Synthesis and Thermoelectric Properties of Charge-Compensated SyPdxCo4-xSb12 Skutterudites

Enhancement in Thermoelectric Performance in Ti-doped Yb0.4Co4Sb12 Skutterudites via Carrier Optimization and Phonon Anharmonicity

Yb0.4Co4Sb12, being a well-studied system, has shown notably high thermoelectric performance due to the Yb filler atom-driven large concentration of charge carriers and lower value of thermal conductivity. In this work, the thermoelectric performance of YbzCo4-xTixSb12 (where z = 0, x = 0 and z = 0.4, x = 0, 0.04, and 0.08) upon Ti doping prepared by the melt-quenched-annealing followed by spark plasma sintering (SPS) has been studied in the temperature range of 300-700 K. Addition of Yb and doping of donor Ti at the Co site simultaneously increase the electrical conductivity to 1453.5 S/cm at 300 K, which ultimately boosts the power factor as high as ∼4.3 mW/(m·K2) at 675 K in Yb0.4Co3.96Ti0.04Sb12. Adversely, a significant reduction in thermal conductivity is obtained from ∼7.69 W/(m·K) (Co4Sb12) to ∼3.50 W/(m·K) (Yb0.4Co3.96Ti0.04Sb12) at ∼300 K. As a result, the maximum zT is achieved as ∼0.85 at 623 K with high hardness of 584 HV for the composition of Yb0.4Co3.96Ti0.04Sb12, which demonstrates it to be an efficient material suitable for intermediate temperature thermoelectric applications.

Research Progress on Preparation Methods of Skutterudites

Thermoelectric material is a new energy material that can realize the direct conversion of thermal energy and electric energy. It has important and wide applications in the fields of the recycling of industrial waste heat and automobile exhaust, efficient refrigeration of the next generation of integrated circuits and full spectrum solar power generation. Skutterudites have attracted much attention because of their excellent electrical trGiovanna Latronicoansport performance in the medium temperature region. In order to obtain skutterudites with excellent properties, it is indispensable to choose an appropriate preparation method. This review summarizes some traditional and advanced preparation methods of skutterudites in recent years. The basic principles of these preparation methods are briefly introduced. Single-phase skutterudites can be successfully obtained by these preparation methods. The study of these preparation methods also provides technical support for the rapid, low-cost and large-scale preparation of high-performance thermoelectric materials.

Synthesis Optimization and Thermoelectric Properties of S-Filled and Te-Se Double-Substituted Skutterudite under High Pressure

In recent years, skutterudite filled with electronegative elements (S, Se, Cl, Br) has attracted the extensive attention of researchers. By doping electron donors (Pb, Ni, or Te, S, Se) at the Co or Sb sites, the electronegative elements can form thermodynamically stable compounds in the intrinsic pores of the skutterudite, substantially expanding the research scope of skutterudite. In this study, S_0.05Co₄Sb_11.3Te_0.6Se_0.1 skutterudite was synthesized at high pressure and high temperature, with a pressure range of 2.0-3.5 GPa. The phase composition, micro-morphology, and electrical and thermal transport properties were systematically characterized. The micromorphology analysis shows that the introduction of S element and substituting Te and Se at the Sb sites inhibit the grain growth in a suitable high-pressure environment. Substantial differences are observed in the directions of the lattice stripes in the samples, and rich grain boundaries and many lattice distortions and dislocation defects occur. The carrier concentration can be optimized by filling the voids of the skutterudite with a few S atoms, and the thermoelectric properties can be optimized by scattering phonons through resonance scattering and defect scattering. The samples synthesized at a pressure of 3.0 GPa and a temperature of 900 K have a maximum power factor of 23.85 × 10^-4 W m^-1 K^-2 and a maximum zT value of 1.30 at a test temperature of 773 K.

Doubled Thermoelectric Figure of Merit in p-Type β-FeSi2 via Synergistically Optimizing Electrical and Thermal Transports

β-FeSi₂ has long been investigated as a promising thermoelectric (TE) material working at high temperatures due to its combining features of environmental friendliness, good thermal stability, and strong oxidation resistance. However, the real application of β-FeSi₂ is still limited by its low TE figure of merit (zT). In this study, nearly doubled zT in p-type β-FeSi₂ has been achieved via synergistically optimizing electrical and thermal transports. Based on the first-principles calculations, Al with shallow acceptor transition level and high carrier donation efficiency is chosen to dope β-FeSi₂. Significantly improved electrical transport, particularly in the low temperature range, has been obtained in the Al-doped β-FeSi₂ system. The power factor for FeSi_1.96Al_0.04 at 300 K is even higher than that of p-type β-FeSi₂-based compounds reported previously at high temperatures. By alloying β-FeSi₂ with Os at the Fe sites, we further lower the lattice thermal conductivity. Fe_0.80Os_0.20Si_1.96Al_0.04 possesses the lowest lattice thermal conductivity among the β-FeSi₂ compounds prepared by the equilibrium method. Finally, a record-high zT value of 0.35 is obtained for p-type Fe_0.80Os_0.20Si_1.96Al_0.04. This study is expected to accelerate the application of β-FeSi₂.

Tin Acceptor Doping Enhanced Thermoelectric Performance of n-Type Yb Single-Filled Skutterudites via Reduced Electronic Thermal Conductivity

Although introducing more fillers in nanocages is beneficial to gain low lattice thermal conductivity within filling fraction limit, accompanying high electronic thermal conductivity usually results in an unsatisfactory figure of merit ZT in CoSb₃. In this work, Sn is adopted to tailor the electronic transport behavior for a high-filled Yb_0.3Co₄Sb₁₂ alloy through rapid melt spinning combined with hot-press sintering processes. In spite of the reduced electrical conductivity, the power factors are scarcely influenced due to improved Seebeck coefficients by the reduced carrier concentration and moderate ionized impurity scattering. However, the lower total thermal conductivity is synergistically tuned by the effective suppression of electronic thermal conductivity and the low lattice thermal conductivity. As a result, both the high maximum ZT value of 1.4 at 823 K and the average ZT value of ∼0.98 between 300 and 850 K can be achieved in the Yb_0.3Co₄Sb_11.85Sn_0.15 sample. This work illustrates a promising approach for improving thermoelectric properties by largely tuning the electronic thermal conductivity.

Ga-Doping-Induced Carrier Tuning and Multiphase Engineering in n-type PbTe with Enhanced Thermoelectric Performance

P-type lead telluride (PbTe) emerged as a promising thermoelectric material for intermediate-temperature waste-heat-energy harvesting. However, n-type PbTe still confronted with a considerable challenge owing to its relatively low figure of merit ZT and conversion efficiency η, limiting widespread thermoelectric applications. Here, we report that Ga-doping in n-type PbTe can optimize carrier concentration and thus improve the power factor. Moreover, further experimental and theoretical evidence reveals that Ga-doping-induced multiphase structures with nano- to micrometer size can simultaneously modulate phonon transport, leading to dramatic reduction of lattice thermal conductivity. As a consequence, a tremendous enhancement of ZT value at 823 K reaches ∼1.3 for n-type Pb_0.97Ga_0.03Te. In particular, in a wide temperature range from 323 to 823 K, the average ZT_ave value of ∼0.9 and the calculated conversion efficiency η of ∼13% are achieved by Ga doping. The present findings demonstrate the great potential in Ga-doped PbTe thermoelectric materials through a synergetic carrier tuning and multiphase engineering strategy.