Synthesis, Structural, and Raman Investigation of Lanthanide Nitride Powders (Ln = La, Ce, Nd, Sm, Gd, Tb, Dy, Er, Lu)

Abstract

Lanthanide nitride (LnN) materials have garnered significant interest in recent years due to their promising potential as heterogeneous catalysts for green ammonia synthesis under low temperature and pressure reaction conditions. Here, we report on the synthesis of an extended series of lanthanide (Ln) nitride powders (Ln = lanthanum, cerium, neodymium, samarium, gadolinium, terbium, dysprosium, erbium, lutetium) and their structural and vibrational properties. Polycrystalline powders were fabricated using a ball milling mechanochemical process, and their structural properties were assessed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The experimental lattice constants deduced from XRD and TEM were compared with density functional theory-based calculated lattice constants using the Perdew–Burke–Ernzerhof exchange-correlation functional. We show that the calculated lattice constants are within 1–1.5% of the experimental values for the majority of the LnN species─a notable increase in accuracy over prior computational approaches. The frequencies of Raman scattering from the LO(Γ) phonon are reported across the series and compare well with published thin-film data on a smaller selection of the series. As expected, there is a linear relationship between the LO(Γ) phonon frequency and atomic number. Finally, we demonstrate that Raman spectroscopy can be used to detect the presence of a nanoscale oxide layer on the surface of ErN powders.