Structure and magnetocaloric properties of La1-xKxMnO3 manganites

A technology of obtaining the single-phase ceramic samples of La1-xKxMnO3 manganites and the dependence of their structural parameters on the content of potassium has been described. Magnetocaloric effect (MCE) in the obtained samples has been measured by two independent methods: by classical direct methodic and by a method of magnetic field modulation. The values of MCE obtained by both methods have been substantially differed. The explanation of the observed divergences is given. The correlation between the level of doping and MCE value has been defined. The value of TC determined by the MCE maximum has been conformed to the literature data received by other methods.Comment: 14 pages, 6 figures, 3 table

W-2 wt.%Y2O3 composite: Microstructure and mechanical properties

A W-2Y(2)O(3) composite is produced by powder metallurgy, including the pressing of the mixed elemental powders, their sintering and hot forging. The microstructure of the obtained composite is investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. It appears that the material is composed of W grains having a mean size of 1-2 mu m and Y2O3 particles having a mean size of 300 nm to 1 mu m. The W grains contain a high density of dislocations. The mechanical properties of this material are investigated using nanoindentation and 3-point bend test. Berkovich hardness value is found to be 4.9 GPa at 10 N load, which is similar to that of pure W. 3-Point bend test shows that the composite starts to show ductile behavior approximately at 400 degrees C and the bending stress continuously decreases from 200 degrees C to 1000 degrees C. (C) 2012 Elsevier B.V. All rights reserved

Interfacial thermoelectric and mechanical properties of indigenously prepared Ni–Cr–Cu/Co4Sb12 skutterudite thermoelectric joints

Thermoelectric and mechanical properties of indigenously prepared Ni–Cr–Cu/Co4Sb12 skutterudite thermoelectric joints are reported. Co4Sb12 based skutterudite compounds are highly enticing mid-temperature thermoelectric materials for waste-heat harvesting. Ni–Cr–Cu electrode powder is prepared by ball milling, and a one-step sintering route is adopted to fabricate the Ni–Cr–Cu electrode/n-type Dy0.4Co3.2Ni0.8Sb12 thermoelectric joints. The processed Ni–Cr–Cu/skutterudite joint interface is continuous without having any crack and has low contact resistance (<12 μΩ cm2). The contact resistance at the interface of the joints decreases to 7 μΩ cm2 under thermal ageing at 823 K for 15 days in a vacuum. The mechanical properties of the joints are not degraded even after ageing at 823 K for 15 days. The theoretical lifetime of the skutterudite device using the Ni–Cr–Cu/Dy0.4Co3.2 Ni0.8Sb12 joints is calculated to be 11 years while maintaining the hot side temperature of the device at 773 K. Our results demonstrate that indigenously prepared Ni–Cr–Cu/Co4Sb12 thermoelectric joints can be effectively used for skutterudite module fabrication

Magneto-transport studies in yttrium doped lanthanum manganites between 10-300K

443-447<span style="font-size: 16.0pt;mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">The hole doped manganite systems A1-xAxMnO3 (where A represents lanthanides and A's are divalent cations) with x<span style="font-size: 13.5pt;mso-bidi-font-size:6.5pt;font-family:" times="" new="" roman","serif";="" mso-fareast-font-family:hiddenhorzocr"="">≤<span style="font-size:13.5pt; mso-bidi-font-size:6.5pt;font-family:HiddenHorzOCR;mso-hansi-font-family:" times="" new="" roman";="" mso-bidi-font-family:hiddenhorzocr"=""> <span style="font-size:16.0pt; mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">0.45 exhibit the electronic transport behavior that results from the complex interplay  among charge carriers, spin and lattice. The system shows a metal-insulator transition and the transition temperature (TMI) is strongly dependent on various factors, viz, dopant, thermal history, oxygen content grain size etc. Large magneto-resistance observed <span style="font-size: 16.0pt;mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">near TMI in these perovskites is another interesting feature that has enormous implications in device and sensor technology. In the present paper, we report our results on the temperature dependence of the electrical resistivity on a set of samples of the type La<span style="font-size:12.5pt;mso-bidi-font-size:5.5pt; font-family:" arial","sans-serif""="">0.6<span style="font-size:16.0pt; mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">Y0.07Ca0.33MnO3, prepared by a new pyrophoric technique. Our analysis confirms <span style="font-size: 16.0pt;mso-bidi-font-size:9.0pt;font-family:" times="" new="" roman","serif""="">adiabatic small polaron hopping forT> T<span style="font-size:12.0pt; mso-bidi-font-size:5.0pt;font-family:" times="" new="" roman","serif""="">MI while, in the metallic region (T <span style="font-size:12.0pt; mso-bidi-font-size:5.0pt;font-family:" times="" new="" roman","serif""="">M1), electron-electron and electronmagnon scattering play the dominant role in defining the influence of annealing time on <span style="font-size:16.5pt;mso-bidi-font-size: 9.5pt;font-family:" times="" new="" roman","serif""="">the electrical resistivity of fine grained polycrystalline La<span style="font-size:12.5pt; mso-bidi-font-size:5.5pt;font-family:" arial","sans-serif""="">0.6Y0.07Ca0.33MnO3 pellets. </span

Comparison of microstructure in Ni-Al single splats and millimeter sized drops

Splat studies are a central area of research because they can provide fundamental knowledge on the phenomena controlling the final coating properties such as coating microstructure and adhesion. Wetting and heat transfer are expected to influence the final splat shape while they are in turn controlled by the presence of oxides and adsorbed species on the substrate surface. It is however difficult to follow the flattening of a sprayed droplet at the micrometer scale. Since the mid nineties, so-called free falling experiments have been developed with which it is possible to simulate the thermal spray process. The millimetre sized drops allow investigating the flattening and solidification occurring in milliseconds instead of in microseconds.In this study, the microstructure of plasma sprayed Ni-Al splats and millimetre sized droplets produced on TiAlV and pure Ti substrates, respectively, are compared. By use of scanning electron microscopy (SEM), especially the cross-section of splats and droplets has been investigated. In the splats, diffusion across the splat-substrate interface and the formation of an interface layer is detected. In the droplets, up to 3 different layers are formed at the interface to the substrate. The microstructure at the interface and the phases present are discussed and their influence on heat transfer and coating properties are described.In this study, the microstructure of plasma sprayed Ni-Al splats and millimetre sized droplets produced on TiAlV and pure Ti substrates, respectively, are compared. By use of scanning electron microscopy (SEM), especially the cross-section of splats and droplets has been investigated. In the splats, diffusion across the splat-substrate interface and the formation of an interface layer is detected. In the droplets, up to 3 different layers are formed at the interface to the substrate. The microstructure at the interface and the phases present are discussed and their influence on heat transfer and coating properties are described

Investigation of microstructure and microhardness of pure W and W-2Y(2)O(3) materials before and after ion-irradiation

Pure W and W-2Y(2)O(3) materials were fabricated using powder metallurgy method. The microstructures of the materials were investigated by electron back-scattered diffraction and transmission electron microscopy techniques. Both materials contain 1-2 mu m size W grains. In the case of W-2Y(2)O(3), the material contains yttria particles having sizes between 300 and 900 nm. The W matrix in W-2Y(2)O(3) shows stronger texture than that of pure W. Berkovich hardness values are 4.5 GPa in pure W and 4.9 GPa in W-2Y(2)O(3) for a 10 N load. Ion irradiation experiments were performed on both materials at the JANNuS facility (Saclay, France) using Fe and He ions with energies of 24 MeV and 2 MeV, respectively. Radiation loops are present on the W grains whereas on yttria particles, radiation-induced damages appear as voids. Berkovich hardness values of irradiated materials are slightly higher than the non-irradiated materials. Results of the microstructure and microhardness of irradiated as well as non-irradiated materials are presented in detail. (C) 2014 Elsevier Ltd. All rights reserved