Effect of partial void filling on the transport properties of Nd_xCo₄Sb₁₂skutterudites

Abstract

Polycrystalline samples of the partially filled skutterudites NdxCo4Sb12 have been prepared and characterized by x-ray powder diffraction and differential thermal analysis. The saturation limit of the Nd void filling in CoSb3 was found to be around 13%. All samples decompose incongruently at a temperature of 1149 ± 6 K. Room temperature Hall measurements show that each Nd atom donates approximately 0.8 electrons, which is significantly less than the Nd oxidation state (3+). The temperature dependence of the electrical and thermal transport properties has been measured over the range of 11–700 K. The electrical resistivity and absolute value of the Seebeck coefficient decrease with increasing Nd content and for samples with x > 0.02 the temperature dependence is typical of heavily doped semiconductors. Filling CoSb3 with Nd causes a rapid initial decrease in the lattice thermal conductivity with a minimum at the composition Nd0.1Co4Sb12. Nd-filled skutterudites exhibit the lowest value of the lattice thermal conductivity in comparison with other partially filled skutterudites at x < 0.1, which could be attributed to a smaller radius of Nd than that of other filling elements. At high temperature the ZT value of the Nd-filled skutterudites is limited due to intrinsic conduction caused by the relatively low carrier concentration. The effect of the partial Nd filling on the transport properties of the filled skutterudite compounds is discussed in the context of potential thermoelectric materials.

Effect of partial La filling on the local electronic properties of LaxCo4Sb12studied using59Co NMR

“…In x = 0.1, a weak impurity peak appears (denoted by an asterisk in figure 2(a)), while it has little effect on the NMR measurements. In x = 0.1 and 0.2, the exceptionally large atomic displacement parameters (ADPs) of La compared with those of Co and Sb were suggested to be a characteristic of the rattling of the filler atoms at this rattler site [3]- [10]. Our attempts to reduce these ADPs by displacing La to the other crystallographic sites with a lower site symmetry resulted in otherwise unstable refinements, confirming the rattling nature of La (large ADPs) at this site.…”

“…These voids can be filled by various elements such as Ca, Sr, La and Ce so as to form the so-called filled skutterudites M x Co 4 Sb 12 (where M is the filler atom and x is the partial filling fraction) [2]. In M x Co 4 Sb 12 , the lattice thermal conductivity (κ L ) could be significantly reduced because of the scattering of the thermal phonons by the rattling of the filler atoms [3]- [10]. This reduced κ L readily leads to improvement of the thermoelectric performance according to the thermoelectric figure of merit Z = S 2 σ/κ, where S, σ and κ are the Seebeck coefficient, electrical conductivity and total thermal conductivity, respectively.…”

High-temperature electrical and thermal transport properties of fully filled skutterudites RFe4Sb12 (R = Ca, Sr, Ba, La, Ce, Pr, Nd, Eu, and Yb)

“…13,14 After that, improving the thermoelectric figure of merit in ntype skutterudites gained keen interest in the next decade. Various n-type single element filled R y Co 4 Sb 12 skutterudites with high ZT values were reported, 15,16 showing great potentials as thermoelectric power generator used at high temperatures. Moreover, recently, filling two or more types of fillers into the voids in skutterudite have been shown to be able to further reduce lattice thermal conductivity and improve ZT to 1.4 in double-filled and 1.7 in multiple-filled n-type skutterudites.…”

How thermoelectric properties of p-type Tl-filled skutterudites are improved

“…These compounds crystallize in a body-centered cubic structure (Im3 space group) with 32 atoms in the unit cell. The unit cell contains two structural cages that can be filled by a variety of guest atoms such as rare earth elements, [4][5][6][7] alkaline earth metals, [8][9][10] alkali metals, 11,12 and group 13 elements. [13][14][15][16][17] When the guest atom denoted by R is incorporated into the cages, the general formula of the compounds, referred to as filled skutterudites, becomes RM 4 × 12 .…”