Lead zirconate titanate
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Lead zirconate titanate (Pb[ZrxTi1-x]O3 0<x<1) is a ceramic perovskite material that shows a marked piezoelectric effect. It is also known as lead zirconium titanate or PZT, an abbreviation of the chemical formula.
Being piezoelectric, it develops a voltage difference across two of its faces when compressed (used for sensor applications), or physically changes shape with an applied external electric field (used for actuators and the like).
It is also ferroelectric, which means it has a spontaneous polarization which can be reversed in the presence of an electric field.
The material features an extremely large dielectric constant at the morphotropic phase boundary (MPB) near x = 0.52. These properties make PZT-based compounds one of the most prominent and useful electroceramics. Commercially, it is usually not used in its pure form, rather it is doped with either acceptor dopants, which create oxygen (anion) vacancies, or donor dopants, which create metal (cation) vacancies and facilitate domain wall motion in the material. In general, acceptor doping creates hard PZT while donor doping creates soft PZT. In general, soft PZT has a higher piezoelectric constant, but larger losses in the material due to internal friction. In hard PZT, domain wall motion is pinned by the impurities thereby lowering the losses in the material, but at the expense of a reduced piezoelectric constant.
PZT is used to make ultrasound transducers and other sensors and actuators, as well as high-value ceramic capacitors and FRAM chips. PZT is also used in the manufacture of ceramic resonators for reference timing in electronic circuitry.
One of the commonly studied chemical composition is PbZr0.52Ti0.48O3. The increased piezoelectric response and poling efficiency near to x = 0.52 is due to the increased number of allowable domain states at the MPB. At this boundary, the 6 possible domain states from the tetragonal phase <100> and the 8 possible domain states from the rhombohedral phase <111> are equally favorable energetically, thereby allowing a maximum 14 possible domain states.
