Thermoelectric properties of Fe and Al double substituted MnSiγ (γ∼1.73)

Two series of Fe and Al double substituted MnSi gamma chimney ladders with a nominal valence electron count, VEC=14 per transition metal were prepared (gamma=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 similar to 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 approximate to 13.95 from the structural data and similar to 1 x 10(21) holes cm(-3) from variable temperature Seebeck measurements. The substituted samples have lower electrical resistivities (rho(300 K)=2-5 m Omega cm) due to an improved microstructure. This leads to increased thermoelectric power factors (largest S-2/rho=1.95 mW m(-1) K-2) compared to MnSi gamma. The thermal conductivity for the Mn0.95Fe0.05Si1.66Al0.1 sample is 2.7W m(-1) K-1 between 300 and 800 K, and is comparable to literature data for the parent material. (C) 2015 The Authors. Published by Elsevier Inc.