Discovery and Prediction on a Family of Hard Superconductors with Kagome Lattice: XY3 Compounds

The search for and design of superconductors with both Kagome lattice and hardness is a challenging and frontier research topic. This work utilizes structure predictions to discover the Kagome lattice in NaSi₃_P6/mmm phase of Na_xSi_y (x, y = 1–3). For a comprehensive understanding of XY₃_P6/mmm, other atoms such as X = Li, Na, Cs and Y = B, Si, Ge are included. Superconducting critical temperatures (T_c) of XY₃ compounds are calculated between 0 and 20 GPa and found to be 30.54 K for CsB₃ at 0 GPa, indicating that electron–phonon coupling, phonon softening, linewidths, and electron density at the Fermi level all have significant effects on T_c. The bonding type of B, Si, and Ge atoms in the Kagome lattice also determines the boundaries of its hard properties and superconductivity. Moreover, the melting temperature of NaSi₃_P6/mmm is determined to be 608 K at 0 GPa and P–T phase diagram at pressures of 0–15 GPa using deep learning molecular dynamics simulations. Our findings provide a multitude of excellent properties in the XY₃ compounds, including Kagome lattice, high hardness, and superconductors, which will provide essential physical insights and theoretical guidance for the experimental exploration of the hard superconductors.