Crystal Clear

Caitlin Elizabeth Rockett

On July 24, Tara Michels-Clark arrived in Zurich, Switzerland to autumn-like temperatures and gray skies. The third-year doctoral student in the department of chemistry at the University of Tennessee, Knoxville (UT) was arriving in Switzerland’s largest city to begin a month-long interdisciplinary, international project aimed at developing software to model and visualize disordered crystal structures.

Tara is a member of Robert Harrison’s chemistry lab at UT. Harrison also serves as the director for the Joint Institute for Computational Sciences, a cooperative project between UT and Oak Ridge National Laboratory (ORNL) that seeks to advance scientific discovery and education in computational science. Harrison has functioned as Tara’s graduate advisor for the past two years as she’s expanded her studies in crystallography.

“In general, knowing the structure of a material can often help reveal the reason for the functional properties it has,” Tara explained about the benefit of modeling crystalline structures.

Crystals are solid materials whose atoms, molecules, or ions are arranged in a methodical, repeating pattern. However, there are exceptions to most rules and many crystals lack perfectly defined structural order. It’s this disorder that gives some crystals novel uses.

“Take sodium lanthanum tetrafluoride for example,” offered Tara. “It’s an up-conversion compound—its disorder gives it an optical component. Appropriately doped sodium lanthanum chloride converts red light to green light and is used in LED displays.” In this case, ‘doped’ refers to introducing another substance that enhances a useful function of the original compound.

“That’s just one example,” she explained. “Being able to model diffuse scattering in general will be something that is very useful in materials research.”

Diffuse scattering begins with a beam of x-rays directed at a crystal with an undetermined atomic structure. When the light hits the atoms it spreads in different directions. After measuring the angles and intensities of these diffracted rays, scientists can begin to piece together a picture of the crystal, from the position of the atoms to their chemical bonds, as well as the disorder of the atoms.

Crystalline structures comprise a multitude of everyday commodities, from table salt to diamonds. Understanding not only their composition but also their structure helps researchers understand how we can best use these natural resources.

Take graphite and diamonds as a simplified example—both are commonplace crystalline structures and both are made of carbon—but a look at their atomic structure explains why these two solids function so differently. While the soft graphite found in pencils is made of loosely bonded sheets of carbon, diamonds get their strength from tightly stacked carbon bonds.

The crystal-modeling project in Switzerland is a collaboration between ORNL, the University of Zurich, the Federal Institute of Technology, and the University of Bern. The group’s work is funded through the Sinergia project of the Swiss National Science Foundation. Sinergia provides a means for collaboration between three to six research groups tackling a promising area of research, even if the collaboration crosses nations.

As a student with the project, Tara worked on testing the software the team is creating—a code called ZODS, or the Zurich/Oak Ridge Disorder Simulation. The code allows scientists to visualize crystals on an atomic scale where the properties of the compound originate.

According to Tara, the opportunity to work in Switzerland came about in a rather roundabout way. As a student at UT, which partners with Battelle to manage ORNL, Tara already had ties to ORNL. As such, she was able to participate in the project’s kickoff meeting before she even began her graduate studies in 2009. That same year she was also able to attend the annual Zurich School of Crystallography, which happened to be managed by people associated with the ZODS project. When the researchers at ZODS decided they wanted to give a student a chance to travel abroad and study, Tara was a strong fit.

Once in Switzerland, Tara got the chance to enjoy a little cultural education in addition to the academic kind, and she took the time to blog about it all.

Her blog describes Swiss National Day, which is a bit like Independence Day in the United States, replete with fireworks, a day off work, and lots of food and drink. She also got the chance to witness the world-renowned Zurich Street Parade on its 20th anniversary. With dozens of trucks carrying sound equipment, DJs, and wildly dressed dancers, the Street Parade is a walking discotheque that promotes not only fun, but also tolerance and respect.

While it’s clear from the pictures and posts in her blog that Tara was enjoying the company of such gifted collaborators and the exciting culture of Switzerland, this was the longest she had ever been away from her family—her husband and three rabbits.

“That’s the hard part,” Tara admitted easily, adding with a laugh, “I use Skype with my husband about every night, and he puts the bunnies on so I can say ‘hi.’”

As her four weeks in Switzerland drew to a close toward the end of August, Tara got to spend a quick weekend with her sister in London before heading to Madrid, Spain where she had been invited to present results from the ZODS project at the International Union of Crystallography conference. After the conference, Tara headed back to Knoxville to resume her graduate classes.

As a third year student, Tara still has a lot of school and research ahead of her, but she hopes to build a career as a scientific staff member at a national lab or in theoretical crystallography at a synchrotron or neutron facility.

Visit Tara’s blog to read more about her research and experience in Switzerland.