Correlations between Structural and Electronic Properties in the Filled Skutterudite Sm_y(Fe_xNi_1–x)₄Sb₁₂

Abstract

A structural study of the filled skutterudite Smy(FexNi1-x)4Sb12 was performed by means of X-ray powder diffraction and μ-Raman spectroscopy with the aim to unveil the correlations between structural and electronic properties of this material and to favor the improvement of its thermoelectric performance. Samples were prepared by direct reaction of the elements at 1223 K, followed by quenching and subsequent sintering at 873 K; microstructure and composition of the obtained products were determined by SEM-EDS. The position of the boundary separating regions that obey hole- and electron-based conduction mechanisms was found by X-ray diffraction at x ≈ 0.63 and y ≈ 0.30, confirmed by measurements of room-temperature Seebeck coefficient, and discussed on the basis of crystallographic data. The presence of a discontinuity is observed in several structural and spectroscopic parameters at the p/n crossover; it is interpreted as associated with the change in the conduction mechanism. The role of the rare earth filling fraction in driving the structural response of the material is investigated too. The advantage of using X-ray diffraction and μ-Raman spectroscopy as aids in the study of electronic properties of this material is highlighted, as well as the complementarity of the two techniques.

Effect of Different Processing Routes on the Power Factor of the Filled Skutterudite Sm (Fe Ni ) Sb (x = 0.50-0.80; y = 0.12-0.53)

“…x 1-x 4 12 electrons for <~0.63 and an electron deficiency for >~0.63 with x x respect to the electronic count of a compensated semiconductor, thus suggesting the -character of the former compositions and the -n p character of the latter. As aforementioned, relying on structural data, Fe63 results to be located close to the / crossover; therefore, the 16 p n positive Seebeck coefficients appearing in Fig. 8 b) could at a first glance seem to contradict this conclusion.…”

“…Small pieces of pure elements Fe (Alfa-Aesar, 99.99 wt.%), Ni (Alfa-Aesar, 99.99 wt.%), Sm (NewMet, 99.9 wt.%) and Sb (Mateck, 99.99 wt.%) were weighed in due amounts and placed into a quartz tube subsequently sealed under vacuum; the starting mixture was treated at 1223 K for 3 hours, and then quenched in a salted iced water bath. The Sm amount to be employed was calculated taking into 16 account results obtained in; Sb was used in a slight excess to avoid possible leakage caused by its considerable vapour pressure (0.133 Pa at 873 K). As-cast samples were then annealed in vacuum at 873 K for 7 days.…”

“…Being S, S and S the overall, electron and hole Seebeck where m is the electron mass and n the number of charge carriers. e Therefore, due to the described involvement of mobilities, the p/n crossover is better identified by the composition at which S assumes the 16 maximum value. In this respect, as shown both in this work and in, Seebeck coefficients of Fe63 are generally higher than for both the other samples, meaning that the cited composition is located close to the p/n transition.…”

“…The X icosahedral cage built around the 2a site is of the utmost 12 importance, due to its ability to host atoms such as alkaline-earths or lanthanides, responsible for lowering the phononic part of thermal conductivity and for determining the n-or p-conduction regime of the resulting material. Electrons contributed by the filler ion, in fact, tune the electronic count of the skutterudite; previous studies indicated the 16 p/n crossover in Sm (Fe Ni ) Sb to be located at x ~ 0.63. It is 4 12 noteworthy that the filler amount (y) can hardly be forced to a certain desired value, being it strictly correlated to the electronic count determined by the Fe/Ni ratio.…”

Thermoelectric Properties of In<i>_x</i>FeCo₃Sb₁₂ Consisting Mainly of In-Filled <i>p</i>-Type Skutterudites

“…These atoms, called as llers, were reported to have variation such as alkali metals 9,10) and rare-earth elements. [11][12][13] Notably ller atoms produce optical phonon branches at low energy, and sometimes causes anharmonic oscillation to greatly reduce the lattice thermal conductivity.…”