Prediction of phonon-mediated superconductivity in new Ti-based M$$_2$$AX phases

Abstract

A high-throughput computational method is used to predict 39 new superconductors in the Ti-based M$$_2$$ 2 AX phases, and the best candidates are then studied in more detail using density functional theory electron–phonon coupling calculations. The detailed calculations agree with the simple predictions, and Ti$$_2$$ 2 AlX (X: B, C and N) materials are predicted to have higher values of $$T_c$$ T c than any currently known hexagonal M$$_2$$ 2 AX phases. The electronic states at the Fermi level are dominated by the Ti 3d states. The choice of X (X: B, C and N) has a significant impact on the electronic density of states but not on the phonon characteristics. The electron–phonon coupling parameter for Ti$$_2$$ 2 AlX (X: B, C and N) was determined to be 0.685, 0.743 and 0.775 with a predicted $$T_c$$ T c of 7.8 K, 10.8 K and 13.0 K, respectively.

Does Cr2AlN Have the Highest Possible Superconducting Transition Temperature in the M2AX family?

“…We then used this model on the full set of 13 M elements (with both A: Ge and Sn) and found that M=Cr was predicted to have the highest T c both times. Combining the insights from our previous studies [2,3] on the effect of changing A and X for fixed M, this suggested that Cr 2 AlN should be the best combination. To be robust we used this initial screening to identify the 5 best values of M (M: Ti, Cr, Fe, Nb and Mo) for further study in case the ranking changed as we varied A and X.…”

“…Nb 2 GeC has the highest experimental T c =10 K of any of these compounds currently known [30]. In a recent paper on Ti-based M 2 AX phases, we predicted Ti 2 AlN would have T c =13.0 K, which was the highest superconductivity temperature of all the materials studied [3].…”

“…The MAX phases are a fascinating family of materials, normally expressed as M n+1 AX n , n = 1, 2, 3, etc., where M is an early transition metal, A is an element from groups 12-16, and X is usually B, C or N [1][2][3]. They combine the metal-like properties of high electrical and thermal conductivity, machinability and mechanical strength [4][5][6][7][8][9][10][11] with the ceramic-like properties of good mechanical properties at high temperature and very good corrosion and oxidation resistance, high hardness, high creep lifetime [12][13][14][15][16][17][18][19].…”

“…We examined 9 new choices for A and found A=Al yielded the highest T c =6.7 K [2] of these. In our next study of Ti-based materials, we used the same approach to study 42 phases, of which only 3 were already known to be superconducting, and predicted that A=Al and X=N would have the highest T c =13.0 K [3].…”

“…Hence we first studied these four materials using detailed Eliashberg calculations and compared to known experimental T c values. We then extended this with detailed Eliashberg calculations to include additional phases M 2 AC (M: Nb, Ti, Mo and Lu; A: Ge and Sn), 3 of which we have already presented in previous works [2,3], and the 5 new sets of data are presented in the Supplementary Information. This was then used to generate a high-throughput screening model for M 2 AC (A: Ge and Sn).…”