Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Critical mode and band-gap-controlled bipolar thermoelectric properties
  of SnSe   The reliable calculation of electronic structures and understanding of
electrical properties depends on an accurate model of the crystal structure.
Here, we have reinvestigated the crystal structure of the high-zT
thermoelectric material tin selenide, SnSe, between 4 and 1000 K using
high-resolution neutron powder diffraction. Symmetry analysis reveals the
presence of four active structural distortion modes, one of which is found to
be active over a relatively wide range of more than +/-200 K around the
symmetry-breaking Pnma-Cmcm transition at 800 K. Density functional theory
calculations on the basis of the experimental structure parameters show that
the unusual, step-like temperature dependencies of the electrical transport
properties of SnSe are caused by the onset of intrinsic bipolar conductivity,
amplified and shifted to lower temperatures by a rapid reduction of the band
gap between 700 and 800 K. The calculated band gap is highly sensitive to small
out-of-plane Sn displacements observed in the diffraction experiments. SnSe
with a sufficiently controlled acceptor concentration is predicted to produce
simultaneously a large positive and a large negative Seebeck effect along
different crystal directions.

35
The categories of this paper are: mtrl-th
15
The categories of this paper are: nucl-ex
25
The categories of this paper are: patt-sol
0
The categories of this paper are: hep-ph
32
The categories of this paper are: atom-ph
28
The categories of this paper are: alg-geom
30
The categories of this paper are: q-alg
17
The categories of this paper are: q-fin
23
The categories of this paper are: solv-int
2
The categories of this paper are: math
18
The categories of this paper are: econ
14
The categories of this paper are: math-ph
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
36
The categories of this paper are: cmp-lg
34
The categories of this paper are: chem-ph