Ferroelectric perovskites

Oxygen Octahedra. An important group of ferroelectrics is that known as the perovskites. The perfect perovskite stmcture is a simple cubic one as shown in Figure 2, having the general formula ABO, where A is a monovalent or divalent metal such as Na, K, Rb, Ca, Sr, Ba, or Pb, and B is a tetra- or pentavalent cation such as Ti, Sn, Zr, Nb, Ta, or W. The first perovskite ferroelectric to be discovered was barium titanate [12047-27-7] and it is the most thoroughly investigated ferroelectric material (10). 

Figure 2.1 Schematic illustrations of intrinsic and extrinsic contributions to the piezoelectric constant of perovskite ferroelectrics. (a) and (b) correspond to the intrinsic unit cell shape (a) without and (b) with applied electric field, (c) and (d) correspond to the extrinsic response associated with the change in position of a non-180° domain wall (shown as a black line) (c) before and (d) after an electric field is applied. Note that both intrinsic and extrinsic responses lead to a change in shape of the material due to application of an electric field (and hence to a piezoelectric response). In both cases, the actual distortions are significantly exaggerated to make visualization easier.

Randall CA, Guo R, Bhalla AS, Cross LE (1991) Microstracture-properly relations in tungsten bronze lead barium niobate, Pbi tBa Nb206. J Mater Res 6 1720-1728 Reaney IM (1995) TEM observations of domains in ferroelectric and nonferroelectric perovskites. Ferroelectrics 172 115-125... 

Let us consider a spherical nanoparticle of radius R formed from perovskite ferroelectric. Polarization Ps(r) (r is a coordinate of a point inside the particle) and... 

We now consider the properties potential barrier of polarization reorientation for uniaxial and perovskite ferroelectric spherical nanoparticles. For uniaxial ferro-electrics the barrier between the states Po can be estimated on the basis of the free energy ... 

Subsequently we consider separately the cases of nanoparticles of the uniaxial and perovskite ferroelectrics with respect to the different forms of their free energy. 

For perovskite ferroelectrics with an a 2, the averaging over the angle cp in Fq, (4.78) leads to the expression ... 

As the polarization is not confined to a fixed direction in a monoclinic phase, its unconstrained rotation can explain the highly valued properties of ferroelectric systems near the MPB [25]. A relationship between the polarization rotation and a strong enhancement of the electromechanical response in perovskite ferroelectrics was demonstrated by Fu and Cohen [32], from a first principles study of the internal... 

Figure 18.23 Mechanically coupled magnetoelectric composites, (a) Crain mixture (b) Thin-film heterostructure (from Ref [123]) (c) Sandwich structure (from Ref [130]) (d) Spinel ferro/ ferrimagnetic nanopillars embedded on a perovskite ferroelectric matrix (from Ref [137].)...

The properties of transition-metal impurities, especially iron, in ABO perovskite ferroelectrics are of considerable interest due to their photochromic, photorefractive and other apphcations. 

Ferroelectrics belong to two general classes, those that imdergo order-disorder transition such as Rochelle salts, and those that imdergo displacive transitions such as the cubic perovskites. Ferroelectric behavior is restricted to 10 of the 32 point groups that are dipolar. The Curie temperature is also the transition temperature from a point group that permits ferroelectric behavior to one that does not. 

Bismuth layered perovskite ferroelectric materials were first found by Aurivillius in 1949 [ ] At that time, they were regarded as a kind of piezoeleetrie materials. However, since the appearance of Pb(Zr,Ti)03 (PZT), the bismuth layered perovskite ferroeleetric materials had... 

This chapter has been devoted to the piezoelectric performance of modem composites based on perovskite ferroelectric PbTiOs or its solid solutions. Modelling and effective-property predictions have been carried out for the matrix a-3 composites with stmctures shown in Figs. 1 and 7. It should be noted that elements of the hierarchical chain singledomain SC of PbTiOs - polydomain SC of PbTiOs - poled FC of modified PbTiOs are... 

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