Optical Properties of Filled Skutterudite ThFe_4P_(12)

Full-PotentiaJ Linearized Augmented Plane Wave plus locaJ orbital method （FPLAPW ＋10） calculations are performed for ThFe4P12 in the filled skutterudite in order to investigate the optical properties and to show the origin of the different optical transitions. It is found that the band gap is indirect for ThFe4P12. Then the contributions of the different transition peaks are analyzed from the imaginary part of the dielectric function. In contrast to recent experimental expectations, our calculations are in good agreement with experimental reflection spectra and ε1 （ω） spectrum.

Effect of Ba Filling Fraction on Thermoelectric Properties of p-type Ba_yFe_(1.6)Co_(2.4)Sb_(12)

Effects of Ba filling fraction on the thermoelectric properties of p type filled skutterudite compounds Ba yFe 1.6 Co 2.4 Sb 12 (y=0-0.63) were investigated.Ba yFe 1.6 Co 2.4 Sb 12 showed p type conduction.The hall coefficient (R H) and seebeck coefficient(α) increased with increasing Ba filling fraction.But hole concentration (p) and electrical conductivity (σ) decreased.While Ba filling fraction was about 0.4,the lattice thermal conductivity (κ L) reached the minimum value.The results show that effect of Ba rattling on phonon scattering is the strongest as Sb icosahedron partial voids are filled by Ba.A maximum dimensionless thermoelectric figure of merit (ZT) value of 0.7 was obtained for Ba 0.38 Fe 1.6 Co 2.4 Sb 12 at 750K.

Dual occupations of sulfur induced band flattening and chemical bond softening in p-type S_(y)Co_(4)Sb_(12-2y)S_(2y) skutterudites

The electronegative filling in skutterudites not only broadened the scope of filling atoms,but also facilitated the preparation of p-type skutterudites.However,the introduction of a single sulfur atom in the Co_(4)Sb_(12) cannot be achieved without charge compensation through the traditional equilibrium method.In the present study,the dual occupations of S-atoms by self-charge compensation were shown as the most stable forms under high pressure,and a series of p-type S_(y)Co_(4)Sb_(12-2y)S_(2y) skutterudites was successfully prepared by high-pressure-high-temperature(HPHT)method.The electronic structures and transport properties of as-obtained materials were investigated,and the related mechanisms were explored.The results suggested that the presence of S-impurities led to flattening of the electronic band that led to a higher Seebeck coefficient.The S-doped Co_(4)Sb_(12) displayed lower elastic modulus,elastic constant,and Debye temperature,thus indicating the chemical bond softening in skutterudites.The thermal conductivities of S_(y)Co_(4)Sb_(12-2y)S_(2y) compounds reduced monotonously with the increase in Scontent.This study provides a new and promising avenue for optimizing the thermoelectric properties of p-type Co_(4)Sb_(12).

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.

Research progress of p-type Fe-based skutterudite thermoelectric materials

Filled skutterudite is currently one of the most promising intermediate-temperature thermoelectric(TE)materials,having good thermoelectric transport performance and excellent mechanical properties.For the preparation of high-efficiency filled skutterudite TE devices,it is important to have p-and n-type filled skutterudite TE materials with matching performance.However,the current TE properties of p-type Fe-based filled skutterudite materials are worse than n-type filled skutterudite materials.Therefore,how to obtain high-performance p-type Fe-based filled skutterudite materials is the key to preparation of high-efficiency skutterudite-based TE devices.This review summarizes some methods for optimizing the thermal transport performance of p-type filled skutterudite materials at the atomic-molecular and nano-mesoscopic scale that have been used in recent years.These methods include doping,multi-atom filling,and use of low-dimensional structure and of nanocomposite.In addition,the synergistic optimization methods of the electrical and thermal transport parameters and advanced preparation technologies of p-type filled skutterudite materials in recent years are also briefly summarized.These optimizational methods and advanced preparation technologies can significantly improve the TE properties of p-type Fe-based filled skutterudite materials.

Creep behavior and post-creep thermoelectric performance of the n-type Skutterudite alloy Yb_(0.3)Co_(4)Sb_(12)

Upon uniaxial compressive loading at 500℃(T/Tm=0.67,where Tm is the absolute melting point),the n-type Skutterudite alloy Yb03Co4Sb12 deforms plastically by creep via a power-law,with a stress exponent~3 consistent with dislocation viscous glide.An activation energy of 171 kJ/mol is measured over the temperature range of 500-587℃(T/Tm=0.67-0.75)at a stress of 30 MPa.Yb_(0.3)Co_(4)Sb_(12)is ductile at 500℃,exhibiting a compressive strain of 25%when subjected to stresses ranging from 22 to 90 MPa for up to 28 days.Among the thermoelectric materials tested so far for creep,Yb_(0.3)Co_(4)Sb_(12)exhibits a creep resistance intermediate between low-melting(Bi2Te3,TAGS-85)and high-melting thermoelectrics(Mg2Si and ZrNiSn).A relatively modest drop in the figure of merit zT,from 0.67 to 0.52,is displayed by Yb_(0.3)Co_(4)Sb_(12)after accumulating 3.7%compressive creep strain at 500℃,mostly due to a drop in electrical conductivity.