Charge-carrier behavior in Ba-, Sr- and Yb-filled CoSb3 : NMR and transport studies

Abstract

We report 59 Co NMR and transport measurements on n-type filled skutterudites BaxYbyCo4Sb12 and AxCo4Sb12 (A= Ba, Sr), promising thermoelectric materials. The results demonstrate consistently that a shallow defect level near the conduction band minimum dominates the electronic behavior, in contrast to the behavior of unfilled CoSb3. To analyze the results, we modeled the defect as having a single peak in the density of states, occupied at low temperatures due to donated charges from filler atoms. We fitted the NMR shifts and spin-lattice relaxation rates allowing for arbitrary carrier densities and degeneracies. The results provide a consistent picture for the Hall data, explaining the temperature dependence of the carrier concentration. Furthermore, without adjusting model parameters, we calculated Seebeck coefficient curves, which also provide good consistency. In agreement with recently reported computational results, it appears that composite native defects induced by the presence of filler atoms can explain this behavior. These results provide a better understanding of the balance of charge carriers, of crucial importance for designing improved thermoelectric materials. SbCo guest atom or unfilled site FIG. 1. Crystal structure of filled skutterudites, M zT4X12 , where M is a guest atom (0 z 1).information about the electronic behavior and the importance of defects, very close in energy to the conduction band edge in these n-type filled skutterudites. II. SAMPLE PREPARATION AND EXPERIMENTAL METHODSSkutterudites (space group Im3, shown in Fig. 1, visualized with VESTA [19]) of nominal composition Ba 0.1 Yb 0.2 Co 4 Sb 12 , Ba 0.2 Co 4 Sb 12 , and Sr 0.2 Co 4 Sb 12were prepared by a melting-annealing-spark plasma sintering method. The high-purity elements were weighed and mixed in the stoichiometric ratio, loaded into graphite-coated quartz tubes, and sealed in vacuum. These were placed in a furnace and heated to 1373 K at

Optimization of the Thermoelectric Performances of CoSbS Semiconductors Using the High-Pressure Fabrication Method

“…Thus, the analysis of the electrical behavior inside a material involves a detailed description of the behavior of electrons and holes. Electron thermal conductivity describes the thermal conductivity, which can be solved by Wiedemann-Franz law [9].…”

Electric and Thermoelectric Properties of Cu₁₂Sb₄S₁₃ Tetrahedrite with Impurities

“…Recently, several studies focused on multiple-filled skutterudites [13,14]. Xun Shi et al, [14] reported that there are a few doped samples which show an improved figure of merit of 1.7 at around 850 K. This ZT is one of the highest 25 value reported in skutterudites type of TE materials.…”

“…13 crystallize in a cubical form with space group of 217(I43m)wherein half of the Cu atoms occupy four-coordinate distorted tetrahedral sites 100 (Cu1) and other half occupy three-coordinate triangular sites (Cu2) with total 58 atoms per unit cell. Therefore, half of 24 Cu sites are occupied by twelve Cu-I sites and other half by twelve Cu-II sites.Figure 1shows the calculated density of states.…”

Half-Heusler thermoelectric materials: NMR studies

“…ZrCoSb-based materials have also been widely studied and shown promising zT and low thermal conductivity [4]. To better understand the mechanism and further improve thermoelectric performance, the NMR technique can be used as a local probe to reveal information about electronic properties, phonon behaviors and native defects [5,6,7]. In this work, we have applied NMR in studying members of this series of transition-metal-based half-Heusler materials, focusing in particular on trends in the electronic properties in this thermoelectric materials family.…”