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 NaxSiy (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 (Tc) 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 Tc. 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.