An all-solid-state switchable mirror glass can change between its reflective (mirror) and transparent states by the use of an applied voltage. New energy-saving windows are expected to be one of the possible applications of the proposed device that utilizes this state change. In practical use, conventional windows are warmed by solar radiation of heat. Therefore, here we investigated the effects of temperature on the optical switching properties of the device. Although higher temperature increased the switching speed of the device, degradation occurred more rapidly. This result seemed to be related to the proton conductivity of the solid electrolyte layer of Ta(2)O(5). We confirmed the relationship between temperature and proton conductivity of the layer by the conventional impedance method. We found that higher temperatures resulted in higher proton conductivity of Ta(2)O(5), and at the interface of Pd and Mg(4)Ni thin films, hydride formation occurred. Hydride appeared to prevent the diffusion of protons into the optical switching layer, resulting ill imperfect switching. (C) 2009 Elsevier B.V. All rights reserved.