The Curie Brothers Discover Piezoelectricity March 1880:physicsknow
Microphones, quartz watches, and inkjet printers all rely on an
unusual phenomenon known as the piezoelectric effect found in various
crystals, ceramics, and even bone. It was discovered by none other than
French physicist Pierre Curie, working with his older brother Jacq
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| Brothers and colleagues: Jacques (left) and Pierre (right) Curie, discoverers of the piezoelectric effect. |
ues,
who found that putting pressure on these materials created electricity
(the name comes from piezein — Greek for “squeeze”).
Born in Paris in 1859 to a physician named Eugene Curie, Pierre’s
early education was decidedly unorthodox: his father opted for private
tutors for his son, believing it to be the best approach given the boy’s
temperament and keen intellect. Pierre showed an early aptitude for
mathematics, and at 16 entered the Sorbonne for his university studies.
He successfully earned the equivalent of a master’s degree by 18, but
was forced to postpone his doctoral studies. During this time, he earned
a meager living as a lab instructor.
Pierre started conducting chemistry experiments at the age of 20 with
Jacques, focusing on the structure of crystals. They were especially
interested in the pyroelectric effect, in which a change in temperature
in a crystalline material generates an electric potential. This effect
had been known since the mid-18th century, thanks to the work of Carl
Linnaeus and Franz Aepinus, and subsequent scientists had hypothesized
that there could be a relationship between the properties of mechanical
stress and electrical potential. But experimental confirmation proved
elusive.
The brothers Curie thought there would be a direct correlation
between the potential generated by temperature changes and the
mechanical strain that gave rise to piezoelectricity. They expected that
a piezoelectric effect would arise in materials with certain crystal
asymmetries. Armed with the crudest of materials — tinfoil, glue, wire,
magnets, and a simple jeweler’s saw — they tested various types of
crystals, including quartz, topaz, cane sugar, Rochelle salt, and
tourmaline. As a result, the Curies found that when such materials were
compressed, the mechanical strain did indeed result in an electric
potential. The strongest piezeoelectric effects were found in quartz and
Rochelle salt. The brothers put their discovery immediately to good use
by inventing the piezoelectric quartz electrometer.
There was a twist to the piezoelectric saga still to come. The
following year, mathematician Gabriel Lippman demonstrated that there
should be a converse piezoelectric effect, whereby applying an electric
field to a crystal should cause that material to deform in response. The
brothers rushed to test Lippman’s theory, and their experiments showed
the mathematician was correct. Piezoelectricity could indeed work in the
other direction.
After the initial flurry of excitement died down, piezoelectric
research faded into the background for the next 30 years or so, in part
because the theory was so mathematically complex. But incremental
progress was still being made. In 1910, Woldemar Voigt published the
definitive treatise on the subject,
Lehrbuch der Kristallphysik,
a massive tome describing the 20-odd classes of natural crystal with
piezoelectric properties. More importantly, it rigorously defined the 18
possible macroscopic piezoelectric coefficients in crystal solids.
This set the stage for subsequent development of practical
applications for such materials, beginning with sonar in 1917, when Paul
Langevin developed an ultrasonic transducer for use on submarines using
thin quartz crystals. Many automobiles today have ultrasonic
transducers to assist drivers in measuring the distance between the rear
bumper and any obstacles in its path.
Pierre moved on to investigating magnetism, uncovering an intriguing
effect of temperature on paramagnetism now known as Curie’s law. Another
discovery was the Curie point: the critical temperature at which
ferromagnetic materials cease to be ferromagnetic. He even flirted with
paranormal spiritualism as the 19th century drew to a close, attending
séances with famed medium Eusapia Palladino, approaching them as a
scientific experiment with detailed observational notes, in hopes that
such study would shed light on magnetism. “I must admit that those
spiritual phenomena intensely interest me,” he wrote to his fiancée,
Marie Sklodowska, in 1894. “I think in them are questions that deal with
physics.”
Pierre married Marie the following year, when he also finally
completed his doctorate, thanks to her encouraging him to use his
magnetism work as a doctoral thesis. He became a professor of physics
and chemistry at Paris in 1895. (Jacques became a professor of
mineralogy at the University of Montpellier.) His new wife replaced his
brother as his scientific partner. The two discovered radium (and later,
polonium), sharing the 1903 Nobel Prize in Physics with Henri
Becquerel. The piezoelectric quartz electrometer invented by Pierre and
Jacques all those years before proved an essential instrument in their
ongoing work.
Towards the end of his life, Pierre showed early signs of
over-exposure to radium. In fact, his clothes were often so radioactive
he had to postpone experiments by several hours because it interfered
with his instruments. The unit of radioactivity is called the curie in
his and Marie’s honor. But he was spared a gruesome death by radiation
sickness. Instead, he was killed in a freak accident, run down by a
wagon on the Place Dauphine as he was crossing the busy street.
Marie always felt Pierre did not get the respect and support he
deserved from his scientific colleagues. He did not engage in academic
politics, preferring to focus on his research. He was rejected for a
professorship in mineralogy and denied membership in the French Academy
in 1903, the same year he won the Nobel Prize. His early work on
piezoelectricity was not, perhaps, his most significant discovery over
his illustrious career, but as he observed in an 1894 letter to Marie:
“[In science] we can aspire to accomplish something…. every discovery,
however small, is a permanent gain.”
