Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microstructure and Fe-vacancy ordering in the KFexSe2 superconducting
  system   Structural investigations by means of transmission electron microscopy (TEM)
on KFexSe2 with 1.5 \leq x \leq 1.8 have revealed a rich variety of
microstructure phenomena, the KFe1.5Se2 crystal often shows a superstructure
modulation along the [310] zone-axis direction, this superstructure can be well
interpreted by the Fe-vacancy order within the a-b plane. Increase of
Fe-concentration in the KFexSe2 materials could not only result in the
appearance of superconductivity but also yield clear alternations of
microstructure. Structural inhomogeneity, the complex superstructures and
defect structures in the superconducting KFe1.8Se2 sample have been
investigated based on the high-resolution TEM.

29
The categories of this paper are: funct-an
22
The categories of this paper are: chao-dyn
12
The categories of this paper are: nucl-th
3
The categories of this paper are: physics
20
The categories of this paper are: acc-phys
5
The categories of this paper are: gr-qc
32
The categories of this paper are: atom-ph
19
The categories of this paper are: eess
15
The categories of this paper are: nucl-ex
8
The categories of this paper are: hep-ex
0
The categories of this paper are: hep-ph
9
The categories of this paper are: nlin
1
The categories of this paper are: cs
28
The categories of this paper are: alg-geom
25
The categories of this paper are: patt-sol
27
The categories of this paper are: comp-gas