Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films

Abstract : A two-step synthesis approach was utilized to grow CaMnO 3 on M-, R-and C-plane sapphire substrates. Radio-frequency reactive magnetron sputtering was used to grow rock-salt-structured (Ca, Mn)O followed by a 3-h annealing step at 800 °C in oxygen flow to form the distorted perovskite phase CaMnO 3. The effect of temperature in the post-annealing step was investigated using x-ray diffraction. The phase transformation to CaMnO 3 started at 450 °C and was completed at 550 °C. Films grown on R-and C-plane sapphire showed similar structure with a mixed orientation, whereas the film grown on M-plane sapphire was epitaxially grown with an out-of-plane orientation in the [202] direction. The thermoelectric characterization showed that the film grown on M-plane sapphire has about 3.5 times lower resistivity compared to the other films with a resistivity of 0.077 Xcm at 500 °C. The difference in resistivity is a result from difference in crystal structure, single orientation for M-plane sapphire compared to mixed for R-and C-plane sapphire. The highest absolute Seebeck coefficient value is-350 lV K-1 for all films and is decreasing with temperature.
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Erik Ekström, Arnaud Le Febvrier, Danièle Fournier, Jun Lu, Vladimir-Lucian Ene, et al.. Formation mechanism and thermoelectric properties of CaMnO3 thin films synthesized by annealing of Ca0.5Mn0.5O films. Journal of Materials Science, Springer Verlag, 2019, 54 (11), pp.8482-8491. ⟨10.1007/s10853-019-03496-7⟩. ⟨hal-02089725⟩

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