Researchers Resolve 40-Year Dispute Over Disappearing Physical Property

(PhysOrg.com) -- A property that can be used for memory in electronic devices disappears at high temperatures, and University of Arkansas scientists and colleagues in the Czech Academy of Sciences have used both theory and experiment to resolve a 40-year-old dispute over how this property disappears.

Research professor Inna Ponomareva and physics professor Laurent Bellaiche, both of the J. William Fulbright College of Arts and Sciences; Jirka Hlinka, a visiting professor from the Institute of Physics at the Czech Academy of Sciences, and their colleagues reported their findings in a recent issue of Physical Review Letters.

The property in question is ferroelectricity, which is found in substances that have a spontaneous polarization that can be switched by applying an electric field. These materials are used in electronic devices, but cannot be used at high temperatures, because the ferroelectric property disappears.

The researchers set out to determine why the material loses polarity – is it because the dipole moment, measured by the charge and distance between atoms, disappears completely, or is it because dipole moments become fully disordered and cancel one another? They looked at a classic ferroelectric material, barium titanate, using supercomputers to create new computational simulations and time-domain terahertz spectroscopy techniques – both cutting-edge methods for examining the issue.

“We got very good agreement between the theoretical and experimental work,” Ponomareva said.

The two scenarios depend upon the collective motion of the titanium ions, restricted by surrounding oxygen ions. Both theoretical and experimental observations show that, occasionally, whole rows of the titanium atoms make unusually large simultaneous shifts. This collective “jumping” had not been seen experimentally before.

The movement of titanium atoms helps explain the ferroelectric properties that exist in such materials, as well as why these properties disappear at high temperatures.

“These excitations had not been seen experimentally before,” said Hlinka. “Now we have a better understanding of the way this compound works.”

Bellaiche holds the Twenty-First Century Endowed Professorship in Nanotechnology and Science Education.

Citation: Coexistence of the Phonon and Relaxation Soft Modes in the Terahertz Dielectric Response of Tetragonal BaTiO3, Phys. Rev. Lett. 101, 167402 (2008)
http://link.aps.org/abstract/PRL/v101/e167402

Provided by University of Arkansas

   

• barakn - Oct 21, 2008
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  Is it just me or did they not clearly state whether it is because the dipole moment disappears completely, or whether it is because dipole moments become fully disordered and cancel one another?
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• legendmoth - Oct 21, 2008
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  "experimental observations show that, occasionally, whole rows of the titanium atoms make unusually large simultaneous shifts. This collective %u201Cjumping%u201D had not been seen experimentally before."
  Doesn't an experimental observation mean that it has been seen experimentally? Have they or have they not observed this before?
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• tkjtkj - Oct 22, 2008
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  I urge others to read this
  article as an example of
  "obfuscating techno-writing".
  
  "Jumping" ?? just HOW does
  jumping relate to conductivity
  in this circumstance??
  
  I walk away from such articles
  feeling empty ...
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• lomed - Oct 23, 2008
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  The article in Physical Review Letters seems to indicate that they were looking for a result related to the order-disorder parameter of the crystal. It also says that both modes were found with differing contributions to various properties of the material such as reflectivity and dielectric response (which sounds like it might have something to do with conductivity.) Specifically, the order-disorder mode was shown to contribute to the dielectric response (among other things) which, I believe, was the (experimentally but not theoretically) new result about which the article is talking.
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