Unexpected p-type thermoelectric transport arising from magnetic Mn substitution in Fe₂V₁₋ₓMnₓAl Heusler compounds

Abstract

p-Type Fe2VAl-based thermoelectrics have been much less investigated compared to their respective n-type counterparts. Thus, it is crucial to identify novel doping strategies to realize enhanced p-type Fe2VAl Heusler compounds. In the current study, the effect of Mn substitution in Fe2V1xMnxAl is investigated with respect to temperature-dependent electronic transport as well as temperature- and field-dependent magnetic properties. We find an anomalous and unexpected p-type Seebeck coefficient for nominally n-doped Fe2V1xMnxAl over an extremely large range of concentrations up to x = 0.6. Using density functional theory (DFT) calculations, this is traced back to distinct modifications of the electronic structure, i.e., localized magnetic defect states (m = 2.43mB) at the valence and conduction band edges, and a concomitant pinning of the Fermi level within the pseudogap. Furthermore, we were able to further optimize the thermoelectric properties by co-doping Al antisites in off-stoichiometric Fe2V0.9Mn0.1Al1+y, yielding sizeable values of the power factor, PF = 2.2 mW K2 m1 in Fe2V0.9Mn0.1Al1.1 at 350 K, and figure of merit, ZT B 0.1 for highly off-stoichiometric Fe2V0.9Mn0.1Al1.5 at T = 500 K. Our work underlines the prospect of engineering Fe2VAl-based Heusler compounds via magnetic doping to realize enhanced p-type thermoelectris and encourages studies involving other types of cosubstitution for Mn-substituted Fe2V1xMnxAl