Controllable optical transitions of amorphous Mg and Mg–Ni films via electrochemical methods

Abstract

Amorphous Mg and MgNix (0.03 ≤ x ≤ 0.30) thin films capped with Pd were prepared by magnetron co-sputtering, and their hydrogen-induced optical transitions were investigated via electrochemical charging and discharging in KOH electrolyte solution. Repetitive transitions, up to dozens of times between the mirror state and transparent state, are achieved in these amorphous Mg and MgNix thin films even though some performance degeneration occurs during cycling. These deteriorations are mainly attributed to the breakdown of the film structure, which is caused by both a large change in film volume during cycling and the corrosive attack of the KOH electrolyte. In addition, calculations based on the electrochemical stripping method indicate that the hydrogen diffusion coefficient is significantly increased by amorphization; however, it is only slightly improved by the addition of Ni. Among the prepared amorphous films, MgNi0.09 film shows the largest hydrogen diffusion coefficient, namely, 2.64 × 10(-13) cm(2) s(-1). More importantly, the optical properties of the amorphous Mg and MgNix films are readily manipulated in the charging process, especially under a small charging current density, where there is a linear correlation between charging capacity and transmittance. The tunable optical properties obtained in the present study will greatly expand the application fields of Mg-based thin films.

Nanostructural Perspective for Destabilization of Mg Hydride Using the Immiscible Transition Metal Mn

“…Theoretical calculations have indicated that MgH 2 thin layers with a thickness below 10 unit cells and MgH 2 particles with a grain size smaller than 1.3 nm would reduce the stability of MgH 2 . Alterations in hydrogen absorption/desorption properties were reported in Mg and its alloy thin films prepared by means of magnetron sputtering. − It has been shown that in addition to nanosizing, the utilization of immiscible metals with Mg can modify the thermodynamics more effectively. − A multilayer stack of Mg/Ti with a typical layer thickness below 10 nm revealed a large destabilization of MgH 2 due to the extra contribution of the interface energy difference Δγ between Mg/TiH 2 and MgH 2 /TiH 2 . For Ti-rich Mg–Ti alloy thin films and powders, nanometer-sized MgH 2 clusters coherently embedded in a TiH 2 matrix are formed upon hydrogenation, again resulting in enhanced destabilization of MgH 2 by the interface energy. , Recently, we succeeded in obtaining an even more destabilized MgH 2 by the addition of Cr to the Mg–Ti system: Cr is also immiscible with Mg and expected to increase the interface energy effect …”