Effect of annealing on the structure of an amorphous(Mo0.6Ru0.4)82B18alloy

Abstract

The amorphous metallic glass ${({\mathrm{Mo}}_{0.6}{\mathrm{Ru}}_{0.4})}_{82}$${\mathrm{B}}_{18}$ was annealed for various lengths of time at temperatures up to 650\ifmmode^\circ\else\textdegree\fi{}C. The changes in structure due to these annealing treatments were determined by measurements of superconducting properties (${T}_{c}$,${B}_{c2}$,${J}_{c}$), electrical resistivity (${\ensuremath{\rho}}_{n}$), low-temperature specific heat (electronic coefficient $\ensuremath{\gamma}$), small-angle x-ray scattering (SAXS), and transmission electron microscopy (TEM). At lower annealing temperatures (\ensuremath{\le}450\ifmmode^\circ\else\textdegree\fi{}C) only small changes occurred in the composition-dependent parameters (${T}_{c}$,$\ensuremath{\gamma}$) but large degradations were exhibited in those quantities (${J}_{c}$, fracture strain) sensitive to the defect structure. No evidence of microstructural changes was revealed by SAXS or TEM in this regime. At higher annealing temperatures (or longer times) evidence for the development of, first, phase separation, then, the beginnings of crystallization was found by SAXS and TEM. In this regime larger degradations of ${T}_{c}$ and $\ensuremath{\gamma}$ occurred along with a change in the form of the ${F}_{p}(b)$ curve (i.e., a change in the fluxoid pinning mechanism). The above observations imply annealing-induced long-range compositional variations. The activation energy for the onset of long-range compositional inhomogeneity was determined to be 309 kJ ${\mathrm{mol}}^{\ensuremath{-}1}$ (3.2 eV).