Structural and thermodynamic data on the pseudobinary phases R(Co 1− xCu x) 5 WITH R ≡ Sm, Y, Ce

Abstract

For the phases R(Co 1−itxCu itx) 5 with R ≡ Sm, Y, Ce, homogenized at 950 °C, the enthalpies of formation were determined by a calorimetry technique involving dissolution in molten tin and the lattice parameters were measured using X-ray diffraction in a focusing camera. In order to study the effect of substitution of cobalt for copper, the lattice parameters were corrected for the contribution of the departure of R from stoichiometry. For the R(Co 1−itxCu itx) 5 phases with R ≡ Sm, Y, the lattice parameters were also measured after heat treatment at 400 °C. The x dependences of the enthalpies of formation and lattice parameters indicate an ideal behaviour for the mixing of SmCo 5 and SmCu 5 on one hand, and for YCo 5 and YCu 5 on the other hand. This result is consistent with the homogeneous state found for Sm(Co 1−itxCu itx) 5 and Y(Co 1−itxCu itxon the whole x range at 400 °C. For the mixture of CeCo 5 and CeCu 5, the enthalpies of formation exhibit a slightly positive deviation which predicts the solid state miscibility gap previously evidenced in the CeCo 5-CeCu 5 section below 800 °C.