Disorder Enables Extreme Sensitivity in Piezoelectric Materials

A research team working at the National Institute of Standards and Technology has found an explanation for the extreme sensitivity to mechanical pressure or voltage of a special class of solid materials called relaxors. The ability to control and tailor this sensitivity would allow industry to enhance a range of devices used in medical ultrasound imaging, loudspeakers, sonar and computer hard drives.

Relaxors are piezoelectrics—they change shape when a battery is connected across opposite ends of the material, or they produce a voltage when squeezed. “Relaxors are roughly 10 times more sensitive than any other known piezoelectric,” explains NIST researcher Peter Gehring. They are extremely useful for device applications because they can convert between electrical and mechanical forms of energy with little energy loss.

A team of scientists from Brookhaven National Laboratory, Stony Brook University, Johns Hopkins University and NIST used the neutron scattering facilities at the NIST Center for Neutron Research (NCNR) to study how the atomic “acoustic vibrations,” which are essentially sound waves, inside relaxors respond to an applied voltage. They found that an intrinsic disorder in the chemical structure of the relaxor crystal apparently is responsible for its special properties.

Atoms in solids are usually arranged in a perfect crystal lattice, and they vibrate about these positions and propagate energy in the form of sound waves. In typical piezoelectric materials, these acoustic vibrations persist for a long time much like the ripples in a pond of water long after a pebble has been thrown in.

Not so with relaxors: these vibrations quickly die out. The research team led by Brookhaven’s Guangyong Xu, compared how the sound waves propagated in different directions, and observed a large asymmetry in the response of the relaxor lattice when subjected to an applied voltage.

“We learned that the lattice’s intrinsic chemical disorder affects the basic behavior and organization of the materials,” says Gehring. The disorder that breaks up the acoustic vibrations makes the material structurally unstable and very sensitive to applied pressure or an applied voltage.

That disorder occurs because the well-defined lattice of atoms alternates randomly between one of three of its elements—zinc, niobium and titanium—each of which carries a different electrical charge.

The research was funded by the Office of Basic Energy Sciences within the U.S. Department of Energy’s Office of Science and the Natural Science and Research Council of Canada.

Citation: G. Xu, J. Wen, C. Stock and P.M. Gehring. Phase instability induced by polar nanoregions in a relaxor ferroelectric system. Nature Materials. Published online May 11, 2008.

Source: NIST

Related stories:

Surprising graphene: Honing in on graphene electronics with infrared synchrotron radiation
Graphene is the two-dimensional crystalline form of carbon: a single layer of carbon atoms arranged in hexagons, like a sheet of chicken wire with an atom at each nexus. As free-standing objects, such two-dimensional crystals were believed impossible to create -- even to exist -- until physicists at the University of Manchester actually made graphene in 2004.
A link between mitochondria and tumor formation in stem cells
Researchers report on a previously unknown relationship between stem cell potency and the metabolic rate of their mitochondria –a cell's energy makers. Stem cells with more active mitochondria also have a greater capacity to differentiate and are more likely to form tumors.
Promising new material that could improve gas mileage
With gasoline at high prices, it's disheartening to know that up to three-quarters of the potential energy you are paying for is wasted. A good deal of it goes right out the tailpipe instead of powering your car.
New knowledge about thermoelectric materials could give better energy efficiency
Thermoelectric materials can be assembled into units, which can transform the thermal difference to electrical energy or vice versa – electrical current to cooling. An effective utilization requires however that the material supplies a high voltage and has good electrical, but low thermal conductivity.
This is your grid on brains
(PhysOrg.com) -- Managing power networks in the future may involve a little more brain power than it does today, if researchers at Missouri University of Science and Technology succeed in a new project that involves literally tapping brain cells grown on networks of electrodes.
Models of Eel Cells Suggest Electrifying Possibilities
(PhysOrg.com) -- Engineers long have known that great ideas can be lifted from Mother Nature, but a new paper by researchers at Yale University and the National Institute of Standards and Technology takes it to a cellular level. Applying modern engineering design tools to one of the basic units of life, they argue that artificial cells could be built that not only replicate the electrical behavior of electric eel cells but in fact improve on them. Artificial versions of the eel’s electricity generating cells could be developed as a power source for medical implants and other tiny devices, they say.
The hybrid offensive
(PhysOrg.com) -- Fraunhofer research engineers are busy converting a standard production gasoline-engine car into a hybrid. By doing so, they aim to demonstrate what hybrid technology can do, and prove that it can even be integrated in existing vehicle design concepts.
When a light goes on during thought processes
(PhysOrg.com) -- Thought processes made visible: An international team of scientists headed by Mazahir Hasan of the Max Planck Institute for Medical Research in Heidelberg has succeeded in optically detecting individual action potentials in the brains of living animals. The scientists introduced fluorescent indicator proteins into the brain cells of mice via viral gene vectors: the illumination of the fluorescent proteins indicates both when and which neurons are communicating with each other.

News discussion:

Physics news