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Title: Amorphous tantala and its relationship with the molten state

The structure factors of molten Ta 2O 5 and Nb 2O 5 have been measured by high-energy x-ray and pulsed neutron diffraction. These are compared to transmission-mode x-ray diffraction through a self-supported 15-μm ion-beam sputtered amorphous tantala film. Atomistic models derived from the diffraction data by means of empirical potential structure refinement reveal that tantala and niobia liquids are very close to isomorphous, as confirmed by measurement of a molten mixture, Ta 0.8Nb 1.2O 5. Nonetheless, peak Nb-O bond lengths are about 1% shorter than those for Ta-O, at temperatures, T*=T/T melt, scaled to the melting points. Mean coordination numbers are n MO≃5.6(1),n OM≃2.23(4) in the liquid state, and n TaO≃6.6(2),n OTa≃2.63(8) in the solid. The liquids are built from five- and six-fold M-O polyhedra which connect principally by corner sharing, with a minority of edge sharing; a-Ta 2O 5 on the other hand has a local structure more akin to the crystalline polymorphs, built primarily from six- and seven-fold polyhedra, with a larger degree of edge sharing. The structural differences between liquid and amorphous Ta 2O 5, coupled with observations of increasing peak bond lengths upon cooling, are consistent with the interpretation that the amorphous film reaches a supercooledmore » liquidlike metastable equilibrium during deposition. In other words, the amorphous film shares a common progenitor state with a hypothetical glass quenched from a fragile melt. In addition, we show that recent classical interatomic potentials do not fully reproduce the diffraction data, and infer that inclusion of attractive (non-Coulombic) Ta-Ta interactions is important, particularly for obtaining the correct degree of edge sharing, coordination numbers, and densities. In conclusion, nanoscale inhomogeneity of the amorphous film is confirmed by the observation of small-angle x-ray scattering.« less
Authors:
 [1] ;  [2] ; ORCiD logo [3] ;  [4] ;  [4] ;  [4] ;  [5] ;  [1]
  1. Materials Development, Inc., Arlington Heights, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS), X-Ray Science Division
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS), X-Ray Science Division
  3. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division
  4. Univ. de Lyon, France, Villeurbanne (France). Inst. Lumiere Matiere
  5. Materials Development, Inc., Arlington Heights, IL (United States)
Publication Date:
Grant/Contract Number:
AC05-00OR22725; SC0015241; AC02-06CH11357
Type:
Accepted Manuscript
Journal Name:
Physical Review Materials
Additional Journal Information:
Journal Volume: 2; Journal Issue: 4; Journal ID: ISSN 2475-9953
Publisher:
American Physical Society (APS)
Research Org:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY
OSTI Identifier:
1436942
Alternate Identifier(s):
OSTI ID: 1434346