C were recorded. Moreover, single-crystal x-ray diffraction was employed, and a complete description of the structure of Cd17+2x Ce2−x (x ~ 0.02) is given with focus on the correct defect mechanism. It turned out that vacancy formation on one of the Ce sites (Ce1) is compensated by 2 Cd atoms on Cd sites (Cd5) very close by