Investigation of Piezoelectric Effect in Permanently Polarized Oxide Glasses and Glass-Ceramics.
Abstract : This research investigated the possible piezoelectric behavior of oxide glass samples subjected to phase separation and volume polarization. The concept consists of developing a glass composition which, when phase separated, produces a structure made up of isolated spheres within a low conductivity matrix. The conductivity of the spheres needs to be higher than the matrix at high temperatures but both materials must exhibit low conductivity at usage temperature. Thus, at high temperatures it is possible to apply an external electric field and polarize the isolated spheres by bulk ionic diffusion. When the sample is cooled to room temperature with the applied field and the applied field is removed when the sample is cold, a permanent polarization field will remain frozen in the spheres due to their low room temperature conductivity. Such material will exhibit intrinsic polarization and piezoelectic properties. Since the permanent polarization is developed throughout the glass, the piezoelectric behavior is not affected by surface polarization or by chemical reactions on the surface. Experiments are reported which demonstrate the use of phase separated glasses for development of permanently polarized electrets. Investigations of phase separation, dielectric relaxation and electrical conductivity of high silica glasses are presented.