Thermoelectric properties of Fe and Al double substituted MnSiy (y ~ 1.73)
Résumé
Two series of Fe and Al double substituted MnSiγ chimney ladders with a nominal valence electron count, VEC=14 per transition metal were prepared (γ=1.75). Simultaneous replacement of Mn with Fe and Si with Al yielded the Mn1−xFexSi1.75−xAlx series while the second Mn1−xFexSi1.75–1.75xAl2x series follows the pseudo-binary between MnSi1.75 and FeAl2. Scanning electron microscopy and elemental mapping revealed that ~60% of the nominal Al content ends up in the product with the remainder lost to sublimation, and that up to 7% Al can be substituted in the main group sublattice. Profile analysis of X-ray powder diffraction data revealed gradual changes in the cell metrics, consistent with the simultaneous substitution of Fe and Al in a fixed ratio. All samples are p-type with VEC≈13.95 from the structural data and ~1×1021 holes cm−3 from variable temperature Seebeck measurements. The substituted samples have lower electrical resistivities (ρ300 K=2–5 mΩ cm) due to an improved microstructure. This leads to increased thermoelectric power factors (largest S2/ρ=1.95 mW m−1 K−2) compared to MnSiγ. The thermal conductivity for the Mn0.95Fe0.05Si1.66Al0.1 sample is 2.7 W m−1 K−1 between 300 and 800 K, and is comparable to literature data for the parent material.
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