Electrochemically induced optical switching of Sm0.3Mg0.7Hx thin layers

The optical transmission of Sm0.3Mg0.7Hx thin films can be switched between transparent and absorbing by electrochemically altering the hydrogen content. In the colour neutral transparent, hydrogen rich (x = 2.3) composition the hydride has semiconducting properties. In the absorbing, hydrogen poor (x = 0.6) composition the hydride is a metal. The reflectivity is then 55%. The lateral resistance of the thin film was found to increase at the end of the hydrogen charging at high hydrogen content. This was in agreement with resistance measurements of the material when hydrogen charged in a gas ambient. In comparison with tungsten oxide films Sm0.3Mg0.7Hx thin films have a slightly lower coloration efficiency. A 200 nm thick layer can be switched over four orders of density in optical transmission. The maximum attainable change in transparency is large enough to enable the use as an optical shutter. The large change in hydrogen content upon charging and discharging the material compares favourably to LaNi5 and suggests use: as a hydrogen storage material. (C) 1998 Published by Elsevier Science B.V. All rights reserved.