A subtle chemical interaction between metal and anion sublattices, not between atoms, in compounds is important when it comes to superhydrides – a new type of high-pressure compound with an extraordinarily high hydrogen composition and the ability to conduct electricity without loss of energy when formed is cooled below a critical value temperature.
Metal superhydrides, in particular, could help provide the answers scientists have been searching for ways to enable superconductivity without having to drop the temperature to extremely low levels, according to California State University chemistry professor Maosheng Miao, who added the researchers own the eight recipients of the prestigious 2022 Henry Dreyfus Teacher Fellow Award.
“The holy grail for many materials scientists is room-temperature superconductivity,” said Miao, who teaches at the CSUN College of Science and Mathematics. “The technology created by superconductivity is vital to so many aspects of our lives. For example, the MRT examinations (magnetic resonance imaging) that are so important in medicine are carried out by huge machines. Much of these machines are used to keep temperatures cool so that superconductivity can take place to create a strong magnetic field. Now imagine if you could do these scans with machines that don’t need to be kept at a specific temperature? This could revolutionize medicine and many other industries that rely on superconductivity.”
Miao said a new hope for this revolution could lie in metal superhydrides, chemical compounds that contain an unusually large amount of hydrogen.
“Ever since superconductivity was first discovered in 1911, people have been trying to find a way to achieve it at room temperature,” Miao said. “The recent discovery of superhydrides a few years ago brought us very close to room-temperature superconductivity, which could potentially transform energy transport and many other technologies. But efforts to improve superconductivity by raising the temperature and lowering the pressure on superhydrides are set back by the complexity of the structures and a lack of understanding of the chemical force driving the formation of these compounds.”
Determined to find the answers, Miao — a computational chemist who studies atoms and bonds and how they change under high pressure — proposed that metal lattices in superhydrides form templates that help form covalent hydrogen networks, and applied computer simulations based on the Use quantum mechanics to demonstrate this and quantize this subtle chemistry.
His results “Chemical templates that assembly metal superhydrides” were recently published in the journal Chem. The co-author of this two-author work is Yuanhui Sun, a research scientist in the CSUN Department of Chemistry.
“If you want to understand superhydrides,” he said, “you have to change your perspective. The chemistry between the individual atoms is not important, but rather the chemistry between the metal sublattice and the hydrogen sublattice. We first remove all the hydrogens from superhydrides and see the behavior of the electrons in what’s left.”
Miao and Sun showed that the electrons in the metal sublattice (“what’s left”) occupy the quantum orbitals, which are found in the large cavities between metal atoms. Since these local orbitals behave just like atomic orbitals, these cavities are called “quasi-atoms”. As they superimpose the hydrogen lattice over the electron state of the metal lattice, a harmonious relationship is created—they fit together perfectly, as if the electrons in the metal lattice form a template that anticipates and supports the construction of the hydrogen network.
A key point was that the template effect is not found in all metals, Miao said.
“This template, this driving force, explains beautifully why some metals can form superhydrides and other metals like aluminum cannot,” he said, adding that the theory goes beyond superhydrides.
“It’s a general chemical bonding theory,” Miao said. “This template effect exists in many compounds, including table salt. And because it’s so subtle, maybe that’s one of the reasons people haven’t looked into the role it plays in superhydrides.”
Miao said he hopes his findings will move the conversation forward as scientists continue their quest for room-temperature superconductivity.
“The theory greatly improves the efficiency of searching for new complex superhydrides by screening the metal templates,” he said. “Our work goes beyond superhydrides and transforms the empirical anion-in-metal approach into a true bonding theory that can greatly increase the efficiency of the search for new compounds and solve many mysteries of solid-state chemistry.”