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.     

DFT studies of thermoelectric properties of R–Au intermetallics at 300 K

Thermoelectric and electronic properties of cubic bi-intermetallics R-Au(R = Tb, Ho. Er. Tm and Yb)compounds were explored. Electronic properties i.e. density of states and band structure were computed using first principles calculations which proved the metallic nature of these compounds. Post-DFT(BoltzTraP) calculations were carried out to explore their thermoelectric properties like electrical conductivities. Seebeck coefficient, electronic thermal conductivities and figure of merit. The highest Seebeck coefficient and figure of merit were found for YbAu among these compounds which are 105 μV/K and 0.285 respectively. All the calculations were carried out at 300 K. Large values of figure of merit obtained for these compounds at room temperature indicate that these materials can be used for thermoelectric devices however need experimental verification.     

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.     

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℃.     

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...     

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.     

Synthesis of nanostructured spherical aluminum oxide powders by plasma engineering

Irregularly shaped aluminum oxide particles were plasma atomized resulting in narrow size range distribution of spherical nanostructured powders. Cooling rates, on the order of 10⁶ to 10⁸ K/s, were obtained from the different quenching medias, viz. air, water, and liquid nitrogen. Plasma-engineered powder particles developed nanosize crystallites, while solidification provided insight into the morphological feasibility in refinement of grain size. X-ray diffraction (XRD) methods have been used to quantify the crystallite size obtained with different quenching media. Raman peak shift validated the X-ray analysis in anticipating the grain refinement with increasing cooling rates. Salient structural morphology characteristics and a detailed understanding of spheroidized plasma-sprayed alumina powders were analyzed through scanning electron microscopy (SEM) studies. Formation of nanograins, novel metastable phases, and amorphous structure were endorsed by transmission electron microscopy (TEM) investigations.     

镀钨碳纳米管增强铜基复合材料的制备及性能

采用羰基热分解法对多壁碳纳米管表面进行镀钨处理,并以镀钨碳纳米管和电解铜粉为原料,进行机械球磨混粉和放电等离子体烧结,制备了镀钨碳纳米管/铜基复合材料.采用场发射扫描电镜观察了粉体和复合材料的组织形貌,并对复合材料物相进行了X射线衍射分析.探讨了镀钨碳纳米管含量和放电等离子体烧结温度对复合材料致密度、抗拉强度、延伸率和电导率的影响.结果表明,镀钨碳纳米管质量分数为1%和烧结温度为850℃时,复合材料的致密度、抗拉强度和电导率最高.与烧结纯铜相比,复合材料的抗拉强度提高了103.6%,电导率仅降低15.9%.     

水热法和氢气还原法制备纳米Mo–40Cu复合粉末及其烧结性能研究

结合水热法和氢气还原法制备纳米Mo–40Cu复合粉末,利用X射线衍射仪、扫描电子显微镜、透射电镜等手段研究了氢气气氛下烧结工艺对Mo–40Cu复合材料组织和力学性能的影响。结果表明,最佳制粉工艺为水热温度400 ℃和氢气还原温度700 ℃,获得了均匀的Mo–40Cu复合粉末,粉末粒径为70~90 nm;在氢气气氛下最佳烧结工艺为1300 ℃保温2 h,合金的相对密度、抗弯强度、硬度、电导率和热导率分别为98.1%、1060 MPa、HRA 51、20.8 MS·m-1和191.7 W·m-1·K-1,热膨胀系数在500~700 ℃约为10.8×10-6 K-1,合金中组织均匀,晶粒细小,尺寸约为3~4 μm。     

Synthesis and characterization of tungsten and barium co-doped La_2Mo_2O_9 by sol-gel process for solid oxide fuel cells

Herein, we demonstrate the synthesis of W and Ba co-doped La_2Mo_2O_9(LBMWO) nanocrystalline powder by a sol-gel process. In all the compositions have general formulae La_(1.9)Ba_(0.1)Mo_(2-x)W_xO_(8.95)(x = 0-0.40). The crystal structure, microstructure and conductivity of LBMWO were characterized by X-ray diffraction, scanning electron microscopy and electrical impedance spectroscopy. In addition, the thermal and decomposition properties of the LBMWO gel were analyzed by differential scanning calorimetry-thermogravimetric. The results reveal that all LBMWO powders calcined at 700 ℃ have a cubic structure;the average crystallite size is about 48 nm. The unit cell parameter of LBMWO powders increases with increase in W content. The as-synthesized nanocrystalline LBMWO samples exhibit excellent sinterability and a relatively lower sintering temperature of 900 ℃. A high relative density of -96% is achieved after sintering at 900 ℃ which is in good agreeme nt with the re sults of the SEM. Moreover, W and Ba codoping suppresses the phase transition and effectively stabilizes the β-phase at low temperature. At the same time,La_(1.9)Ba_(0.1)Mo_(1.85)W_(0.15)O_(8.95) exhibits high ionic conductivity, 3.07 x 10~(-2) S/cm at 800 ℃. It is therefore concluded that co-doping can improve the properties of La_2MO_2O_9 electrolytes.     

Influence of milling media on the structure and agglomeration behaviour of some hardmetal powder

This paper presents the influence of milling media on the structure and morphology of WC–Co powders for sintered tools. WC–Co powders have been milled in two different organic media, acetone and isohexane. The characterisation of the as-milled samples has been done by X-ray diffraction, scanning electron microscopy (SEM) and differential scanning calorimetry. The mean crystallite size decreases with milling time for the samples processed in acetone, while in the case of isohexane, the crystallite size stays at a relatively constant value when increasing the milling duration. The calculated mean crystallite size is below 50?nm for any milling duration, with larger values for acetone (16–46 nm) as compared to isohexane samples (10–12 nm). The SEM revealed that the dried powder is composed of agglomerated submicronic particles, and at high magnification, the presence of nanoparticles is noticed. The density of the aggregates was linked to the polarity of the solvents, which influences the sedimentation kinetics.     

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.     

Structural,Optical and Impedance Studies of Hydrothermally and Solvothermally Prepared SnO<Subscript>2</Subscript> Nanocrystallites for Conducting Electrode Application

Nanocrystalline SnO₂ powders were synthesized by hydrolysis and solvolysis of SnCl₂ followed by a fast nucleation process in Teflon lined autoclave. The as prepared samples were calcined at 400 ^°C for 4 h to attain stable phase. The X-ray diffraction pattern confirms tetragonal crystal structure for both hydrothermally and solvothermally prepared nanoparticles and the average crystallite size is calculated to be 14 and 30 nm respectively. Williamson–Hall plot (W–H plot) reveals low value of strain induced broadening using uniform deformation model. Absorption co-efficient of prepared SnO₂ was determined using UV–Visible absorption spectrum. Nyquist plane plot shows the decreased electrical resistance of SnO₂ with increasing the applied potential resulting in increased conductivity. The increasing conducting behavior of tin oxide nanoparticles can be used as conducting layer in photoelectrodes.     

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...     

Thermoelectric properties of Sr0.9La0.1TiO3 and Sr2.7La0.3Ti2O7 with 15%Ag addition

15%Ag-added cubic perovskites Sr0.9La0.1TiO3 and Ruddlesden-Popper （RP） phases Sr2.7La0.3Ti2O7 were fabricated via hydrothermal synthesis, cold pressing and high-temperature sintering. The structure and thermoelectric properties were also investi-gated for all samples. The results indicated that Ag precipitated as a second phase. Ag addition made electrical conductivity and ab-solute Seebeck coefficient enhanced, as a result, the ZT values were enhanced both for two series. Compared with cubic perovskite, RP phase was subjected to smaller impact by Ag addition. The reasons for enhancing ZT value and the different impact for two series by Ag addition were also discussed.     

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.     

Thermoelectric properties of quaternary chalcogenide Cu2ZnSnS4 synthesised by mechanical alloying

ABSTRACT

The quaternary chalcogenide Cu₂ZnSnS₄ has emerged as a potential thermoelectric (TE) material due to its low thermal conductivity (κ), high Seebeck coefficient (S) and composition including earth-abundant, low-cost and non-toxic elements. In this work, Cu₂ZnSnS₄ was synthesised from a mixture of Cu, Zn, Sn and S powders using a mechanical alloying method. As a result, Cu₂ZnSnS₄ powders were formed after 16?h of milling, without additional heat treatment. After milling, the powders were heat-treated at 723?K for 24?h and then sintered by spark plasma sintering under an applied pressure of 60?MPa at 873?K for 10?min. The heat-treated Cu₂ZnSnS₄ sample showed a wide-band-gap of 1.49?eV. The sintered Cu₂ZnSnS₄ sample exhibited S and κ values of 170 μV K^?1 and 1.06 W m^?1 K^?1, respectively with an electrical conductivity σ of 1240 S m^?1 and a dimensionless figure of merit (ZT) of 0.022 at 663?K.     

Preparation and characterization of Ce_(0.8)La_(0.2–x)Y_xO_(1.9) as electrolyte for solid oxide fuel cells

In this study, ultrafine Ce0.8La0.2–x Y x O1.9（for x=0, 0.05, 0.10, 0.15, 0.20） powders were successfully prepared by the sol-gel method.The samples were characterized by fourier transform infrared（FTIR）, thermogravimetric and differential scanning calorimetry（TG-DSC）, X-ray diffraction（XRD）, scanning electron microscopy（SEM）, AC impedance and thermal expansion measurements.Experimental results indicated that highly phase-pure cubic fluorite electrolyte Ce0.8La0.2–x Y x O1.9 powders were obtained after calcining at 600 °C.The as-synthesized powders exhibited high sintering activity, the Ce0.8La0.2–x Y x O1.9 series electrolytes which have higher relative densities over 96% could be obtained after sintered at 1400 °C for 4 h.Ce0.8La0.15Y0.05O1.9 electrolyte sintered at 1400 °C for 4 h exhibited higher oxide ionic conductivity（σ800 oC=0.057 S/cm）, lower electrical activation energy（E a=0.87 e V） and moderate thermal expansion coefficient（TEC=15.5×10-6 K-1, temperature range 25–800 °C）.     

Volume Fraction of Graphene Platelets in Copper-Graphene Composites

Copper-graphene composite films were deposited on copper foil using electrochemical deposition. Four electrolyte solutions that each consist of 250 mL of graphene oxide suspension in distilled water and increasing volume of 0.2 M solution of CuSO₄ in steps of 250 mL were used to deposit the composite films with and without a magnetic stirrer. Graphene oxide in the films was reduced to graphene by hydrogen treatment for 6 hours at 673 K (400 °C). The samples were characterized by X-ray diffraction for identification of phases, scanning electron microscopy for distribution of graphene, energy dispersive spectrometry for evaluation of elemental composition, electrical resistivity and temperature coefficient of electrical resistance and thermal conductivity. Effective mean field analysis (EMA) was used to determine the volume fraction and electrical conductivity of graphene and interfacial thermal conductance between graphene and copper. The electrical resistivity was reduced from 2.031 to 1.966 ???? cm and the thermal conductivity was improved from 3.8 to 5.0 W/cm K upon addition of graphene platelets to electrolytic copper. The use of stirrer during deposition of the films increased the average size and the thickness of the graphene platelets and as a result the improvement in electrical conductivity was lower compared to the values obtained without the stirrer. Using the EMA, the volume fraction of graphene platelets that was responsible for the improvement in the electrical conductivity was found to be lower than that for the improvement in the thermal conductivity. The results of the analysis are used to determine the volume fraction of the thinner and the thicker graphene platelets in the composite films.