Effect of samarium filling on the lattice thermal conductivity of skutterudite materials

Sm-filled skutterudites SmxCo4Sb12 (x=0.1, 0.2, 0.5) were synthesized via high pressure and high temperature (HPHT) technique. The temperature dependences of electrical resistivity, Seebeck coefficient and thermal conductivity were measured on these compounds in the range of 300-723 K. All samples showed n-type conduction. The thermal conductivity of SmxCo4Sb12 was significantly depressed as com-pared to unfilled CoSb3. It was believed that Sm atoms "rattled" in the voids of structure and substantially affected the phonon propagation through the lattice. The dimensionless thermoelectric figure of merit, ZT, increased with increasing temperature and reached a maximum value of 0.81 for Sm0.5Co4Sb12 at 723 K.     

Effects of praseodymium doping on thermoelectric transport properties of CaMnO3 compound system

The rare earth Pr doped Ca1-x Prx MnO3(x=0,0.06,0.08,0.1,0.12,and 0.14) compound bulk samples were prepared to study the effect of Pr doping on thermoelectric transport properties of CaMnO3 compound system.The doped samples exhibited single phase composition within the experimental doping range,with condensed bulk microstructure and small porosities.The electrical resistivity was remarkably reduced for doped samples,on account of the enhanced carrier concentration;the absolute value of Seebeck coefficient was deteriorated mainly due to enhanced electron carrier concentration.The electrical performances of the doped samples reflected by resistivity and Seebeck coefficient fluctuations were optimistically tuned,with an optimized power factor value of 0.342 mW/(m·K2) at 873 K for x=0.08 sample,which was very much higher comparing with that of the un-doped sample.The lattice thermal conduction was really confined,leading to distinctly repressed total thermal conductivity.The thermoelectric performance was noticeably improved by Pr doping and the dimensionless figure of merit ZT for the Ca0.92 Pr0.08 MnO3 compound was favorably optimized with the maximum value 0.16 at 873 K.     

Zintl phase compounds AM2Sb2 （A=Ca,Sr, Ba,Eu, Yb;M=Zn,Cd） and their substitution variants：a class of potential thermoelectric materials

Zintl phase compounds AM2Sb2(A=Ca,Sr,Ba,Eu,Yb;M=Zn,Cd)is a new class of promising thermoelectrics owing to their intrinsic features in electronic and crystal structure,such as a small or even disappeared band-gap,large density-of-states at the Fermi level,covalently bonded network of M-Sb,as well as the layered stacking by cations A2+and anionic slabs(M2Sb2)2–.In addition,the rich solid-state chemistry of Zintl phase allows structural modification and chemical substitution to adjust the fundamental transport parameters(carrier concentration,mobility,effective mass,electronic and lattice thermal conductivity)for improving the thermoelectric performance.In the present review,the recent advances in synthesis and thermoelectric characterization of title compounds AM2Sb2were presented,and the effects of alloying or substitution for sites A,M and Sb on the electrical and thermal transport were emphasized.The structural disorder yielded by the incorporation of multiple ions significantly increased the thermoelectric figure of merit mainly resulted from the reduction of thermal conductivity without disrupting the carrier transport region in substance.Therefore,alloying or substitution has been a feasible and common route utilized to enhance thermoelectric properties in these Zintl phase compounds,especially for YbZn0.4Cd1.6Sb2(ZT700 K=1.26),EuZn1.8Cd0.2Sb2(ZT650 K=1.06),and YbCd1.85Mn0.15Sb2(ZT650 K=1.14).     

Crystal Structures and Thermoelectric Properties of Sm-Filled Skutterudite Compounds Smy Fex Co4 - x Sb12

Polycrystalline samples of Sm partially filled skutterudites SmyFexCo4-xSb12 were prepared by melting and Spark Plasma Sintering technique. The results of Rietveld refinement showed that the obtained SmyFexCo4-xSb12 samples possessed filled skutterudite structures. The thermal parameter （B） of Sm is larger than that of Sb, Fe, and Co, indicating that Sm ＂rattled＂ in Sb-icosahedron voids. The effects of filling atom Sm on thermoelectric properties of these compounds were investigated. With the increase of Sm filling fraction （y）, electrical conductivity decreased, Seebeck coefficient increased and had a maximum value when y was 0.38; thermal conductivity reduced and had a minimum value when y was 0. 32. At 750 K, the highest figure of merit of 0.68 was obtained for Sm0.32Fe1.47Co2.53Sb12.     

Preparation and thermoelectric transport properties of Ba-, La- and Ag- doped Ca3Co4O9 oxide materials

The Ba-, La- and Ag-doped polycrystalline Ca2.9M0.1Co4O9 (M=Ca, Ba, La, Ag) thermoelectric bulk samples were prepared via citrate acid sol-gel synthesis method followed by spark plasma sintering technique. The bulk samples were characterized and analyzed with regard to their phase compositions, grain orientations as well as microstructures. The high temperature thermoelectric transport properties of the bulk samples were studied in detail. All bulk samples were found to be single-phased with modified body texture. The electrical resistivity was modulated as a result of carrier concentration modification, however the carrier transport process was not influenced; the Seebeck coefficient was deteriorated simultaneously. The total thermal conductivity was remarkably reduced, on account of the decreasing of phonon thermal conductivity. The thermoelectric properties of the Ba-, La-, and Ag-doped bulk samples were optimized, and the Ba-doped Ca2.9Ba0.1Co4O9 system was found to have the highest dimensionless figure of merit ZT0.20 at 973K, which was remarkably higher than that of the un-doped sample.     

Thermoelectric Properties of CexCo4Sb12 Prepared by MA-SPS

Starting with elementary powders, thermoelectric materials CexCo4Sb12 were prepared by mechanical alloying and spark plasma sintering (MA-SPS). XRD analyses reveal that the expected major phase, named skutterudite was formed in MA process and was kept after SPS. The thermoelectric properties of MA-SPS samples including resistivity, Seebeck coefficient, power factor, thermal conductivity and the dimensionless figure of merit (ZT) were studied by varying Ce content and temperature. Depending on Ce levels, both P and N types of thermoelectric semiconductors were obtained. MA-SPS sintered Ce1.0Co4Sb12 exhibits the highest ZT in the range of 100-500℃ and the maximum ZT is found at x=1.0 and 400℃.     

Thermoelectric properties of LaFe_3CoSb_(12) skutterudite materials with different nanostructures

Nanostructures with different morphologies could profoundly influence the electron and phonon transport in thermoelectric materials and thus their properties could be improved by tuning the nanostructures.The LaFe3CoSb12 skutterudite nano powders with differentmorphologies were fabricated via a hydro/solvo thermal route.The microstructures of the hot-pressed LaFe3CoSb12 bulks were characterizedthrough X-ray diffraction(XRD) and scanning electron microscopy(SEM) and the effects of the nanostructures on the thermoelectric properties were investigated by measuring the electrical conductivity,the Seebeck coefficient and the thermal conductivity.The results suggestedthat the mixed morphology of nanorods and nanospheres could enhance the electrical conductivity largely although the Seebeck coefficientwas decreased and the thermal conductivity was increased slightly.Differently,a higher Seebeck coefficient,a lower thermal conductivity anda lower electrical conductivity could be obtained for the LaFe3CoSb12 bulk with a single morphology of nanospheres.Consequently,the figure of merit of LaFe3CoSb12 bulk with a mixed morphology of nanorods and nanospheres could be increased by about 59% as compared tothat with a single morphology of nanospheres.     

Preparation and thermoelectric properties of ternary rare earth sulfide γ-Ce_(3–x)Eu_xS_4

The effect of Eu-substitution on the density and thermoelectric properties of ternary sulfide Ce3–xEuxS4 (0≤x≤0.8) compacts was investigated. Ce3–xEuxS4 powders were prepared via the sulfurization of the oxide using CS2 gas at 1473 K. The pressureless sintered Ce3–xEuxS4 compacts in the atmosphere were crystallized in the γ-phase. The density of the Ce3–xEuxS4 compacts increased with the increas-ing of Eu-substitution. Eu-substitution yielded a higher Seebeck coefficient and lower electrical resistivity. The highest value of the thermoe-lectric power factor of 1.41×10–4 W/K2m was obtained for the Ce2.2Eu0.8S4 compact at 673 K. It indicated that Eu-substitution was effective for improving thermoelectric properties of Ce3–xEuxS4.     

Effect of Y-filling on thermoelectric properties of CoSb3

The CoSb3 and Y0.18Co4Sb12 compounds were synthesized by a metallurgical route. Their bulk materials were prepared by the hot-pressed process under vacuum. Thermoelectric properties of the samples were measured by the thermoelectric measurement system and the laser flash diffusivity apparatus. The carrier type conversion of hot-pressed CoSb3 was found at about 530 K, while the conversion was missed for the Y0.18Co4Sb12 sample. Electrical conductivity of the Y0.18Co4Sb12 sample increased due to the increase of carrier concentration, and its thermal conductivity decreased due to the enhancement of phonon scattering. The value of ZT, figure of merit, for the Y0.18Co4Sb12 sample was obviously enhanced due to positive contribution of the electrical conductivity and the thermal conductivity.     

Zn4Sb3高性能热电材料的制备

A "reaction-extrusion process" has been developed to prepare Zn4Sb3 bulk materials with high thermoelectric performance.The synthesis,densification,and shape-forming of Zn4Sb3 bulk materials were realized simultaneously in one hot-extrusion process,and the resulting extrudates had high density with single β-Zn4Sb3 phase.A large extrusion ratio and a small punch speed are advantageous to enhance thermoelectric performance.The extruded Zn4Sb3 materials exhibited excellent thermoelectric performance,for example,the dimensionless thermoelectric figure of merit is 1.77 at 623 K,which is 36% higher compared to conventional hot-pressed materials.On the other hand,the incorporation of 1% SiC nanosized particles into Zn4Sb3 matrix leads to improvements in both thermoelectric and mechanical properties.     

HPHT synthesis and electrical transport properties of SmxCo4Sb12

Samarium-filled skutterudites SmxCo4Sb12(x=0.5,1.0) skutterudite thermoelectric(TE) materials with enhanced power factor were prepared by high-pressure and high-temperature(HPHT) technique.The microstructure properties were characterized with X-ray diffraction and scanning electron microscopy.The electrical resistivities and Seebeck coefficients of those samples were measured in the temperature range of 300-723 K,and the samples of SmxCo4Sb12 showed n-type conduction.The Seebeck coefficient in absolute valu...     

Electrical properties of new oxides （Ca0.85–xYxOH）1.16CoO2 synthesized by hydrothermal process

Layered cobalt oxides (Ca0.85-xYxOH)1.16CoO2 (x=0,0.05,0.1) were prepared by hydrothermal process and were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM).The electrical conductivity and Seebeck coefficient were measured from 323 to 573 K.The XRD and SEM analysis showed that all samples were single phase with plate-like morphology.The substitution of trivalent Y for divalent Ca had a remarkable effect on the enhancement of electrical properties.The maximum PF value,9.17×10-5 W/(m·K2),was obtained for (Ca0.75Y0.1OH)1.16CoO2 at 573 K,indicating that they are promising thermoelectric materials for middle-temperature usage.     

Transport properties of Zintl phase Yb1-xCaxCd2Sb2 at low temperature

We investigated the transport properties of isoelectronic substitution of Yb by Ca for Zintl phase YbCd2Sb2 below 300 K.The p-type Yb1-xCaxCd2Sb2(0.2≤x≤0.8) samples were synthesized via a solid-state reaction followed by suitable cooling,annealing,grinding,and spark plasma sintering(SPS) densification processes.For samples with x=0.2,0.4,0.5,0.6,0.8,the electrical conductivity,Seebeck coefficient,thermal conductivity,heat capacity and Hall effect measurements were carried out in the temperature range from 1...     

Synthesis and Study on Physical Properties for Magnetic Superconductor RESr2RuCu2O8（RE = Gd and Eu）

Single-phase magnetic superconductors RESrzRuCuzOs(RE = C,d and Eu) were successfully synthesized and investigations on their physical properties were carried out. It is found that the structure of the compounds is similar to that of YBa2Cu307 and its superconductivity coexists with weak ferromagnetic order in both compounds. The compounds exhibit magnetic order below TM = 130 and 136 K and superconducting below TC^onset = 35 and 46 K, respectively, for RE = Eu and Gd samples. There is slight difference in the magnetic properties between RE = Euand C,d compounds owing to various magnetic moments for C,d3 and Eu3 .     

Theoretical investigation on organolanthanide guanidinate complexes

Density functional theory (DFT) calculations were carried out on the compounds Cp2Ln-guan for Ln=Y, Lu, Yb, Dy and Gd, [guan=(iPrN)2CN(iPr)2]. The results were compared with the X-ray structures that were available from the literature; the calculations reproduced quite well the experimental structural features in these complexes exhibiting distorted tetrahedron geometry. The calculated evolution of the Ln-guan bond as a function of the cation showed that lanthanide-ligand distances increased with the increa...     

Effect of erbium substitution on thermoelectric properties of complex oxide Ca3Co2O6 at high temperatures

Polycrystalline particles of Ca3-xErxCo2O6 （x=0.0, 0.15, 0.3, 0.45 and 0.6） were synthesized using sol-gel method combined with Low Temperature Sintering procedure （LTS） to evaluate the effect of Er substitution on the thermoelectric properties of Ca3Co2O6. The crystal structure and microstructure were investigated using X-ray diffraction, infrared spectroscopy and scanning electron microscope. The electrical conductivity and Seebeck coefficient of the complex oxides were measured from 300 to 1073 K. The results showed that all the sampies were p-type semiconductors. The electrical conductivity increased with the increase in temperature. Er substitutions at Ca site affected carrier concentrations and carder mobility, resulting an increase in Seebeck coefficient and decrease in electrical conductivity. The power factor of Ca2.85Er0.15Co2O6 reached 10.66 μw/mK^2 at 1073 K.     

Optical Properties and Spectroscopic Parameters of Sm （DBM）3 Doped Polymethyl Methacrylate

Optical absorption spectra of Sm(DBM)3 doped PMMA (polymethyl methacrylate) in near infrared and visible region are presented. The energy levels were assigned and analyzed in terms of the free-ion Hamiltonian model. Energy levels and reduced matrix elements calculations were carried out using the complete 198 SLJ basis sets for the 4f^5 configuration. Judd-Ofelt parameters were evaluated and used to predict the radiative properties of the sample. The theoretical and experimental values for radiative lifetimes and branching ratios were discussed.     

Thermoelectric properties of Yb x Co_4 Sb_（12） system

Yb x Co 4 Sb 12 polycrystals were fabricated by vacuum melting combined with hot-press sintering.The effect of Yb-filling on thermoelectric property of unfilled skutterudite CoSb 3 was investigated,which indicated the enhancement of the power factor of the material.Transport properties of materials changed from semi-conductor to semi-metal during the measurement of electrical conductivity,which indicated the change of electronic band structure.The maximum value of electrical conductivity was about 190000 S/m at 300 K for all samples.On the basis of Yb-filling,power factor of Yb 0.2 Co 4 Sb 12 reached 5-6 mW/(m·K) during the measurement temperature.Thermal conductivity decreased with increase of Yb content,and the thermal conductivity of Yb 0.2 Co 4 Sb 12 reached 3.2 W/(m·K) at 600 K.The ZT value of Yb 0.2 Co 4 Sb 12 reached 1.16 at 700 K due to positive contribution from high power factor and low thermal conductivity.     

First principles study of structural,electronic, elastic and magnetic properties of cerium and praseodymium hydrogen system REH_x(RE:Ce,Pr and x=2, 3)

The structural, electronic, elastic and magnetic properties of cerium, praseodymium and their hydrides REH x(RE=Ce, Pr and x=2, 3) were investigated by the first principles calculations based on density functional theory using the Vienna ab-initio simulation package. At zero pressure all the hydrides were stable in the ferromagnetic state. The calculated lattice parameters were in good agreement with the experimental results. The bulk modulus decreased with the increase in the hydrogen content for these hydrides. The electronic structure revealed that di-hydrides were metallic whereas trihydrides were half metallic at zero pressure. A pressure-induced structural phase transition from cubic to hexagonal phase was predicted in these hydrides. The computed elastic constants indicated that these hydrides were mechanically stable at zero pressure. The calculated Debye temperature values were in good agreement with experimental and other theoretical results. A half metallic to metallic transition was also observed in REH3 under high pressure. Ferromagnetism was quenched in these hydrides at high pressures.     

How minor structural changes generate major consequences in photophysical properties of RE coordination compounds;resonance effect,LMCT state

Lanthanide coordination compounds of the formula Na[Ln(L)_4](1 Ln),where Ln=La~(3+),Eu~(3+),Gd~(3+),Tb~(3+),L=[L]~-and HL=dimethyl(4-methylphenylsulfo nyl)amidophosphate,were synthesized.Their structural and spectro scopic properties were discussed in detail based on X-ray diffraction measurements,IR spectroscopy,absorption and emission spectroscopy at 293 and 77 K and theoretical calculations of the intramolecular energy transfer(IET) rates.DFT calculations were used to investigate the 1 Ln electronic properties re quired to calculate the transition rates.30 and 22 pathways of intramolecular nonradiative energy transfer were examined in the case of 1 Eu and 1 Tb,respectively.It is shown that the main pathway for sensitization of the lanthanide emission is either the triplet(1 Eu) or singlet(1 Tb) transfer,occurring mainly through the exchange mechanism.The energy rates for energy transfer from S_1 and T_1 equal W_S=1.53 × 10~5 s~(-1)(1 Eu),W_T=5.14 × 10~6 s~(-1)(1 Eu) and W_S=4.09 × 10~7 s~(-1)(1 Tb),W_T=6.88 × 10~5 s~(-1)(1 Tb).The crucial role of the 7 F5 level in the energy transfer process of 1 Tb and the participation of the LMCT state in the depopulation of the ligand singlet state of 1 Eu were demonstrated.The influence of the resonance effect on the splitting of the~7 F_1 level in 1 Eu was analyzed.By comparing the properties of 1 Ln with the properties of 2 Ln coordination compounds,sharing the same ligand and crystallizing in the same crystallographic system(monoclinic),but with a different space group,it is demonstrated how slight structural changes can affect the photophysical properties of Ln compounds.