Scientists detect clue to material's unusual electrical properties

July 26, 2001

UPTON, NY -- Scientists at the U.S. Department of Energy's Brookhaven National Laboratory are studying a mysterious material that may lead to significant advances in the miniaturization of electronics. In the July 27, 2001 issue of Science magazine, the scientists describe findings that offer the first clues to explain the material's newly discovered, unusual electrical properties. This work may lead to applications using the material to store electrical charge in high-performance capacitors, and offer insight into how charges behave on the nanoscale -- on the order of billionths of a meter.

The material -- a perovskite-related oxide containing calcium (Ca), copper (Cu), titanium (Ti), and oxygen (O) in the formula CaCu3Ti4O12 -- is unusual in that it has an extremely high dielectric constant, a property that determines its ability to become electrically polarized (i.e., separate positive and negative electrical charges). The higher the dielectric constant, the more charge you can store, and the smaller you can make electronic circuits.

In addition, unlike most dielectric materials, this one retains its enormously high dielectric constant over a wide range of temperatures, from 100 to 600 Kelvins (K), or -173 to 327°C, making it ideal for a wide range of applications. Yet the material's dielectric constant drops precipitously -- 1,000-fold -- below 100K, with no evidence of structural or phase changes in the atoms. Therein lies the mystery.

"Such a large change in the way charge is distributed within the material implies that the atomic structure should change as well," said Christopher Homes, the lead physicist on the Brookhaven study. "It's difficult to imagine how one property can undergo such a large change while the other remains unaffected."

Previously, scientists have looked for hints of changes using x-rays, neutron beams, and other methods -- to no avail. But Homes' technique, measuring optical conductivity, or the material's ability to reflect and absorb varying frequencies of infrared light, revealed a number of unusual changes in the way the atomic structure vibrates.

The scientists detected the vibrations by illuminating samples of the substance with varying wavelengths of infrared light at Brookhaven's National Synchrotron Light Source, and measuring which wavelengths were reflected and which were absorbed. The absorbed wavelengths are those that match the atoms' natural vibration frequencies. As the temperature of the substance was cooled below the 100K mark, the absorbed frequencies -- and therefore the vibrations -- changed.

"Since the vibrations in a solid depend a great deal on how the charges are distributed, the changes in vibrations suggest that the charges can be rearranged without causing a structural distortion," Homes said. "The fact that we see these changes offers the first real glimpse of why this material has such a large dielectric constant, and the mechanism by which it decreases so dramatically below 100K."

The scientists speculate that at temperatures above 100K, pairings of positive and negative electric charges, called dipoles, can flip around quickly, independent of one another. This property and the high concentration, or density, of dipoles within the solid both contribute to the large dielectric constant. If you put the material in an electric field, all the individual dipoles flip into alignment to separate the charges.

But as the material cools, the dipoles "freeze out" in random positions, losing their ability to flip quickly into alignment. This "electronic phase transition" happens in the absence of a structural change. "Additional research will help us understand this effect and the range of ways this material might be used in microelectronics and other fields," Homes said.
This work was funded by the U.S. Department of Energy, which supports basic research in a variety of scientific fields.

The U.S. Department of Energy's Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies. Brookhaven also builds and operates major facilities available to university, industrial, and government scientists. The Laboratory is managed by Brookhaven Science Associates, a limited liability company founded by Stony Brook University and Battelle, a nonprofit applied science and technology organization.

Note to local editors: Christopher Homes lives in Saint James, New York.

DOE/Brookhaven National Laboratory

Related Lead Articles from Brightsurf:

Lead-free magnetic perovskites
Scientists at Linköping University, Sweden, working with the perovskite family of materials have taken a step forwards and developed an optoelectronic magnetic double perovskite.

Researchers devise new method to get the lead out
Researchers in the lab of Daniel Giammar, in McKelvey School of Engineering have devised a simple, quick and inexpensive way to quantify how much lead is trapped by a water filter.

Preventing lead poisoning at the source
Using a variety of public records, researchers from Case Western Reserve University examined every rental property in Cleveland from 2016-18 on factors related to the likelihood that the property could have lead-safety problems.

Silicones may lead to cell death
Silicone molecules from breast implants can initiate processes in human cells that lead to cell death.

Poor diet can lead to blindness
An extreme case of 'fussy' or 'picky' eating caused a young patient's blindness, according to a new case report published today [2 Sep 2019] in Annals of Internal Medicine.

What's more powerful, word-of-mouth or following someone else's lead?
Researchers from the University of Pittsburgh, UCLA and the University of Texas published new research in the INFORMS journal Marketing Science, that reveals the power of word-of-mouth in social learning, even when compared to the power of following the example of someone we trust or admire.

UTI discovery may lead to new treatments
Sufferers of recurring urinary tract infections (UTIs) could expect more effective treatments thanks to University of Queensland-led research.

Increasing frailty may lead to death
A new study published in Age and Ageing indicates that frail patients in any age group are more likely to die than those who are not frail.

Discovery could lead to munitions that go further, much faster
Researchers from the U.S. Army and top universities discovered a new way to get more energy out of energetic materials containing aluminum, common in battlefield systems, by igniting aluminum micron powders coated with graphene oxide.

Shorter sleep can lead to dehydration
Adults who sleep just six hours per night -- as opposed to eight -- may have a higher chance of being dehydrated, according to a study by Penn State.

Read More: Lead News and Lead Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to