THE TEMPERATURE-DEPENDENCE OF THE LATTICE-PARAMETERS OF PURE BCC ZR AND BCC ZR-2 AT-PERCENT-CO

The temperature dependence of the lattice parameters in the beta-phase (BCC structure) of pure Zr and Zr-2 at.%Co was determined between 900 and 1550-degrees-C 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 a(Zr) = 3.14(17) x 10(-5) T + 3.579(5) in angstrom (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 fast diffusion of Co in BCC Zr are discussed.