Influence of Substitutes and Dopants

The compositions of most dielectric materials used for ceramic capacitors are based on ferroelectric barium titanate. As discussed in detail in Pragraph 1.3 the permittivity of ferroelectric perovskites shows marked changes with temperature, particularly close to the phase transition. From the device point of view a high dielectric permittivity with stable properties over a wide temperature range is required. There are various specifications which have to be fulfilled (e.g. X7R AC/C(T = 25°C) 0.15 in a range between -55°C and 125°C). 

The dynamic of the cluster boundaries explains also the strong dielectric response under small ac fields. The naturally diffuse behavior (temperature stability) with high dielectric 

---