The temperature dependence of the lattice parameters of pure BCC Zr and BCC Zr-2 at.%Co

The temperature dependence of the lattice parameters in the β-phase (BCC structure) of pure Zr and Zr-2 at.%Co was determined between 900 and 1550oC by neutron diffraction. All diffraction patterns show a high diffuse background, which is identified as thermal diffuse scattering and originates from particular low-energy phonons in BCC Zr and its alloys. The lattice parameter of pure BCC Zr is given by aZr = 3.14(17)x10-5T+3.579(5) in A (T in K). Alloying with Co results in a contraction of BCC Zr, from which it is concluded that Co is dissolved substitutionally. The consequences of these results for the last diffusion of Co in BCC Zr are discussed. (author)