In situ observation of thermal expansion of tetragonal C11b phase in Zr 2Cu (1− x) Pd x alloys

Abstract

The C11b phase crystalline structure (structure type MoSi 2, space group I4/ mmm) in the Zr 2Cu (1− x) Pd x ( x = 0, 0.25, 0.5, 0.75 and 1) alloys was examined in situ using high temperature X-ray diffraction (HTXRD) and Rietveld refinement of the data obtained at a constant heating rate. While the cell volume increases with increasing Pd as expected by the larger atomic radii, the coefficients of thermal expansion (CTEs) do not follow a uniform trend. The bonding in the basal plane is more elastically rigid than along the c-axis for all compositions. The CTE is more anisotropic for Zr 2Pd than for Zr 2Cu, which is consistent with the first-principles calculations that illustrate the rigidity of c-axis relatively to a-axis to be the less for Zr 2Pd. The CTE of the a-axis for Zr 2Pd is in fact negative over the temperature range measured.