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.     

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.     

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.     

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.     

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...     

Crystal structure,thermal expansion and electrical conductivity of Pr（Ga1-xCox）0.9Mg0.1O3-δ （x=0, 0.1, 0.2, 0.3）

Pr（Ga1-xCox）0.9Mg0.1O3-δ （x=0, 0.1, 0.2, 0.3） was synthesized using solid-state reaction technique to study the effects of Co doping on their structure and properties. Room and high temperature XRD, DSC and electrical conductivity measurement with D.C. four-probe technique were adopted in the study. The results indicated its orthorhombic-distorted perovskite structure at room temperature. PrGa0.9Mg0.1O3-δ maintained its orthorhombic-distorted structure between 298 and 1173 K. For Pr（Ga0.7Co0.3）0.9Mg0.1O3-δ, such structure existed below 873 K. From 873 to 1173 K, it possessed tetragonal structure. The transformation from orthorhombic to tetragonal structure at 873 K was of second order. The intrinsic volume thermal expansion of tetragonal structured Pr（Ga0.7Co0.3）0.9Mg0.1O3-δ Was about 50% higher than those of PrGa0.9Mg0.1O3-δ. The electrical conductivity increased with Co content. The activation energies of conduction for Pr（Ga1-xCox）0.9Mg0.1O3-δ are in range from 0.197 to 0.246 eV, much lower than 1.543 eV for PrGaO3.     

Crystal structure, thermal expansion and electrical conductivity of Pr(Ga1-xCox)0.9Mg0.1O3-δ(x=0,0.1,0.2,0.3)

Pr(Ga1-xCox)0.9Mg0.1O3-δ(x=0, 0.1, 0.2, 0.3) was synthesized using solid-state reaction technique to study the effects of Co doping on their structure and properties. Room and high temperature XRD, DSC and electrical conductivity measurement with D.C. four-probe technique were adopted in the study. The results indicated its orthorhombic-distorted perovskite structure at room temperature. PrGa0.9Mg0.1O3-δ maintained its orthorhombic-distorted structure between 298 and 1173 K. For Pr(Ga0.7Co0.3)0.9Mg0.1O3-δ, such structure existed below 873 K. From 873 to 1173 K, it possessed tetragonal structure. The transformation from orthorhombic to tetragonal structure at 873 K was of second order. The intrinsic volume thermal expansion of tetragonal structured Pr(Ga0.7Co0.3) 0.9Mg0.1O3-δ was about 50% higher than those of PrGa0.9Mg0.1O3-δ. The electrical conductivity increased with Co content. The activation energies of conduction for Pr(Ga1-xCox)0.9Mg0.1O3-δ are in range from 0.197 to 0.246 eV, much lower than 1.543 eV for PrGaO3.     

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.     

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℃.     

Structure and Electrical Conductivity of Compositely Doped Oxide Solid Electrolyte La0.8Sr0.2Ga0.8Mg0.12Co0.08O2.8

(La, Sr) (Ga, Mg) O3-δ, (LSGM) perovskite compositions doped with transition metal Co on the B-site were prepared by solid state reaction. The effect of partial substitution of Ga for Co, La0.8Sr0.2Ga0.8Mg0.12Co0.08O2.8 (LSGMC2008) on the electrical conductivity was discussed. The results showed the compacted samples sintered at 1350℃ possesses increased electrical conductivity at low temperatures. The XRD patterns of the title materials indicated that LSGMC2008 possessed orthorhombic perovskite-type structure. The grains distributed relatively uniform from SEM photo. The Arrhenius plots of ionic conductivity in air of the LSGMC2008 exhibited differing slopes in the low-and high-temperature regions, and the corresponding Ea values were much lower than that of LSGM2020. All of these suggested that even at low sintering temperature, proper amount Co doped was beneficial to improve ionic conductivity of LSGM.     

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.     

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).     

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...     

Synthesis and sintering of samarium rich SmS_x and its electrical property

Non-stoichiometric samarium monosulfide(SmS_x, 0.55≤x≤1.2) was synthesized from Sm_2S_3 and SmH_3 at 1273 K for 3 h under vacuum. The influence of reaction ratio of Sm_2S_3 to SmH_3 on the fabrication of SmS_x was investigated. The fabrication of SmS required the molar ratio of Sm_2S_3 to SmH_3 above 1. Lattice parameter of synthetic SmS_x increased firstly and then decreased to saturate following with the addition of SmH_3 content. SmS_x compact was sintered at 1373 K by spark plasma sintering. Density of synthetic SmS_x was about 99% of theory density. Seebeck coefficient of n-type semiconductor Sm Sx decreased as temperature rose. The absolute value was distributed between 170–280 μV/K. The electrical resistivity of SmS_x(0.86≤x≤1.07) decreased with temperature increasing and showed similar temperature dependence. The surplus Sm which randomly distributed in the SmS_x(0.55≤x≤0.75) matrix led to a remarked reduction of electrical resistivity. The optimized power factor for SmS_(0.6) and Sm S_(0.75) could reach 1500 μW/(K~2·m) at 600 K.     

Preparation and performance of Pr-doped Ba_(0.5)Sr_(0.5)Co_(0.8)Fe_(0.2)O_(3-δ) cathode for IT-SOFCs

(Ba0.5Sr0.5)1-xPrxCo0.8Fe0.2O3-δ(BSPCFx;x=0.00-0.30) oxides were synthesized by a sol-gel thermolysis process using combination of PVA and urea,and were also investigated as cathode material for intermediate temperature solid oxide fuel cells(IT-SOFCs).X-ray diffraction(XRD) results showed that all the samples formed a single phase cubic pervoskite-type structure after being calcined at 950 oC for 5 h and the lattice constant decreased with the Pr content increasing.The electrical conductivity of Ba0.5Sr0.5Co0.8Fe0.2O3-δ(BSCF) was greatly enhanced by Pr-doping.The thermal expansion coefficient(TEC) of BSPCFx was increased with the content of Pr increasing,and all the thermal expansion curves had an inflection at about 250-400 oC due to the thermal-induced lattice oxygen loss and the reaction of Co and Fe ion.Ac impedance analysis indicated that BSPCFx possessed better electrochemical performance.The polarization resistance of the sample with x=0.2 was only ～0.948 Ω cm2 at 500 oC,significantly lower than that of BSCF(～2.488 Ω cm2).     

Nanocrystalline La2Mo2O9 and Its Characterization

In this work, both the thermal expansion and electrical conductivity of nanocrystalline La2Mo2O9 were studied.The nanocrystalline powder of La2Mo2O9 was obtained by sol-gel method, and with the help of SHP (superhigh pressure)up to 4.5 × 104 atm at 700 ℃ for a short time, and the nanocrystalline powder was densified without obvious particle size growth. The electrical conductivity of nanocrystalline La2Mo2O9 was one orderof magnitude lower than that of the microcrystalline sample at the same temperature. Owing to the phase transition, the microcrystalline La2Mo2O9 has an abrupt increase of thermal expansion with a peak value of 48 × 10-6 K-1 at 556 ℃. For the nanocrystalline material, the peak value increases to 112 × 10-6 K-1 at 520 ℃. On the other hand, above 600 ℃ the significant growth of particle size of the nanocrystalline La2Mo2O9 was observed, accompanying by a tremendous increase of thermal expansion with a peak value of third higher than that of La2Mo2O9.     

Fabrication and Characterization of SOFC Anode, Ni-SDC Cermet

NiO and Ce0.8Sm0.2O1.9 were synthesized by the combination of sol gel and citric acid-nitrate low temperature self-propagating combustion method. Anode precursors which include home-made NiO and Ce0.8Sm0.2O1.9 were prepared by different NiO content and fabrication condition. The anode precursors with pure hydrogen at 820 ℃ for 2.5 h were reduced, The electrical conductivity was tested, and the effect of microstructure on electrical conductivity of Ce0.8Sm0.2O1.9 composite anodes was investigated. The results show that the anode electrical conductivity depends strongly on the anode microstructure that is dramatically affected by Ni content and fabrication condition.     

Upconversion luminescence ofNaYF4：Yb,Er nanocrystals with high uniformity

The NaYF4：Yb,Er nanocrystals were synthesized via the thermal decomposition ot metal oleate precursors, lhe nanocrys- tals in hexagonal structure were highly uniform and in size of 25 nm. The bright upconversion luminescence was observed under the excitation of 980 nm laser and the upeonversion emission spectra were investigated at different pump powers. The emission intensity ratio of red light to green light linearly increased with pump power increasing. This result indicated that there existed a large threshold power of saturation pump for the first excitation state in NaYFa：Yb,Er nanocrystals comparing to that in bulk material.     

Growth and spectral characteristics of a new promising stoichiometric laser crystal: Ca9Yb（VO4）7

A Ca9Yb(VO4)7 crystal with dimensions of Φ23 mm×35 mm was grown successfully by Czochralski method. Its thermal conductivity was 1.06 W/(m?K) at room temperature. The absorption cross-sections at 980 nm were 1.80×10–20 cm2 and 1.28×10–20 cm2 for π- and σ- polarizations, respectively, with a full-width at half-maximum of 34 nm. The crystal had a broad emission at around 1025 nm with a full-width at half-maximum of 67 nm for π- polarization and 70 nm for σ- polarization. The emission cross-sections of the crystal were calculated by using reciprocity method and Füchtbauer-Ladenburg formula. The emission cross-sections at 1025 nm were 3.57×10–20 cm–2 and 1.91×10–20 cm–2 for π- and σ- polarization, respectively. The fluorescence lifetime was 332 μs. The results indicated that the crystal is a promising femtosecond and tunable laser material.