Pressure-induced formation of cubic lutetium hydrides derived from trigonal LuH3

In recent years, there has been a fervent search for room-temperature superconductivity within the binary hydrides. However, as the number of untested compounds dwindled, it became natural to begin searching within the ternary hydrides. This led to the controversial discovery of room-temperature superconductivity at only 1 GPa in nitrogen-doped lutetium hydride [Dasenbrock-Gammon et al., Nature (London) 615, 244 (2023)] and consequently provided much impetus for the synthesis of nitrogen-based ternary hydrides. Here, we report the synthesis of stable trigonal LuH3 by hydrogenating pure lutetium which was subsequently pressurized to similar to 2 GPa in a dilute-N2/He-rich pressure medium. Raman spectroscopy and x-ray diffraction were used to characterize the structures throughout. After depressurizing, energy-dispersive and wavelength-dispersive x-ray spectroscopies characterized the final compound. Though our compound under pressure exhibits similar structural behavior to the Dasenbrock-Gammon et al. sample, we do not observe any nitrogen within the structure of the recovered sample at ambient pressure. We observe two cubic structures under pressure that simultaneously explain the x-ray diffraction and Raman spectra observed: The first corresponds well to Fm3m LuH2+x, while the latter is an Ia3-type structure.