Ternary pentagonal BXN (X = C, Si, Ge, and Sn) sheets with high piezoelectricity.

The discovery of new and stable two-dimensional pentagonal materials with piezoelectric properties is essential for technological advancement. Inspired by recently reported piezoelectric materials -BCN and -BSiN, we proposed -BGeN and -BSnN as new members of the -family based on first-principles calculations. Comprehensive analyses indicated that both -BGeN and -BSnN are thermodynamically, dynamically, mechanically, and thermally stable. In terms of mechanical stability, the elastic constant decreased as lower elements in group 4A of the periodic table were used. Therefore, -BGeN and -BSnN are softer than -BCN and -BSiN. In terms of piezoelectric properties, piezoelectric stress and strain tensors increase following the same pattern. In group 4A, -BSnN had the highest intrinsic piezoelectricity, especially the piezoelectric stress. Typically, the piezoelectric strain coefficient increases with material softness; -BSnN possessed the highest . Thus, due to its inherent piezoelectricity, -BSnN has tremendous potential as a nanoscale piezoelectric material.