Aging of the Properties of Barium Titanate and Related Ferroelectric Ceramics

Abstract

Barium titanate ceramics show an aging effect during which the dielectric constant and electromechanical coupling factor decrease while the elastic constants and Q increase. At room temperature, this process takes over a year to stabilize. By heating the ceramic up to 70°C the process is considerably shortened. A comparison of the rates of aging at 70°C and 25°C shows that an activation energy of about 19 kilocalories per mole is involved the aging process. The experiments and calculations made show that the cause of the aging is a reduction in the effective polarization caused by a slow temperature-induced motion of the domain walls of the ceramic. This motion is biased by the residual strains stored up when the crystal becomes ferroelectric and also by strains induced by the poling process. It appears likely that the high activation energy measured arises from the simultaneous motion of a number of unit cells in a bordered wall. Due to this high activation energy, aging can be speeded up by a heat treatment process.