title: Local structure, composition, and crystallization mechanism of a model two-phase "composite nanoglass".
abstract: We report a detailed study of the local composition and structure of a model, bi-phasic nanoglass with nominal stoichiometry Cu55Nb45. Three dimensional atom probe data suggest a nanoscale-phase-separated glassy structure having well defined Cu-rich and Nb-rich regions with a characteristic length scale of ≈ 3 nm. However, extended x-ray absorption fine structure analysis indicates subtle differences in the local environments of Cu and Nb. While the Cu atoms displayed a strong tendency to cluster and negligible structural order beyond the first coordination shell, the Nb atoms had a larger fraction of unlike neighbors (higher chemical order) and a distinctly better-ordered structural environment (higher topological order). This provides the first experimental indication that metallic glass formation may occur due to frustration arising from the competition between chemical ordering and clustering. These observations are complemented by classical as well as ab initio molecular dynamics simulations. Our study indicates that these nanoscale phase-separated glasses are quite distinct from the single phase nanoglasses (studied by Gleiter and others) in the following three respects: (i) they contain at least two structurally and compositionally distinct, nanodispersed, glassy phases, (ii) these phases are separated by comparatively sharp inter-phase boundaries, and (iii) thermally induced crystallization occurs via a complex, multi-step mechanism. Such materials, therefore, appear to constitute a new class of disordered systems that may be called a composite nanoglass.
authors.affiliation: CSRRI-IIT, MRCAT, Sector 10, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Soma
authors.initials: S
authors.lastname: Chattopadhyay
authors.affiliation: EXAFS Analysis, Bolingbrook, Illinois 60440, USA.
authors.forename: S D
authors.initials: SD
authors.lastname: Kelly
authors.affiliation: CSRRI-IIT, MRCAT, Sector 10, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: Tomohiro
authors.initials: T
authors.lastname: Shibata
authors.affiliation: Sector 20 XOR, Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA.
authors.forename: M
authors.initials: M
authors.lastname: Balasubramanian
authors.affiliation: Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203-5017, USA.
authors.forename: S G
authors.initials: SG
authors.lastname: Srinivasan
authors.affiliation: Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203-5017, USA.
authors.forename: Jincheng
authors.initials: J
authors.lastname: Du
authors.affiliation: Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203-5017, USA.
authors.forename: Rajarshi
authors.initials: R
authors.lastname: Banerjee
authors.affiliation: Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research, Mumbai 400005, India.
authors.forename: Pushan
authors.initials: P
authors.lastname: Ayyub