Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: A simple model for vacancy order and disorder in defective half-Heusler
  systems   Defective half-Heusler systems X(1-x)YZ with large amounts of intrinsic
vacancies, such as Nb(1-x)CoSb, Ti(1-x)NiSb and V(1-x)CoSb, are a group of
promising thermoelectric materials. Even with high vacancy concentrations they
maintain the average half-Heusler crystal structure. These systems show high
electrical conductivity but low thermal conductivity arising from an ordered YZ
lattice, which conducts electrons, while the large amounts of vacancies on the
X sublattice effectively scatters phonons. Using electron scattering it was
recently observed that in addition to Bragg diffraction from the average cubic
half-Heusler structure, some of these samples show broad diffuse scattering
indicating short-range vacancy order while other samples show sharp additional
peaks, indicating long-range vacancy ordering. Here we show that both the short
and long-range ordering can be explained using the same simple model, which
assumes that vacancies on the X-sublattice avoid each other. The samples
showing long-range vacancy order are in agreement with the predicted
ground-state of the model, while short-range order samples are quenched
high-temperature states of the system. A previous study showed that changes in
sample stoichiometry affect whether the short or long-range vacancy structure
is obtained, but the present model suggests that thermal treatment of samples
should allow controlling the degree of vacancy order, and thereby the thermal
conductivity, without changes in composition. This is important as the
composition also dictates the amount of electrical carriers. Independent
control of electrical carrier concentration and degree of vacancy order should
allow further improvements in the thermoelectric properties of these systems.

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The categories of this paper are: hep-ph
27
The categories of this paper are: comp-gas
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
26
The categories of this paper are: bayes-an
35
The categories of this paper are: mtrl-th
10
The categories of this paper are: q-bio
24
The categories of this paper are: dg-ga
8
The categories of this paper are: hep-ex
30
The categories of this paper are: q-alg
11
The categories of this paper are: hep-lat
3
The categories of this paper are: physics
29
The categories of this paper are: funct-an
15
The categories of this paper are: nucl-ex
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin