Tunable reflectance Mg–Ni–H films

Mg 2 NiH x switchable mirrors, which switch from shiny metallic Mg2Ni to transparent Mg2NiH4, are shown to exhibit also dramatic reversible changes in reflectance at remarkably low hydrogen concentrations. Already for x≅0.3 a 232 nm thick Mg2NiHx film has an absorptance of ∼90% over the whole visible optical spectrum. The transition from highly reflective to black occurs in the concentration interval 0.1<x<0.3. The volume changes involved are one order of magnitude smaller than in the transition from reflecting to transparent. This is expected to enhance the lifetime of future devices based on these materials.