Achieving superior performance in thermoelectric Bi_(0.4)Sb_(1.6)Te_(3.72)by enhancing texture and inducing high-density line defects

Miniaturization of efficient thermoelectric(TE)devices has long been hindered by the weak mechanical strength and insufficient heat-to-electricity conversion efficiency of zone-melted(ZM)ingots.Here,we successfully prepared a robust high-performance p-type Bi_(0.4)Sb_(1.6)Te_(3.72)bulk alloy by combining an ultrafast thermal explosion reaction with the spark plasma sintering(TER-SPS)process.It is observed that the introduced excess Te not only enhances the(00l)-oriented texture to ensure an outstanding power factor(PF)of 5 mW m^(−1)K^(−2),but also induces extremely high-density line defects of up to 10^(11)–10^(12)cm^(−2).Benefiting from such heavily dense line defects,the enhancement of the electronic thermal conductance from the increased electron mobility is fully compensated by the stronger phonon scattering,leading to an evident net reduction in total thermal conductivity.As a result,a superior ZT value of~1.4 at 350 K is achieved,which is 40%higher than that of commercial ZM ingots.Moreover,owing to the strengthening of grain refinement and highdensity line defects,the mechanical compressive stress reaches up to 94 MPa,which is 154%more than that of commercial single crystals.This research presents an effective strategy for the collaborative optimization of the texture,TE performance,and mechanical strength of Bi2Te3-based materials.As such,the present study contributes significantly to the future commercial development of miniature TE devices.

On the tuning of electrical and thermal transport in thermoelectrics: an integrated theory–experiment perspective

During the last two decades,we have witnessed great progress in research on thermoelectrics.There are two primary focuses.One is the fundamental understanding of electrical and thermal transport,enabled by the interplay of theory and experiment;the other is the substantial enhancement of the performance of various thermoelectric materials,through synergistic optimisation of those intercorrelated transport parameters.Here we review some of the successful strategies for tuning electrical and thermal transport.For electrical transport,we start from the classical but still very active strategy of tuning band degeneracy(or band convergence),then discuss the engineering of carrier scattering,and finally address the concept of conduction channels and conductive networks that emerge in complex thermoelectric materials.For thermal transport,we summarise the approaches for studying thermal transport based on phonon–phonon interactions valid for conventional solids,as well as some quantitative efforts for nanostructures.We also discuss the thermal transport in complex materials with chemical-bond hierarchy,in which a portion of the atoms(or subunits)are weakly bonded to the rest of the structure,leading to an intrinsic manifestation of part-crystalline part-liquid state at elevated temperatures.In this review,we provide a summary of achievements made in recent studies of thermoelectric transport properties,and demonstrate how they have led to improvements in thermoelectric performance by the integration of modern theory and experiment,and point out some challenges and possible directions.

Grain boundary engineering with nano-scale InSb producing high performance In_(x)Ce_(y)Co_(4)Sb_(12+z)skutterudite thermoelectrics

Thermoelectric semiconductors based on CoSb_(3)hold the best promise for recovering industrial or automotive waste heat because of their high efficiency and relatively abundant,lead-free constituent elements.However,higher efficiency is needed before thermoelectrics reach economic viability for widespread use.In this study,n-type In_(x)Ce_(y)Co_(4)Sb_(12+z)skutterudites with high thermoelectric performance are produced by combining several phonon scattering mechanisms in a panoscopic synthesis.Using melt spinning followed by spark plasma sintering(MS-SPS),bulk In_(x)Ce_(y)Co_(4)Sb_(12+z)alloys are formed with grain boundaries decorated with nano-phase of InSb.The skutterudite matrix has grains on a scale of 100-200 nm and the InSb nano-phase with a typical size of 5e15 nm is evenly dispersed at the grain boundaries of the skutterudite matrix.Coupled with the presence of defects on the Sb sublattice,this multi-scale nanometer structure is exceptionally effective in scattering phonons and,therefore,InxCey-Co_(4)Sb_(12)/InSb nano-composites have very low lattice thermal conductivity and high zT values reaching in excess of 1.5 at 800 K.

Rapid fabrication and thermoelectric performance of SnTe via non-equilibrium laser 3D printing

Thermoelectric technologies based on Seebeck and Peltier effects, as energy techniques able to directly convert heat into electricity and vice versa, hold promise for addressing the global energy and environmental problems. The development of efficient and low-cost thermo- electric modules is the key to their large-scale commercial applications. In this paper, using a non-equilibrium laser 3D printing technique, we focus an attention on the fabrication of mid-temperature p-type SnTe thermoelectric materials. The influence of laser power, scanning speed and layer thickness on the macro-defects, chemical and phase composition, microstructure and thermoelectric performance was systematically investigated. First and foremost, the processing parameter window for printing a highquality layer is determined. This is followed by the finite element method used to simulate and verify the influence of the laser-induced molten pool temperature distribution on the final composition and microstructure. Finally, the high-performance SnTe layer with 10 mm × 10 mm in area is produced within seconds with room temperature Seebeck coefficient close to that of SnTe manufactured by the traditional methods. Consequently, this work lays a solid foundation for the future fabrication of thermoelectric modules using laser non-equilibrium printing techniques.

A comprehensive review on Bi_(2)Te_(3)-based thin films: Thermoelectrics and beyond

Bi_(2)Te_(3)-based materials are not only the most important and widely used room temperature thermoelectric(TE)materials but are also canonical examples of topological insulators in which the topological surface states are protected by the time-reversal symmetry.High-performance thin films based on Bi_(2)Te_(3)- have attracted worldwide attention during the past two decades due primarily to their outstanding TE performance as highly efficient TE coolers and as miniature and flexible TE power generators for a variety of electronic devices.Moreover,intriguing topological phenomena,such as the quantum anomalous Hall effect and topological superconductivity discovered in Bi_(2)Te_(3)-based thin films and heterostructures,have shaped research directions in the field of condensed matter physics.In Bi_(2)Te_(3)-based films and heterostructures,delicate control of the carrier transport,film composition,and microstructure are prerequisites for successful device operations as well as for experimental verification of exotic topological phenomena.This review summarizes the recent progress made in atomic defect engineering,carrier tuning,and band engineering down to a nanoscale regime and how it relates to the growth and fabrication of high-quality Bi_(2)Te_(3)-based films.The review also briefly discusses the physical insight into the exciting field of topological phenomena that were so dramatically realized in Bi_(2)Te_(3)-and Bi_(2)Se_(3)‐based structures.It is expected that Bi_(2)Te_(3)-based thin films and heterostructures will play an ever more prominent role as flexible TE devices collecting and converting low-level(body)heat into electricity for numerous electronic applications.It is also likely that such films will continue to be a remarkable platform for the realization of novel topological phenomena.