Some factors affecting the dielectric and piezoelectric properties of barium titanate ceramics

In the preparation of barium titanate ceramics for dielectric and piezoelectric applications careful attention must be given to a great many factors which determine the ultimate performance of the ceramic. Attention is drawn to structural differences observed with the aid of electron micrographs as the time and temperature of firing are varied. At lower temperatures and shorter firing intervals crystals remain small, grain boundary areas are relatively large and numerous voids are observed where several crystals join. As the time and/or temperature are increased crystals become larger with an improved grain boundary condition resulting in better structure. An optimum condition is soon reached beyond which rounding of edges at grain boundaries where several crystals join is more pronounced. This causes an increase in the number of voids. Accompanying these changes the 1 kc dielectric constant, the piezoelectric constants (thickness mode), and coupling coefficients first improve, reach optimum values and then decline slightly, but the resistance to depoling continually decreases. The resistance to depoling is related to the long term stability of the remanent Polorization.