Modifications of poled silicate glasses under heat treatment

Compositional and structural modification of the subanodic region of poled soda-lime glass under secondary heat treatment is studied using secondary ion mass spectrometry and micro-Raman techniques. A relaxation of the layered compositional distribution in the poled region of the glass remits to more equilibrium state in 250-780 degrees C temperature range, and the different relaxation mechanisms replace (and supplement) each other as the temperature rises. The main relaxation mechanism below the glass transition temperature, T-G, is alkalis hydrogen ions exchange, while at temperatures up to similar to 100 degrees C above T-G the main mechanism is the drift of alkali ions. At higher temperatures, up to 780 degrees C, the drift of calcium ions dominates. Heating the poled glass up to 780 degrees C results in partial crystallization of the subsurface layer of the poled glass with the formation of micron size grains, supposedly monoclinic dicalcium silicate, beta-Ca2SiO4.