Effects of domains

The first piezoceramic to be developed commercially was BaTi03, the model ferroelectric discussed earlier (see Section 2.7.3). By the 1950s the solid solution system Pb(Ti,Zr)03 (PZT), which also has the perovskite structure, was found to be ferroelectric and PZT compositions are now the most widely exploited of all piezoelectric ceramics. The following outline description of their properties and fabrication introduces important ideas for the following discussion of the tailoring of piezoceramics, including PZT, for specific applications. It is assumed that the reader has studied Sections 2.3 and 2.7.3. 

The current understanding is that the MPB is not a sharp boundary but rather a temperature-dependent compositional range over which there is a mixture of tetragonal and monoclinic phases. At room temperature (300 K) the two phases coexist over the range 0.455 x 0.48 [7]. The enhanced piezoelectric activity of 

As a ferroelectric perovskite in ceramic form cools through its Curie point it contracts isotropically since the orientations of its component crystals are random. However, the individual crystals will have a tendency to assume the anisotropic shapes required by the orientation of their crystal axes. This tendency will be counteracted by the isotropic contraction of the cavities they occupy. As a consequence a complex system of differently oriented domains that minimizes the elastic strain energy within the crystals will become established. 

The application of a sufficiently strong field will orient the 180° domains in the field direction, as nearly as the orientation of the crystal axes allows (see Section 2.7.3). The field will also have an orienting effect on 90° domains in tetragonal material and on 71° and 109° domains in the rhombohedral form, but the response will be limited by the strain situation within and between the crystals. There will be an overall change in the shape of the ceramic body with an expansion in the field direction and a contraction at right angles to it. When the field is removed the strain in some regions will cause the polar orientation to revert to its previous direction, but a substantial part of the reorientation will be permanent. 

An externally applied stress will affect the internal strain and the domain structures will respond this process is termed the ferroelastic effect. Compression will favour polar orientations perpendicular to the stress while tension will favour a parallel orientation. Thus the polarity conferred by a field through 90° domain changes can be reversed by a compressive stress in the field direction. Stress will not affect 180° domains except in so far as their behaviour may be coupled with other domain changes. 

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Akai P, To th NM (1983) Illite crystallinity Combined effects of domain size and lattice distortion. Acta Geol Hung 26 341-358... 

H. Maeda, M. Funahashi, J. Hanna, Effect of domain boundary on carrier transport of calamitic liquid crystalline photoconductive materials. Mol. Cryst. Liq. Cryst. 346, 183-192 (2000)... 

Manna, A. K., Pati, S. K. (2011). Tunable electronic and magnetic properties in BxNyCz nanohybrids effect of domain segregation. J. Phys. Chem. C 115(21), 10842-10850. 

Results of the loss tangent, tan 6, at low frequencies, obtained for a SEES copolymer and carbon nanotube (CNT)/polyurethane (PUR) nanocomposites, are analysed. The hindering effect of nanostructures (i.e. ordered domains or nanoparticles) on the motion of polymer chains is revealed by the occurrence of a mechanical relaxation at low frequencies. In the case of SEES copolymer, the effect of domains orientation and extender oil on a characteristic time associated with the relaxation is investigated. For CNT/PUR nanocomposites, the variation of the frequency at which the relaxation takes place, with CNT concentration and temperature, reveals that the interactions between the nanotubes and the polymer chains are improved with temperature... 

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