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Enhanced thermoelectric response of hole-doped La$_2$NiO$_{4+delta}$ by ab initio calculations

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 Added by Victor Pardo
 Publication date 2012
  fields Physics
and research's language is English




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Thermoelectric properties of the system La$_2$NiO$_{4+delta}$ have been studied ab initio. Large Seebeck coefficient values are predicted for the parent compound, and to some extent remain in the hole-doped metallic phase, accompanied of an increase in the conductivity. This system, due to its layered structure would be a suitable candidate for an improvement of its thermoelectric figure of merit by nanostructurization in thin films, that has already been shown to increase the electrical conductivity ($sigma$). Our calculations show that in the region around La$_2$NiO$_{4.05}$ the system has a large thermopower at high temperatures and also a substantially increased $sigma$. Films grown with this low-doping concentration will show an optimal relationship between thermopower and $sigma$. This result is obtained for various exchange-correlation schemes (correlated, uncorrelated and parameter-free) that we use to analyze the electronic structure of the hole-doped compound.



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Thermoelectric properties of the system La$_2$NiO$_{4+delta}$ have been recently discussed [Phys. Rev. B 86, 165114 (2012)] via ab initio calculations. An optimum hole-doping value was obtained with reasonable thermopower and thermoelectric figure of merit being calculated. Here, a large increase in the thermoelectric performance through lattice strain and the corresponding atomic relaxations is predicted. This increase would be experimentally attainable via growth in thin films of the material on top of different substrates. A small tensile strain would produce large thermoelectric figures of merit at high temperatures, $zT$ $sim$ 1 in the range of oxygen excess $delta$ $sim$ 0.05 - 0.10 and in-plane lattice parameter in the range 3.95 - 4.05 AA. In that relatively wide range of parameters, thermopower values close to 200 $mu$V/K are obtained. The best performance of this compound is expected to occur in the high temperature limit.
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