Electron-beam damage in cathodochromic sodalite

In recent years sodalite, Na8Al6Si6O24X2, where X is Cl, Br, or I, has received wide attention as a cathodochromic material. The utility of sodalite, however, is severely restricted because of damage produced after repeat write-erase cycles. This damage was investigated and found to be of two kinds. The first kind was considerable loss of potential color centers, i.e., after a certain number of write-erase cycles the material would not color up to the original optical density. The second kind was build up of permanent coloration which could not be removed on exposure to bleaching light but could be removed by heat. Electron microprobe, electron spectroscopy for chemical analysis, thermogravimetric analysis, x rays, and a variety of other analytical tools were used to understand the causes of damage. Considerable loss of sodium and a smaller loss of halogen ions on continued electron-beam irradiation was found to be closely associated with the damage. Possibility of heat generated by the electron beam was discounted as the source of damage.