Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Interstitial-Boron Solution Strengthened WB$_{3+x}$   By means of variable-composition evolutionary algorithm coupled with density
functional theory and in combination with aberration-corrected high-resolution
transmission electron microscopy experiments, we have studied and characterized
the composition, structure and hardness properties of WB$_{3+x}$ ($x$ $<$ 0.5).
We provide robust evidence for the occurrence of stoichiometric WB$_3$ and
non-stoichiometric WB$_{3+x}$ both crystallizing in the metastable $hP$16
($P6_3/mmc$) structure. No signs for the formation of the highly debated WB$_4$
(both $hP$20 and $hP$10) phases were found. Our results rationalize the
seemingly contradictory high-pressure experimental findings and suggest that
the interstitial boron atom is located in the tungsten layer and vertically
interconnect with four boron atoms, thus forming a typical three-center boron
net with the upper and lower boron layers in a three-dimensional covalent
network, which thereby strengthen the hardness.

27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
14
The categories of this paper are: math-ph
5
The categories of this paper are: gr-qc
0
The categories of this paper are: hep-ph
22
The categories of this paper are: chao-dyn
36
The categories of this paper are: cmp-lg
6
The categories of this paper are: astro-ph
13
The categories of this paper are: quant-ph
3
The categories of this paper are: physics
31
The categories of this paper are: ao-sci
33
The categories of this paper are: plasm-ph
29
The categories of this paper are: funct-an
9
The categories of this paper are: nlin
34
The categories of this paper are: chem-ph
19
The categories of this paper are: eess