Strain-induced enhancement of the thermoelectric power in thin films of hole-doped La2NiO4+δ

P L Bach,Elías Ferreiro-Vila,B Rodríguez-González,V Leborán,J M Vila-Fungueiriño,F Rivadulla

doi:10.1063/1.4818356

P L Bach, Elías Ferreiro-Vila + Show 4 more

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https://doi.org/10.1063/1.4818356

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Abstract

We propose a novel route for optimizing the thermoelectric power of a polaronic conductor, independent of its electronic conductivity. This mechanism is exemplified here in thin-films of La2NiO4+δ. Tensile stress induced by epitaxial growth on SrTiO3 doubles the thermoelectric power of ≈15 nm thick films relative to ≈90 nm films, while the electronic conductivity remains practically unchanged. Epitaxial strain influences the statistical contribution to the high temperature thermopower, but introduces a smaller correction to the electronic conductivity. This mechanism provides a new way for optimizing the high temperature thermoelectric performance of polaronic conductors.

Highlights

Lanthanum nickelate, La2NiO4, crystallizes in the 2D-K2NiF4 structure, in common with several cuprate high-temperature superconductors
Pardo et al.[6] suggested that the thermoelectric power factor (S2/ρ) is optimized for La2NiO4.05, and suggested that this performance might be further enhanced by increasing the lattice parameter, via epitaxial strain in a film.[7]
The outof-plane lattice parameter expands as a function of thickness (Figure 1), confirming the relaxation of the stress induced by epitaxial growth in the ab-plane (Figure 2)

Summary

Introduction

La2NiO4, crystallizes in the 2D-K2NiF4 structure, in common with several cuprate high-temperature superconductors. We report the effect of tensile stress on the thermoelectric power and electrical resistivity of La2NiO4+δ thin films. Our results demonstrate that the thermoelectric power in the films can be manipulated by epitaxial stress, independently of the electrical resistivity.

Results

Conclusion