P-type silicon germanium (SiGe) alloys, Si80Ge20B0.6, with homogeneously dispersed SiC nanoparticles were prepared by ball milling and subsequent spark plasma sintering. The influence of grain size reduction of SiGe matrix and SiC nanoparticle dispersion on electrical and thermal transport properties were investigated. A significant reduction in lattice thermal conductivity is achieved by a more pronounced grain boundary scattering of phonons introduced by grain size reduction after ball milling. Dispersing SiC nanoparticles in the Si80Ge20B0.6 matrix effectively reduces the conduction of heat by providing additional phonon scattering centers. A dimensionless figure-of-merit (ZT) of 0.62 at 1000 K is obtained in nanostructuring Si80Ge20B0.6 incorporated with only 0.5vol% SiC nanoparticles, which is 17% higher than the parent Si80Ge20B0.6 matrix and about 30% higher than p-type SiGe alloy used in the radioisotope thermoelectric generator in space missions.
The cost-effective fabrication of CoSb3-based filled skutterudites (SKD) thermoelectric materials is a bottleneck issue preventing their successful commercial application. In this study, we employed a simple and scalable process to simultaneously produce a rapid formation and consolidation of n-type filled skutterudites. This method, consisting of RF-induction melting, quenching and spark plasma sintering (SPS), required less than a half-hour, significantly shorter than conventional process of furnace melting (over 24 h), annealing (about one week) and SPS. The fabricated bulk SKD materials possessed homogeneous composition and structures with a good thermoelectric performance which are analogous to those materials fabricated according to a conventional process. The homogeneous microstructures and phase composition distribution which was a result of the simultaneously proceeded rapid reaction and densification of the grinding-destructed dendrite networks of the Sb/CoSb/CoSb2 peritectic structure formed in the RF-induction melting and quenching. The good thermoelectric TE performance and the very low consumption of process time and energy would make this simple process a potential and practical method for industrial-level mass production of filled skutterudite thermoelectric materials.
Diamond-like CuInTe2 compound has attracted great attentions recently as a new thermoelectric material. Despitethe considerable thermoelectric performance, the relatively high thermal conductivity at low and medium temperature ranges restricted further improvement of thermoelectric performance. Alloying was demonstrated an effective way to introduce mass and strain fluctuationsto lower the lattice thermal conductivity in several typical thermoelectric materials. In this work, CuInTe2-xSx (x=0, 0.05, 0.1, 0.15) solid solutions were fabricated by melting and annealing techniques. Phase purity and element distribution were examined by XRD and SEM-EDS measurements respectively. All the samples were pure phase and all the elements were distributed homogeneously. Callaway model was employed to analyze the thermal transport. It isfound that S substitution minimized the lattice thermal conductivity effectively, mainly due to extra phonon scattering induced by strain field fluctuation. However, itselectricalproperties were deteriorated by S doping, probably due to bigger band gap in CuInS2 than in CuInTe2.Therefore, if the electrical properties being improved by element doping, the CuInTe2-xSx (x=0, 0.05, 0.1, 0.15) solid solutions will achieve high thermoelectric performance.
Interface stability is one of the key issues determining the service reliability and life of thermoelectric devices. For skutterudite-based thermoelectric devices, the barrier layer is required in order to restrain the inter-diffusion between the hot-side electrode and skutterudite matrix. In this work, Ti88Al12 was selected as the barrier layer. N-type Yb0.3Co4Sb12/Ti88Al12/Yb0.3Co4Sb12 and p-type CeFe3.85Mn0.15Sb12/Ti88Al12/CeFe3.85Mn0.15Sb12 thermoelectric joints were prepared by one-step hot pressing sintering method. The evolution processes of contact resistivity and microstructure were studied through accelerated aging experiments. The results show that the contact resistivity of n-type joints increases slower than that of p-type joints under the same aging condition. Activation energy for n-type and p-type joints is 84.1 kJ/mol and 68.8 kJ/mol, respectively. Growth of the inter-metallic compound layer and cracking at the AlCo/TiCoSb interface result in rapidly increased contact resistivity of n-type joints. For p-type joints, the difference of coefficient of thermal expansion between CeFe3.85Mn0.15Sb12 and Ti88Al12 becomes the main reason for the cracks.
Thermoelectric (TE) power generation technology is highly expected for various applications such as special power supply, green energy, energy harvesting from the environment and harvesting of industrial waste heat. Over the past years, the record of zT values of TE materials has been continuously updated, which would bode well for widespread practical applications of TE technology. However, the TE device as the core technology for the TE application lags behind the development of TE materials. Especially, the large-scale application of TE power generation technology is facing bottlenecks and new challenges. This reviewpresents an overview of the recent progress on TE device design and integration with particular attentions on device optimization design, electrode fabrication, interface engineering, and service behavior. The future challenges and development strategies for large-scale application ofthermoelectric power generation are also discussed.
