Researchers from Japan's Shibaura Institute of Technology and National Institute for Materials Science have developed a method to grow single-crystal perovskite hydrides, enabling accurate hydride conductivity measurements.
Perovskite hydrides, whose molecular structure contains hydrogen anions (H−), attract special attention because of their hydrogen-derived properties and many believe they can be useful for hydrogen storage technologies such as fuel cells and next-generation batteries, as well as energy-saving superconducting cables. However, measuring their intrinsic hydride-ion conductivity is difficult. In their recent study, the researchers addressed this issue using a novel laser deposition technique in an H-radical atmosphere. Using this approach, they grew thin-film single crystals of two different perovskite hydrides and characterized their hydride-ion conductivity.
The scientists used an innovative approach to produce high-quality single crystals, and performed some of the first intrinsic conduction measurements on ternary perovskite hydrides.
To produce the perovskite single crystals, the researchers developed and pioneered a powerful method called 'H-radical reactive infrared laser deposition.' This approach involves shining an infrared laser onto a rotating disk-shaped pellet containing the metal atoms of the desired perovskite. In their study, the researchers wanted to produce MLiH3 (where M is either Sr or Ba), and thus the pellet was made of a crudely compressed mix of MH2 and LiH powders. As this pellet was heated up by the laser, the metals were released from it into a surrounding H-radical-rich atmosphere, obtained by injecting hydrogen into the reaction chamber through a heated tungsten filament.
Nearby the pellet was a carefully selected substrate, onto which the hydrogen and metals spontaneously combined to form the desired perovskite. As atoms began to pile up onto the substrate, they spontaneously arranged and aligned themselves in a consistent manner with the crystal layers below them. This led to the epitaxial growth of a nanofilm on the substrate.
The team explained that this approach is unique in its ability to perform deposition in a radical hydrogen atmosphere, significantly promoting the reaction between the metal and hydrogen. They further said that this results in the synthesis of single-phase hydride thin films by fully hydrogenating the metal atoms that naturally tend to persist in the film.
The researchers performed multiple laser depositions under a variety of conditions and thoroughly characterized the resulting thin films. Using many advanced techniques, including X-ray diffraction, atomic force microscopy, and scanning electron microscopy, they determined the elemental distribution and crystallinity of each of the films. In this way, they determined the optimum conditions in their experimental setup for growing well-ordered, single-crystal MLiH3.
After confirming the absence of grain boundaries in the films, the team could finally carry out H− conductivity measurements. These were the first measurements of the intrinsic H− conductivity of these crystals, a crucial information for selecting materials in many hydrogen-related applications.
This strategy for growing high-quality perovskite hydride crystals could open up new frontiers in hydrogen materials science and pave the way to sustainability.
