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Structure searches and superconductor discovery in XB₂ (X = Sc, Ti, V, Cr, and Tc).

ABSTRACT: With extensive structure searches for XB₂ (X = Sc, Ti, V, Cr, and Tc) under pressures up to 100 GPa, we uncovered that the crystal structures of these compounds with the lowest enthalpy have the same space group (P6/mmm) as MgB₂ at ambient pressure. Among them, ScB₂, TiB₂ and VB₂ are dynamically stable at ambient pressure, but they do not superconduct. CrB₂ becomes dynamically stable at 108 GPa and shows superconductivity with a transition temperature (T_c) of 26.0 K. TcB₂ is not dynamically stable until 9 GPa. At 20 GPa, it has a T_c of 23.5 K. Further calculations indicate that CrB₂ and TcB₂ are also thermodynamically stable, suggesting that it is highly likely that they can be synthesized successfully in the laboratory. We found that transition metal atoms (Cr/Tc) dominate soft phonon vibrations and make significant contributions to the electron-phonon coupling (EPC) and superconductivity in CrB₂/TcB₂, which is in strong contrast to the case of MgB₂, where high-frequency B vibrations dominate the EPC and superconductivity. Our work enriches the understanding of superconductivity in transition metal borides.

SUBMITTER: Meng J

PROVIDER: S-EPMC10985594 | biostudies-literature | 2024 Mar

REPOSITORIES: biostudies-literature

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Structure searches and superconductor discovery in XB2 (X = Sc, Ti, V, Cr, and Tc).

Meng Jingjing J Zheng Pengyu P Peng Yiran Y Liu Rui R Yang Ying Y Yin Zhiping Z

RSC advances 20240301 15

With extensive structure searches for XB2 (X = Sc, Ti, V, Cr, and Tc) under pressures up to 100 GPa, we uncovered that the crystal structures of these compounds with the lowest enthalpy have the same space group (P6/mmm) as MgB2 at ambient pressure. Among them, ScB2, TiB2 and VB2 are dynamically stable at ambient pressure, but they do not superconduct. CrB2 becomes dynamically stable at 108 GPa and shows superconduct ...[more]

PMID: 38567342

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Project description:A theoretical study of geometrical structures, electronic properties, and spectral properties of single-atom transition metal-doped boron clusters MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) is performed using the CALYPSO approach for the global minimum search, followed by density functional theory calculations. The global minima obtained for the MB24 - (M = Sc, Ti, V, and Cr) clusters correspond to cage structures, and the MB24 - (M = Mn, Fe, and Co) clusters have similar distorted four-ring tubes with six boron atoms each. Interestingly, the global minima obtained for the NiB24 - cluster tend to a quasi-planar structure. Charge population analyses and valence electron density analyses reveal that almost one electron on the transition-metal atoms transfers to the boron atoms. The electron localization function (ELF) of MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) indicates that the local delocalization of MB24 - (M = Sc, Ti, V, Cr, and Ni) is weaker than that of MB24 - (M = Mn, Fe, and Co), and there is no obvious covalent bond between doped metal and B atoms. The spin density and spin population analyses reveal that open-shell MB24 - (M = Ti, Cr, Fe, and Ni) has different spin characteristics which are expected to lead to interesting magnetic properties and potential applications in molecular devices. The polarizability of MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) shows that MB24 - (M = Mn, Fe, and Co) has larger first hyperpolarizability, indicating that MB24 - (M = Mn, Fe, and Co) has a strong nonlinear optical response. Hence, MB24 - (M = Mn, Fe, and Co) might be considered as a promising nonlinear optical boron-based nanomaterial. The calculated spectra indicate that MB24 - (M = Sc, Ti, V, Cr, Mn, Fe, Co, and Ni) has different and meaningful characteristic peaks that can be compared with future experimental values and provide a theoretical basis for the identification and confirmation of these single-atom transition metal-doped boron clusters. Our work enriches the database of geometrical structures of doped boron clusters and can provide an insight into new doped boron clusters.

Dataset Information

Structure searches and superconductor discovery in XB₂ (X = Sc, Ti, V, Cr, and Tc).

Publications

Structure searches and superconductor discovery in XB<sub>2</sub> (X = Sc, Ti, V, Cr, and Tc).

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