Semiconducting Heusler Compounds beyond the Slater-Pauling Rule

Heusler compounds with semiconducting properties represent an important class of functional materials. Usually, research on these systems is guided by simple electron-counting rules, such as the Slater-Pauling principle. Here, we report on the discovery of Heusler-type semiconductors, significantly deviating from the Slater-Pauling rule. We theoretically predict the occurrence of nonmagnetic semiconducting ground states in various highly off-stoichiometric full-Heusler alloys, where self-substitution leads to a band-gap opening. This unexpected trend is confirmed experimentally by thermoelectric transport measurements on a multitude of <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mi>Fe</a:mi></a:math><d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:msub><d:mi/><d:mrow><d:mn>2</d:mn><d:mo>−</d:mo><d:mn>2</d:mn><d:mi>x</d:mi></d:mrow></d:msub></d:math><g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:mrow><g:mrow><g:mi mathvariant="normal">V</g:mi></g:mrow></g:mrow></g:math><k:math xmlns:k="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><k:msub><k:mi/><k:mrow><k:mn>1</k:mn><k:mo>−</k:mo><k:mi>x</k:mi></k:mrow></k:msub></k:math><n:math xmlns:n="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><n:mi>Al</n:mi></n:math><q:math xmlns:q="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><q:msub><q:mi/><q:mrow><q:mn>1</q:mn><q:mo>+</q:mo><q:mn>3</q:mn><q:mi>x</q:mi></q:mrow></q:msub></q:math> samples with up to 20% substitution of <t:math xmlns:t="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><t:mi>Fe</t:mi></t:math> and <w:math xmlns:w="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><w:mrow><w:mrow><w:mi mathvariant="normal">V</w:mi></w:mrow></w:mrow></w:math> atoms. The band-gap opening leads to an exceptionally large Seebeck coefficient in <ab:math xmlns:ab="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><ab:mi>p</ab:mi></ab:math>-type <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><db:mi>Fe</db:mi></db:math><gb:math xmlns:gb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><gb:msub><gb:mi/><gb:mn>2</gb:mn></gb:msub></gb:math><jb:math xmlns:jb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><jb:mi>VAl</jb:mi></jb:math> thermoelectrics, previously limited by bipolar conduction and low-density-of-states effective mass. Consequently, our work presents a paradigm to tune the band gap of Heusler compounds by self-substitution and introduces a hitherto unexplored class of semiconductors with exceptional thermoelectric properties, offering significant potential for advancements in energy science and sustainable-energy technologies. Published by the American Physical Society 2024