Distinctive electronic characteristics and ultra-high thermoelectric power factor of Be–Fe intermetallics

Abstract

Beryllium (Be) alloys are indispensable in cutting-edge applications owing to their unique advantages. However, the scientific understanding of their structure and property is inadequate, which greatly restricts their applications within a narrow field. In this work, a systematic investigation of the structure and properties of a Be–Fe binary alloy was carried out with first-principles unbiased evolutionary algorithms. Five new intermetallics unreported before, including insulating Be₁₁Fe and Be₄Fe, metallic Be₃Fe, and metastable BeFe and BeFe₂, were discovered, among which Be₁₁Fe has a unique clathrate structure and is an electride. Surprisingly, we found that Fe unexpectedly acts as an anion in all known Be–Fe intermetallics, and its valence state can even reach −5, leading to the complete filling of its 3d orbitals. Most of these compounds exhibit a gap or pseudogap at the Fermi level. Specifically, the band gap is determined as 0.22 eV and 0.85 eV for Be₁₁Fe and Be₄Fe, respectively, at the level of single-shot GW. This is the first report on insulating phases in Be-based intermetallics. We also discovered that Be₁₁Fe exhibits an impressive thermoelectric power factor of 178 μW cm⁻¹ K² at room temperature; to our best knowledge, this is the highest among known semiconductors under ambient conditions, indicating its potential for waste heat harvesting and active cooling. These findings will deepen our understanding of Be-based and Fe-based compounds and expand the application fields of Be-based alloys to a brand-new realm.