7,057 research outputs found
High Seebeck coefficient and ultra-low lattice thermal conductivity in Cs2InAgCl6
The elastic, electronic and thermoelectric properties of indium-based
double-perovskite halide, Cs2InAgCl6 have been studied by first principles
study. The Cs2InAgCl6 is found to be elastically stable, ductile, anisotropic
and relatively low hard material. The calculated direct bandgap 3.67 eV by
TB-mBJ functional fairly agrees with the experimentally measured value 3.3 eV
but PBE functional underestimates the bandgap by 1.483 eV. The relaxation time
and lattice thermal conductivity have been calculated by using relaxation time
approximation (RTA) within the supercell approach. The lattice thermal
conductivity (\k{appa}l) is quite low (0.2 Wm-1K-1). The quite low phonon group
velocity in the large weighted phase space, and high anharmonicity (large
phonon scattering) are responsible for small \k{appa}l. The room temperature
Seebeck coefficient is 199 {\mu}VK-1. Such high Seebeck coefficient arises from
the combination of the flat conduction band and large bandgap. We obtain power
factors at 300K by using PBE and TB-mBJ potentials are ~29 and ~31 mWm-1K-2,
respectively and the corresponding thermoelectric figure of merit of Cs2BiAgCl6
are 0.71 and 0.72. However, the maximum ZT value obtained at 700K is ~0.74 by
TB-mBJ potential. The obtained results implies that Cs2InAgCl6 is a promising
material for thermoelectric device applications.Comment: 19 pages. arXiv admin note: text overlap with arXiv:1801.0370
Thermal conductivity in large- two-dimensional antiferromagnets: Role of phonon scattering
Motivated by the recent heat transport experiments in 2D antiferromagnets,
such as LaCuO, where the exchange coupling is larger than the Debye
energy , we discuss different types of relaxation processes for
magnon heat current with a particular focus on coupling to 3D phonons. We study
thermal conductivity by these in-plane magnetic excitations using two distinct
techniques, Boltzmann formalism within the relaxation-time approximation and
memory-function approach. Within these approaches, a close consideration is
given to the scattering of magnons by both acoustic and optical branches of
phonons. A remarkable accord between the two methods with regards to the
asymptotic behavior of the effective relaxation rates is demonstrated.
Additional scattering mechanisms, due to grain boundaries, impurities, and
finite correlation length in the paramagnetic phase, are discussed and included
in the calculations of the thermal conductivity . Again, we
demonstrate a close similarity of the results from the two techniques of
calculating . Our complementary approach strongly suggests that
scattering from optical or zone-boundary phonons is important for magnon heat
current relaxation in a high temperature window of .Comment: 21+ pages, 16 figure
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