Electronic Structure and Core Spectroscopy of Scandium Fluoride Polymorphs

Microscopic knowledge of the structural, energetic, and electronic properties of scandium fluoride is still incomplete despite the relevance of this material as an intermediate for the manufacturing of Al-Sc alloys. In a work based on first-principles calculations and X-ray spectroscopy, we assess the stability and electronic structure of six computationally predicted ScF3 polymorphs, two of which correspond to experimentally resolved single-crystal phases. In the theoretical analysis based on density functional theory (DFT), we identify similarities among the polymorphs based on their formation energies, chargedensity distribution, and electronic properties (band gaps and density of states). We find striking analogies between the results obtained for the low- and high-temperature phases of the material, indirectly confirming that the transition occurring between them mainly consists of a rigid rotation of the lattice. With this knowledge, we examine the X-ray absorption spectra from the Sc and F K-edge contrasting firstprinciples results obtained from the solution of the Bethe-Salpeter equation on top of all-electron DFT with high-energy-resolution fluorescence detection measurements. Analysis of the computational results sheds light on the electronic origin of the absorption maxima and provides information on the prominent excitonic effects that characterize all spectra. A comparison with measurements confirms that the sample is mainly composed of the high- and low-temperature polymorphs of ScF3. However, some fine details in the experimental results suggest that the probed powder sample may contain defects and/or residual traces of metastable polymorphs.

Automated summary

In this study, the stability and electronic structure of six ScF3 polymorphs were evaluated using first-principles calculations and X-ray spectroscopy. The results showed the transition between low- and high-temperature phases mainly consists of a rigid rotation of the lattice. Analysis of the computational results provided insights into the electronic origin of the absorption maxima and the excitonic effects in the spectra. Comparison with experimental measurements confirmed the presence of high- and low-temperature polymorphs, but also suggested the presence of defects or residual traces of metastable phases in the sample.