Pyroelectrics, ferroelectric/piezoelectric perovskites

A wide array of ferroelectric, piezoelectric and pyroelectric materials have titanium, zirconium and zinc metal cations as part of their elemental composition Many electrical materials based on titanium oxide (titanates) and zirconium oxide (zirconates) are known to have structures based on perovskite-type oxide lattices Barium titanate, BaTiOs and a diverse compositional range of PZT materials (lead zirconate titanates, Pb Zr Tij-yOs) and PLZT materials (lead lanthanum zirconate titanates, PbxLai-xZryTii-yOs) are among these perovskite-type electrical materials. 

Table 27.5 lists applications of some of the most commercially important mixed metal, perovskite-t5q)e oxides, and illustrates that it is the dielectric, ferroelectric, piezoelectric (see Section 13.9) and pyroelectric properties of these materials that are exploited in the electronics industry. 

Until the late sixties the only known ferroelectrics, piezoelectrics, and pyroelectrics were certain inorganic monocrystals, or polycrystalline ceramics like lead titanate zirconate perovskites. Other known materials with macroscopic polarization were electrets, (for example mixmres of beeswax and rosin) in which the polarization was produced by application of the electric field in the melted state and then by cooling and the solidification of the polarized material. 

In this chapter, the emphasis is upon dielectric and ferroelectric perovskites. As ferroelectrics are also piezoelectrics and pyroelectrics, it is found that most important applications for both piezoelectric and pyroelectric perovskites make use of ferroelectric materials. 

Piezoelectricity and ferroelectricity are the result of electric dipole effects that are due to ions shifting from their initial positions in the lattice. This effect, which is strongly structure-dependent, was discussed above. Pyroelectric materials have permanent electric dipole moments, their magnitude varying with temperature. In infrared detectors, use is made of the ferroelectric phase transitions in perovskites. 

Relatively few applications have utilized the ferroelectric effect in ceramics. Ferroelectric ceramics have been widely employed because of the other properties that they display, however. Their dielectric, piezoelectric, and pyroelectric properties have led to their use in capacitor, actuator and other piezoelectric applications, and infrared detection devices. Again, the most widely used materials are the lead-based ABO perovskite compounds. 

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