Electronic structure and transport properties of SrAl2Si2: Effect of yttrium substitution

We report the results of yttrium substitution on the electrical resistivity (ρ), the thermal conductivity (κ), as well as the Seebeck coefficient (S) of the Sr1−xYxAl2Si2 alloys with 0 ≤ x ≤ 0.20. Both ρ(T) and S(T) data suggest that SrAl2Si2 is a semimetallic, low charge carrier density system with a pseudogap at the Fermi level density of states (DOS). Upon substituting Y onto the Sr sites, the electrical resistivity and the absolute value of the Seebeck coefficient decrease significantly. Such an observation can be associated with the modification of the electronic band structure due to electron doping via Y substitution. Analysis of the thermal conductivity reveals the contribution of various thermal scattering mechanisms through chemical substitution. Theoretical studies with density functional theory are also employed to investigate the electronic band structure of Sr1−xYxAl2Si2. It is revealed that SrAl2Si2 possesses a shallow DOS at the Fermi level with both n-type and p-type charge carriers. Upon Y substitution a shift in the Femi level occurs such that the Sr1−xYxAl2Si2 system becomes more metallic with increasing x, being consistent with the experimental findings.