Enhanced thermoelectric performance in spark plasma textured bulk n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3

Bulk p and n-type bismuth tellurides were prepared using spark plasma texturization method. The texture development along the uniaxial load in the 001 direction is confirmed from both x-ray diffraction analysis and electron backscattering diffraction measurements. Interestingly, those textured samples outperform the samples prepared by conventional spark plasma sintering (SPS) leading to a reduced thermal conductivity in the ab-plane. The textured samples of n-type BiTe2.7Se0.3 and p-type Bi0.5Sb 1.5Te3 showed a 42% and 33% enhancement in figure of merit at room temperature, respectively, as compared to their SPS counterparts, opening the route for applications. © 2013 AIP Publishing LLC

A facile liquid foam based synthesis of nickel nanoparticles and their subsequent conversion to Ni<SUB>core</SUB>Ag<SUB>shell</SUB> particles: structural characterization and investigation of magnetic properties

A facile route for the synthesis of nickel nanoparticles in stable aqueous foams is reported. The Ni nanoparticles were roughly 12-15 nm in size and were stable as aqueous suspensions or powders when oleic acid was used as a capping agent. These Ni nanoparticles were subsequently coated with a silver shell in view of the extra stability and the enhanced manipulative ability afforded by the silver nanocoating. This was accomplished by a simple transmetallation reaction wherein the nanoparticle surface nickel atoms act as localized reducing agents for the silver ions in solution. As the silver shell is formed through the surface reaction a reduction in the average size of the Nicore occurs. After the core-shell structure formation, the Nicore has an average diameter of 10-20 nm while the Agshell has a thickness of 2-4 nm. The pristine oleic acid coated Ni and NicoreAgshell nanoparticles were probed for their magnetic characteristics by a vibrating sample magnetometer. The nascent, oleic acid coated Ni nanoparticles display a low superparamagnetic blocking temperature, TB, of 20 K. The field dependent magnetic behaviour above and below TB displays the standard features corresponding to superparamagnetism, as expected for very small Ni crystallites suggesting again that each 12 nm particle is polycrystalline. The magnetic contribution in the NicoreAgshell system comes from only the Ni core and predictably, the blocking temperature of this system is below 12 K due to the smaller size of the Ni core

Erratum: “Enhanced thermoelectric performance in spark plasma textured bulk n -type Bi 2 Te 2.7 Se 0.3 and p-type Bi 0.5 Sb 1.5 Te 3 ” [Appl. Phys. Lett. 102, 211901 (2013)]

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Erratum: “Enhanced thermoelectric performance in spark plasma textured bulk n -type Bi 2 Te 2.7 Se 0.3 and p-type Bi 0.5 Sb 1.5 Te 3 ” [Appl. Phys. Lett. 102, 211901 (2013)]

International audienceIn the article entitled “Enhanced thermoelectric performance in spark plasma textured bulk n-type Bi2Te2.7Se0.3 and p-type Bi0.5Sb1.5Te3,”1 the composition of the n-type compound was erroneous and should be read as “Bi2Te2.7Se0.3” instead of BiTe2.7Se0.3. These typos do not affect the conclusions of this work. The authors are grateful to M. Quentin Lognoné and Dr. Franck Gascoin for pointing out the error in the original article

La0.7Ca0.3MnO3 / Mn3O4 composites: does an insulating secondary phase always enhance the low field magnetoresistance of manganites?

Composites of magnetoresistive La0.7Ca0.3MnO3 (LCMO) with insulating Mn3O4 are useful as a model system because no foreign cation is introduced in the LCMO phase by interdiffusion during the heat treatment. Here we report the magnetotransport properties as a function of sintering temperature Tsinter for a fixed LCMO/Mn3O4 ratio. Decreasing Tsinter from 1250°C to 800°C causes an increase in low field magnetoresistance (LFMR) that correlates with the decrease in crystallite size (CS) of the LCMO phase. When plotting LFMR at (77 K, 0.5 T) vs. 1/CS, we find that the data for the LCMO/Mn3O4 composites sintered between 800°C and 1250°C follow the same trend line as data from the literature for pure LCMO samples with crystallite size > ~25 nm. This differs from the LFMR enhancement observed by many authors in the "usual" manganite composites, i.e., composites where the insulating phase contains cations other than La, Ca or Mn. This difference suggests that diffusion of foreign cations into the grain boundary region is a necessary ingredient for the enhanced LFMR.D09/0

Comparative studies on the structure and magnetic properties of Ni–Zn ferrite powders prepared by glycine-nitrate auto-combustion process and solid state reaction method

Ni–Zn ferrite compositions (Ni1−xZnxFe2O4) are well known due to their remarkable soft magnetic properties, which potentially have a broad range of applications in many areas. In this study, Ni–Zn ferrite with the chemical formula of Ni0.64Zn0.36Fe2O4 was prepared by the glycine-nitrate autocombustion process (GNP) and solid state reaction method (SSRM). In order to achieve a desirable particle size, the SSRM powders were milled for 3 h at a milling rate of 200 rpm. The structure and magnetic properties of the ferrite powders, which were synthesized by both methods, were characterized and their properties were compared. The results indicate that a significant amount (∼ 90 wt.%) of nanocrystalline Ni0.64Zn0.36Fe2O4 ferrite with the average crystallite size of 47 nm, particle size of 200 nm, saturation magnetization of 73 emu/g and coercivity of 54 Oe has been formed by means of the glycine-nitrate process. The results also show that not only the saturation magnetization of the GNP ferrite powder is relatively similar to that of the milled SSRM powders, but also it is synthesized at a much shorter duration than that of the solid state reaction method