Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Chemical Bond Type, Atom Packing, and Superconductivity of YBa2Cu3O7 and
  NaxWO3   The YBa2Cu3O8-x and NaxWO3 superconductors are treated not as an ionic
compounds but rather as an arrays of atoms featuring both covalent and metallic
bonding. We accept as particle radii the positions of the principal maxima in
the radial distribution functions of the charge density, which are very close
to the known covalent and metallic radii of atoms while differing strongly from
the traditional ionic radii. The graphic pattern of atomic packing in the
lattices reveals a number of features inherent in nonstoichiometric compounds.
The network of atoms Y and Ba in medium Cu-O and of atoms Na in medium WO3 may
be considered not as a dopant but rather as the second component of the
nanocomposite. The scheme of the onset of the superconducting state and
possible methods of its verification are discussed.

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The categories of this paper are: mtrl-th
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The categories of this paper are: hep-lat
3
The categories of this paper are: physics
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The categories of this paper are: ao-sci
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The categories of this paper are: hep-ex
1
The categories of this paper are: cs
2
The categories of this paper are: math
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The categories of this paper are: acc-phys
7
The categories of this paper are: hep-th
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The categories of this paper are: atom-ph
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The categories of this paper are: q-fin
13
The categories of this paper are: quant-ph
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The categories of this paper are: econ
15
The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: patt-sol