Na2ZnH6: A 53K conventional superconductor near ambient pressure

Abstract

Ternary hydride Na₂ZnH₆ has been studied by employing density functional theory calculations. Our results find that Na₂ZnH₆ is dynamically stable but mechanically unstable at ambient pressure and exhibits strong electron-phonon coupling with $\lambda =2.42$. However, above 2.5 GPa pressure the crystal is mechanically as well as dynamically stable and exhibit strong electron-phonon coupling leading to significantly high T_c of ∼39K. The crystal is dynamically stable up to the isotropic pressure of 30 GPa. With increase in pressure, the electron-phonon coupling constant $\lambda$ and electronic density of states at Fermi level, N(E_F), decreases monotonously. But due to the anomalous trend in ${\omega }_{\log }$, the transition temperature, T_c, increases to a maximum of ∼53K at 5 GPa, followed by a drop to a minimum of ∼19K at 10 GPa. The T_c increases further till the pressure of 30 GPa and attains a maximum value of 58K. At 40 GPa and above, Na₂ZnH₆ becomes dynamically unstable and exhibits imaginary phonon frequencies. Our investigations offer an important input to experimentalists to investigate this new ternary hydride having reasonably high T_c near ambient pressure.