101. The effects of microstructure, Nb content and secondary Ruddlesden-Popper phase on thermoelectric properties in perovskite CaMn 1- x Nb x O 3 ( x = 0-0.10) thin films.
- Author
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Ekström E, le Febvrier A, Bourgeois F, Lundqvist B, Palisaitis J, Persson POÅ, Caballero-Calero O, Martín-González MS, Klarbring J, Simak SI, Eriksson F, Paul B, and Eklund P
- Abstract
CaMn
1- x Nbx O3 ( x = 0, 0.5, 0.6, 0.7 and 0.10) thin films have been grown by a two-step sputtering/annealing method. First, rock-salt-structured (Ca,Mn1- x ,Nbx )O thin films were deposited on 11̄00 sapphire using reactive RF magnetron co-sputtering from elemental targets of Ca, Mn and Nb. The CaMn1- x Nbx O3 films were then obtained by thermally induced phase transformation from rock-salt-structured (Ca,Mn1- x Nbx )O to orthorhombic during post-deposition annealing at 700 °C for 3 h in oxygen flow. The X-ray diffraction patterns of pure CaMnO3 showed mixed orientation, while Nb-containing films were epitaxially grown in [101] out of-plane-direction. Scanning transmission electron microscopy showed a Ruddlesden-Popper (R-P) secondary phase in the films, which results in reduction of the electrical and thermal conductivity of CaMn1- x Nbx O3 . The electrical resistivity and Seebeck coefficient of the pure CaMnO3 film were measured to 2.7 Ω cm and -270 μV K-1 at room temperature, respectively. The electrical resistivity and Seebeck coefficient were reduced by alloying with Nb and was measured to 0.09 Ω cm and -145 μV K-1 for x = 0.05. Yielding a power factor of 21.5 μW K-2 m-1 near room temperature, nearly eight times higher than for pure CaMnO3 (2.8 μW K-2 m-1 ). The power factors for alloyed samples are low compared to other studies on phase-pure material. This is due to high electrical resistivity originating from the secondary R-P phase. The thermal conductivity of the CaMn1- x Nbx O3 films is low for all samples and is the lowest for x = 0.07 and 0.10, determined to 1.6 W m-1 K-1 . The low thermal conductivity is attributed to grain boundary scattering and the secondary R-P phase., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)- Published
- 2020
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