Physics of ferroelectric ceramics used in electronic devices

Abstract

During the last few years ferroelectric ceramics have attained increasing importance as materials for electronic devices. Present world production of such devices is more than 1010 per year. Since the suitability of these materials is due to their ferroelectric nature, this paper will mainly discuss the correlation of their physical ferroelectric behaviour and their many applications.As compared to single crystalline materials, polycrystalline ceramics are preferred firstly because of their lower cost and secondly because of the possibility of preparing doped mixed crystals of almost any composition with optimum properties. On the other hand certain disadvantages are present in ceramics: the physical effects in single crystals can only partially be exploited in ceramics. Furthermore ceramics suffer from characteristic instabilities.The materials discussed here are all oxides based on BaTiO3 and Pb(Ti, Zr)O3 with perovskite structure. The large variation of their physical properties, which is very convenient for applications, is brought about by modifying the two base materials by mixed-crystal formation with other oxide perovskites, together with additional doping. According to the type of application ferroelectric ceramics can be classified in three groups: piezoelectric, dielectric and PTC materials which will be discussed in detail.