Hydrogen (H-2)-induced optical switching properties of palladium-coated magnesium-nickel films were investigated. When the H content increased, the film started with an amorphous alpha-phase solution of H, and then became a mixture of amorphous alpha- and beta-phase, and finally an amorphous beta-phase solution of H. The film experienced volume changes, leading to damage of the Pd layer, followed by oxidation of the alloy layer and failure of the switching properties. If the Pd cover layer is made to have an appropriate thickness, the cyclic lifetime can be substantially extended to over 1000 cyclic exposures to 4% H-2 (in argon) and air. (C) 2010 Elsevier B.V. All rights reserved.