Electron energy loss spectroscopy of the ${\text{L}}_{2,3}$ edge of phosphorus skutterudites and electronic structure calculations

In this study we report the results of experiments and theoretical calculations on the phosphorus ${\text{L}}_{2,3}$ edges of the skutterudites ${\text{CoP}}_3$, ${\text{LaFe}}_4{\text{P}}_{12}$, ${\text{NiP}}_3$, ${\text{RhP}}_3$, and ${\text{IrP}}_3$. Phosphorus $s$ and $d$ density of states above the Fermi level was studied by transmission electron energy loss spectroscopy while theoretical calculations were performed using both a real-space multiple-scattering procedure and density-functional theory. Generally, there are good agreements between both types of calculations and the experimental results. The near-edge structure of all the examined compounds shows the same overall features, including the metallic ${\text{NiP}}_3$ and the metallic filled skutterudite ${\text{LaFeP}}_{12}$, and is well explained by comparison to phosphorus density of states. We also discuss the similarities to previously reported results on $\text{Si}{\text{L}}_{2,3}$ edges and interpret the differences of the various skutterudites in terms of the electronegativities of the involved atom species.

Figure 1

(Color online) The unfilled skutterudite structure. Phosphorus and transition metals are depicted as dark (red) and bright (yellow), respectively. The semi-tetrahedral arrangement of a phosphorus atom is shown with lines.

Figure 2

(Color online) (a) Experimental ${\text{LaCoO}}_3$ $\text{La}{N}_{4,5}$ edge (thin solid/black line) used for subtracting the La edge from ${\text{LaFe}}_4{\text{P}}_{12}$ and (b) ${\text{LaFe}}_4{\text{P}}_{12}$ $\text{P}{\text{L}}_{2,3}$ edge before (thin solid/black line) and after (thick solid/blue line) subtracting the $\text{La}{N}_{4,5}$ edge. The edge was extracted by fitting an exponential (short-dashed/red line) to the right-hand side of the La peak in both spectra and then normalizing and subtracting the rest from the ${\text{LaCoO}}_3$ spectrum (long-dashed/blue line) from the ${\text{LaFe}}_4{\text{P}}_{12}$ spectrum.

Figure 3

Experimental P edges (solid lines) compared to edges simulated by Feff8 (dashed lines) with core hole for (a) ${\text{CoP}}_3$, (b) ${\text{LaFe}}_4{\text{P}}_{12}$, (c) ${\text{NiP}}_3$, (d) ${\text{RhP}}_3$, and (e) ${\text{IrP}}_3$.

Figure 4

(Color online) Comparison of experimental ELNES curves and electronic $\text{P}s$, $p$ and $d$ states from DFT calculations. From top to bottom: (a) ${\text{CoP}}_3$, (b) ${\text{LaFe}}_4{\text{P}}_{12}$, (c) ${\text{NiP}}_3$, (d) ${\text{RhP}}_3$, and (e) ${\text{IrP}}_3$. Experimental near-edge structure (thick/black line), $\text{P}s$ (thin solid/red line), $p$ (dotted/yellow line), and $d$ (dot-dashed/green line) states. The thick-dashed/blue line shows the 1:1 sum of $\text{P}s$ and $d$ states smeared to an energy resolution of 1.5 eV.