Pressure-induced boron clathrates with ambient-pressure superconductivity

Abstract

Elementary B in binary metal borides forms varied polymetric configurations due to its electron-deficient nature. Here we predict a new pressure-stabilized boron clathrate structure, LaB8, that is recoverable to ambient...

Prediction of novel boron–carbon based clathrates

“…Although both of them have negative formation enthalpy with respect to the pure elemental substances, 19,[43][44][45][46] they are metastable compounds compared with the energetically favorable binary and ternary phases. 19,22,[47][48][49][50][51] According to the different synthesis routes as listed in Tables S2 and S3 (ESI †), most compounds have formation enthalpies less than 50 meV per atom that is within the range of experimental synthesis (B50 meV). 52 For SrB 2 C 4 , the synthesis route with SrB 2 and diamond/ graphite carbon as reactants exhibits a negative formation enthalpy of À31.6/À289.2 meV per atom at 50 GPa.…”

Unveiling the influence of the boron clathrate lattice on superconductivity in a ternary Mg–La–B system

“…1a and b show the ternary phase diagram of the Mg–La–B system focusing on B-rich species at 0 and 50 GPa, respectively. The diagrams were constructed based on the formation energy calculations, considering the stable elements, binary Mg–La, 52 Mg–B, 53 and La–B 54 compounds, and newly predicted ternary compounds. To facilitate a more comprehensive visualization, we have provided a 3D convex hull in Fig.…”

“…Together with the electronic property analysis, we conclude that the strong coupling between s electrons and the vibrational modes of the boron clathrate lattice plays a pivotal role in the superconductivity in MgLaB 10 . The T c of MgLaB 10 is higher than those of most boron clathrates under ambient pressure, such as LaB 8 (14.0-19.6 K), 30,31 CaB 7 (7.7 K) 32 and LiLaB 8 (9.5 K) 33 (Table S4, ESI †), attributed to its high boronderived density of DOSs at the Fermi level and the strong EPC effect. MgLaB 10 exhibts a lower superconductivity compared to MgB 2 23,70 and SrB 3 C 3 , 21,[71][72][73] primarily due to the lack of significant phonon softening at the G point associated with caged boron.…”

“…[26][27][28][29] Analogous to the hydrogen clathrate, the boron clathrate exhibits a strong EPC, thereby fostering superconductivity. Several boron clathrate-based superconductors have been proposed, including LaB 8 with a B 26 cage, 30,31 CaB 7 with a B 23 cage, 32 and LiLaB 8 with B 12 and B 24 cages, 33 exhibiting T c s in the range of 8-20 K under ambient pressure conditions. All of these indicate that boron clathrate compounds may hold great promise as potential superconductors.…”

Discovery of superconductivity in technetium borides at moderate pressures

“…15 At present, the discovered bulk superconducting borides with the same stoichiometry as MgB 2 include CaB 2 ( T c ∼ 50 K 16 or 9.4–28.6 K 17 at ambient pressure, theory), NbB 2 ( T c ∼ 9.2 K at ambient pressure, experiment 18–20 ), OsB 2 ( T c = 2.1 K at ambient pressure, experiment 21 ), RuB 2 ( T c = 1.6 K at ambient pressure, experiment 21 ), ScB 2 ( T c = 1.5 K at ambient pressure, experiment 22 ), WB 2 (maximum T c = 15 K at 100 GPa, experiment 23 ), ZrB 2 ( T c = 5.5 K at ambient pressure, experiment 24 ), SiB 2 ( T c = 21 K at ambient pressure, theory 25 ) and MoB 2 ( T c = 32 K at 100 GPa, experiment 26 ). Superconducting borides with other stoichiometries include X 7 B 3 (X = Re and Ru with T c = 3.3 and 2.6 K, respectively, at ambient pressure, experiment 27,28 ), Re 3 B ( T c = 4.8 K at ambient pressure, experiment 28 ), X 2 B (X = Mo, Re, Ta and W with T c = 5.1, 2.8, 3.1 and 3.2 K, respectively, at ambient pressure, experiment 27 ), XB (X = Hf, Nb, Mo, Ta and Zr with T c = 3.1, 8.3, 0.5, 4.0 and 2.8–3.4 K, respectively, at ambient pressure, experiment 27 ), FeB 4 ( T c = 2.9 K at ambient pressure, theory and experiment 29,30 ), XB 5 (X = Na, K, Rb, Ca, Sr, Ba, Sc and Y with T c = 17.5, 14.7, 18.6, 6.6, 6.8, 16.3, 14.2 and 12.3 K, respectively, at ambient pressure, theory 31 ), BeB 6 ( T c = 24 K at 4 GPa, theory 32 ), CB 6 ( T c = 12.5 K at ambient pressure, theory 33 ), MgB 6 ( T c = 9.5 K at 32.6 GPa, theory 34 ), ScB 6 (in P 2 1 / m -, C 2/ m - and Cmcm -structure with T c = 5.8 K at ambient pressure, 2.2 K at 500 GPa, and 2.6 K at 800 GPa, respectively, theory 35 ), XB 6 (X = Nb, La, Th and Y with T c = 3.0, 5.7, 0.74 and 7.1 K, respectively, at ambient pressure, experiment 27 ), XB 7 (X = Li, Na, K, Mg, Ca and Sr with T c = 21.6, 18.3, 26.2, 29.3, 7.7 and 12.7 K, respectively, at ambient pressure, theory 36 ), RbB 6 and RbB 8 ( T c = 7.3–11.6 K and 4.8–7.5 K at ambient pressure, respectively, theory 37 ), YB 6 ( T c = 7.2 K at ambient pressure, experiment 38 ), LaB 8 ( T c = 14 K 39 or 20 K 40 at ambient pressure, theory), XB 12 (X = Nb, La, Th, Y and Zr with T c = 3.0, 5.7, 0.74, 7.1 and 5.8 K, respectively, at ambient pressure, experiment 27,41–43 ), ternary borides like SrB 3 C 3 ( T c = 22 K at 23 GPa, theory and experiment 44 ), or even quaternary borides RbYbB 6 C 6 and RbBaB 6 C 6 (both with T c ≈ 71 K at ambient pressure, theory 45 ).…”