In the realm of energy and materials science, a team of researchers from the University of California, Davis, and the University at Buffalo, The State University of New York, has been delving into the behavior of ammonium polyhydrides under extreme conditions. Kyla de Villa, Xiaoyu Wang, Eva Zurek, and Burkkhard Militzer have recently published their findings in the journal Nature Communications, shedding light on the intriguing phenomenon of superionicity in these compounds.
Ammonium polyhydrides are compounds that combine nitrogen and hydrogen in various ratios. The researchers studied several of these compounds, with varying amounts of hydrogen, under high pressures ranging from 100 to 300 gigapascals (GPa). These pressures are far beyond what we encounter in everyday life but are thought to exist in the interiors of giant planets. The team used advanced computer simulations to explore how these compounds behave when heated, observing transitions between solid, superionic, and liquid phases.
The researchers found that as the temperature increases, the ammonium polyhydrides exhibit a phase known as superionicity. In this phase, the hydrogen atoms become highly mobile, diffusing rapidly through the material while the nitrogen atoms remain relatively fixed. This behavior is akin to an ionic liquid, where ions are free to move, but in this case, it’s the hydrogen atoms that are on the move.
The team identified several key indicators of these phase transitions. These include changes in the internal energy and pressure of the material, the formation of new chemical species, and significant increases in atomic diffusion rates. Notably, they observed that as the proportion of hydrogen in the compound increases, the temperatures at which these transitions occur decrease. This trend suggests that compounds with a high enough hydrogen content may skip the superionic phase altogether and melt directly from the solid phase.
The practical implications of this research for the energy sector are still emerging, but understanding the behavior of materials under extreme conditions can inform the development of new energy technologies. For instance, the insights gained from studying superionic phases could potentially contribute to the design of advanced energy storage systems or inform our understanding of planetary interiors, which in turn could aid in the exploration of energy resources on other planets. Moreover, the methods developed to detect and analyze these phase transitions could be applied to other materials research, broadening the scope of potential applications.
This article is based on research available at arXiv.