Comparison of theoretical and experimental dielectric functions: Electron energy-loss spectroscopy and density-functional calculations on skutterudites

Abstract

We explore the possibility of combining density functional theory ͑DFT͒ and electron energy loss spectroscopy ͑EELS͒ to determine the dielectric function of materials. As model systems we use the skutterudites CoP 3 , CoAs 3 , and CoSb 3 which are prototypes for thermoelectric materials. We achieve qualitative agreement between the theoretically and experimentally obtained low energy-loss spectra and dielectric function. Some of the remaining discrepancies may be caused by the challenge of refining the experimental spectra before Kramers-Kronig analysis. However, contrary to what is the case for some crystals with less complicated electronic structure, the DFT calculated plasmon energies deviate significantly from the experimental values. The great accuracy with which the plasmon energy can be determined by EELS, suggests that this technique may provide valuable inputs in further efforts to improve DFT calculations. The use of EELS as the experimental technique may become particularly powerful in studies of small volumes of materials.

Transition metald-band occupancy in skutterudites studied by electron energy-loss spectroscopy

“…The Dudkin model is generally confirmed by site-and symmetry-projected density of states from DFT calculations. Typically, a large overlap between the TM 3d and Pn 3p states is observed, 7,9,32 indicating bonding through hybridization.…”

“…2 Tailoring their electronic and thermal properties is therefore possible, and modified skutterudite materials are indeed among the most promising of a new generation of thermoelectric materials. [2][3][4] Several theoretical [5][6][7][8] and experimental [9][10][11][12][13] studies of the electronic structure of Cobased skutterudites have been performed. A particular interesting signature of the bonding and electronic structure is the occupancy of the 3d states of Co. Anno et al 12 used x-ray photoelectron spectroscopy ͑XPS͒ to study the occupied states of CoAs 3 and CoSb 3 .…”

Characterization of nickel silicides using EELS‐based methods

“…Thus, transition metals usually display a single, broad plasmon peak, and the Drude model often fails to predict their plasmon energies. This is opposed to simple metals such as Na, Al and semiconductors such as Si, Ge, which have sharp plasmon peaks near the predicted value (Prytz et al, 2006). An alternative mechanism of energy loss, involving the transfer of energy from a transmitted electron to a single atomic electron within the specimen is also very common for this type of materials.…”

“…For electrons close to the Fermi level, this second mechanism can be regarded as competing with plasmon excitation and is coupled to it. The possible effects of single-electron excitation include broadening and/or shift of the plasmon peak and the addition of fine structure (Egerton, 1986;Prytz et al, 2006).…”

One-Step Synthesis and Sintering of Skutterudite CoSb3: Smart Houses Materials?

“…However, in the second method the Seebeck coefficient changes to positive approximately at 540 K. The reason is that the hole mobility is much larger than the electron mobility in the temperature range higher than 540 K [12], at which intrinsic excitation commences. It has been reported that the intrinsic CoSb3 shows the p-type conductivity [13,14]. In this study, the low purity of Co (99.8%) may be the reason for the appearance of n-type conductivity initially [15].…”