A remarkable find was incurred by
Pierre and Jacques Curie in the 1880's. They had noticed that
1. Applying pressure or mechanical
stress on certain natural nonsymmetrical crystals produced an electrical
charge in direct proportion to the pressure
2. They also found that when those same
crystals where subjected to an electric field, they expanded or
contracted in direct proportion to that electrical field.
These collective properties are today
go by the symantec "Piezoelectric effect". As one may imagine,
components exhibiting these controlled mechanical and/or electrical properties could be very useful in a wide
variety of goods and/or devices. They (Piezos) can serve as
durable electromechanical transducers converting mechanical energy into
electrical and similarly converting electrical energy into mechanical.
Diagrams/Overview of the
Piezoelectric Phenomenon
| Above
the Curie Temperature, the crystal structure is cubic and has no
electric dipole movement. |
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| However, below this temperature the positively charged Ti/Zr ion
shifts from its central location along one of several allowed
directions. This slightly distorts the crystal lattice into
a perovskite structure (a tetragonal/rhombohedra shape), and
produces an electric dipole with a single axis of symmetry. |
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| Immediately after sintering, groups of molecular diploes align
within small areas, or domains, to form large dipole moments.
PZT is made up of many such domains; however, as they are randomly
oriented, their net electric dipole is zero. |
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| If PZT
is subjected to a large electric field at elevated temperatures,
the domain diploes align in the allowed direction most closely in
line with the field. This process is called Polarization and
causes the PZT to exhibit the Piezoelectric Phenomenon. The
diploes will maintain this orientation even after the dc field is
removed (remnant polarization), a necessary condition for the
Piezoelectric behavior of ferroelectric ceramics. |
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