Search NASA⌕ Search

Engineering topics

Adeleke, Adebayo A.

Publications and source records attributed to Adeleke, Adebayo A..

4 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Two good metals make a semiconductor: A potassium-nickel compound under pressure

We predict a potassium-nickel intermetallic compound K 2 Ni at high pressure and identify it as the long-sought structure of the only known K-Ni compound to date. Although both constituent elements are metallic, K 2 Ni exhibits a semiconducting ground state with an indirect band gap of 0.65 eV. Electron instability due to the degeneracy at the Fermi level arises from the particular motif of the structure, which in turn induces symmetry-breaking Peierls distortion and a nonmetallic ground state. Overall, the results indicate that the chemical properties of elements can change dramatically under extreme conditions and have significant implications for the postulation that potassium is incorporated in Earth's core.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Nitrogen in black phosphorus structure

Group V elements in crystal structure isostructural to black phosphorus with unique puckered two-dimensional layers exhibit exciting physical and chemical phenomena. However, as the first element of group V, nitrogen has never been found in the black phosphorus structure. Here, we report the synthesis of the black phosphorus–structured nitrogen at 146 GPa and 2200 K. Metastable black phosphorus–structured nitrogen was retained after quenching it to room temperature under compression and characterized in situ during decompression to 48 GPa, using synchrotron x-ray diffraction and Raman spectroscopy. We show that the original molecular nitrogen is transformed into extended single-bonded structure through gauche and trans conformations. Raman spectroscopy shows that black phosphorus–structured nitrogen is strongly anisotropic and exhibits high Raman intensities in two A g normal modes. Synthesis of black phosphorus–structured nitrogen provides a firm base for exploring new type of high-energy-density nitrogen and a new direction of two-dimensional nitrogen.

58 GEOSCIENCES↗