It must periodically dissolve to form mountains of dolomite, a common mineral. This seemingly paradoxical concept could help create new error-free semiconductors and more. For two centuries, scientists have failed to grow a common mineral in the laboratory under conditions believed to occur naturally. Now, a research team from the University of Michigan and Hokkaido University in Sapporo, Japan, has finally achieved this, thanks to a new theory developed from atomic simulations.

Their success solves an ancient geological mystery called the “dolomite problem.” Dolomite, an important mineral in the Dolomite Mountains in Italy, Niagara Falls, the White Rocks of Dover, and Hood in Utah, is very common in rocks more than 100 million years old, but is virtually absent in younger formations.

The importance of understanding dolomite growth

“If we understand how dolomite grows in nature, we can discover new strategies to promote crystal growth of advanced technological materials,” said Wenhao Sun, Dow Early Career Professor of Materials Science and Engineering at UCLA and corresponding author of the paper. published Science.

Finally, the secret to growing dolomite in the laboratory was to eliminate defects in the mineral’s structure as it grew. When minerals form in water, atoms usually settle neatly around the edges of the growing crystal surface. However, the growth boundary of dolomite consists of alternating calcium and magnesium rows. In water, calcium and magnesium adhere randomly to growing dolomite crystals, often getting trapped in the wrong place, creating defects that prevent additional dolomite layers from forming. This disorder gradually slows down the growth of dolomite, meaning that it would take 10 million years for just a single layer of ordered dolomite to be produced.

Fortunately, these defects are not recorded in the field. Because disordered atoms are less stable than atoms in the correct position, they are the first to dissolve when the mineral is washed with water. Repeated washing of these defects, for example by rain or tidal cycles, allows the dolomite layer to form in just a few years. Dolomite mountains can accumulate over geological time.

Advanced modeling methods

To accurately model dolomite growth, researchers needed to calculate how tightly or loosely atoms would bond to the existing dolomite surface. The most accurate simulation requires the energy of each individual interaction between electrons and atoms in the growing crystal. Such extensive calculations often require enormous computing power, but software developed at UM’s Center for Predictive Structural Materials Science (PRISMS) offered a shortcut.

“Our software calculates energies for some structures of atoms and then extrapolates to predict energies for other structures based on the symmetry of the crystal structure,” said Brian Puchala, one of the lead developers of the software and a UM research associate. Material science and engineering. This shortcut made it possible to model the growth of dolomite on geological time scales.

“On a supercomputer, each atomic step usually takes more than 5,000 CPU hours. We can now perform the same calculation in 2 milliseconds on a desktop computer,” said Junsu Kim, a doctoral student in materials science and engineering and first author of the study.

Practical application and verification of the theory

Today, some areas where dolomite occurs are periodically flooded and then dry out; This is in good agreement with Sun and Kim’s theory. But such evidence alone was not enough to be completely convincing. Yuki Kimura, a professor of materials science at Hokkaido University, and Tomoya Yamazaki, a postdoctoral researcher in Kimura’s laboratory, appear. They tested the new theory using transmission electron microscopes.

“Electron microscopes generally use only electron beams to image samples,” Kimura said. Said. “But the beam can also split water, creating an acid that can cause the crystals to dissolve. Normally this is bad for visualization, but in this case dissolution is exactly what we want.”

After placing a small crystal of dolomite in a solution of calcium and magnesium, Kimura and Yamazaki gently poked the electron beam 4,000 times over two hours, dissolving the defects. After the impacts, the dolomite was found to grow by about 100 nanometers (about 250,000 times less than an inch). Although there are only 300 layers of dolomite, no laboratory has ever grown more than five layers of dolomite before. Lessons learned from the dolomite problem could help engineers create better materials for semiconductors, solar panels, batteries and other technologies.

“In the past, crystal manufacturers who wanted to produce defect-free materials tried to grow them very slowly,” Sun said. “Our theory shows that if you periodically remove defects during growth, you can quickly grow defect-free materials.”