Switchable mirrors are thin films of metals or alloys which show a reversible transition from a reflecting metallic state
to a transparent semiconducting state upon hydrogen exposure. We investigated the parameters which influence the
kinetics of thin films of magnesium nickel alloys capped with a thin catalytic palladium layer. We found that the
kinetics are strongly dependent on the composition of the films which is demonstrated by measurement of the
transmittance and the reflectance of the substrate and the film sides during switching. In the case of the hydrogenation
reaction this is because of the different hydride nucleation behavior of the layers. It is shown that this behavior is
controlled by interface reactions during the deposition of the layers and by structural features. Nucleation at the
substrate interface is believed to be due to heterogeneous nucleation of magnesium nickel hydride on MgO particles.
This reaction is suppressed by alloying of magnesium and palladium at the magnesium palladium interface. Nucleation
in the layer volume seems to be inhibited in the case of non crystalline magnesium nickel layers. All these features lead
to fast hydrogenation kinetics and good optical properties in the hydride state for intermediate layer compositions.