A Greek scientist, Theophrastus, first noticed the pyroelectric effect in
340 B.C. in experiments with tourmaline, a crystal silicate containing
various metallic elements. In 1707, Johann Georg Schmidt showed that by
heating or cooling tourmaline (as well as several other classes of crystals of proper geometries), a positive or negative electric field could be
induced in the crystal.
In 1880, scientist-brothers Jacques and Pierre Curie discovered that they
could also induce an electric field in certain classes of crystals, not by
heating or cooling them, but by applying a mechanical stress. In addition,
they realized that by changing the direction of the mechanical stress (i.e.,
a compression or expansion) they could control the sign of the electric
field created. Their prior knowledge of pyroelectricity led them to this
discovery, and they dubbed the phenomenon the piezoelectric effect,
from the Greek piezein, meaning “to push.” Today this is known as the
direct piezoelectric effect—the ability of a crystal to produce an electric field
in response to mechanical stress.
In subsequent years, the Curie brothers and other scientists began mapping out the crystalline structure requirements for piezoelectricity. They
found that crystals possessing piezoelectric qualities have neither an
absolute center nor a plane or axis of symmetry perpendicular to the axis
of electric activity (the plane on which the electric field arises). There are
currently 21 known classes of crystals that exhibit the piezoelectric effect.
Three representative materials with crystal structures that exhibit piezoelectricity are quartz, cane sugar, and bone.
Another important advance in the understanding of piezoelectricity
came with the discovery that a piezoelectric crystal would be physically
deformed (e.g., expand or contract) in response to an applied voltage.
This effect was effectively the opposite of the direct piezoelectric effect and
was subsequently named the converse piezoelectric effect. It was also discovered that the converse piezoelectric effect could be used to induce
vibrations along a crystal. By applying a precise alternating current, the
deformations of the crystal could be rapidly changed between expansion
and contraction, causing the crystal to oscillate.
The piezoelectric effect is the foundation of a host of technologies. One of
the original applications was a piezoelectric device used during the
development of sonar in which piezoelectric quartz crystals were used as
transducers to detect echoes returning from underwater objects. Piezoelectric devices are also commonly used in microphones—the air pressure fluctuations caused by a sound distort the piezoelectric device in the
CHAPTER 8: Surface Characterization and Imaging Methods
260
340 B.C. in experiments with tourmaline, a crystal silicate containing
various metallic elements. In 1707, Johann Georg Schmidt showed that by
heating or cooling tourmaline (as well as several other classes of crystals of proper geometries), a positive or negative electric field could be
induced in the crystal.
In 1880, scientist-brothers Jacques and Pierre Curie discovered that they
could also induce an electric field in certain classes of crystals, not by
heating or cooling them, but by applying a mechanical stress. In addition,
they realized that by changing the direction of the mechanical stress (i.e.,
a compression or expansion) they could control the sign of the electric
field created. Their prior knowledge of pyroelectricity led them to this
discovery, and they dubbed the phenomenon the piezoelectric effect,
from the Greek piezein, meaning “to push.” Today this is known as the
direct piezoelectric effect—the ability of a crystal to produce an electric field
in response to mechanical stress.
In subsequent years, the Curie brothers and other scientists began mapping out the crystalline structure requirements for piezoelectricity. They
found that crystals possessing piezoelectric qualities have neither an
absolute center nor a plane or axis of symmetry perpendicular to the axis
of electric activity (the plane on which the electric field arises). There are
currently 21 known classes of crystals that exhibit the piezoelectric effect.
Three representative materials with crystal structures that exhibit piezoelectricity are quartz, cane sugar, and bone.
Another important advance in the understanding of piezoelectricity
came with the discovery that a piezoelectric crystal would be physically
deformed (e.g., expand or contract) in response to an applied voltage.
This effect was effectively the opposite of the direct piezoelectric effect and
was subsequently named the converse piezoelectric effect. It was also discovered that the converse piezoelectric effect could be used to induce
vibrations along a crystal. By applying a precise alternating current, the
deformations of the crystal could be rapidly changed between expansion
and contraction, causing the crystal to oscillate.
The piezoelectric effect is the foundation of a host of technologies. One of
the original applications was a piezoelectric device used during the
development of sonar in which piezoelectric quartz crystals were used as
transducers to detect echoes returning from underwater objects. Piezoelectric devices are also commonly used in microphones—the air pressure fluctuations caused by a sound distort the piezoelectric device in the
CHAPTER 8: Surface Characterization and Imaging Methods
260