Satish Vitta
IIT Bombay, Metallurgical Engineering and Materials Science, Faculty Member
Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature... more
Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature application. In the present work, Al addition was found to be highly beneficial for improving the thermoelectric properties of Ag2Se. In Ag1.95Al0.05Se, a large enhancement in the charge carrier mobility (1127 cm2/V s) is witnessed due to the formation of Se-rich Ag2Se1.02 phase with improved grain connectivity through in situ formed AgAl phase. The synergetic effect of low carrier concentration and enhanced mobility in Al doped samples resulted in a high Seebeck coefficient and high electrical conductivity, leading to a high power factor of 3039 μW/m K2 at 300 K. The figure-of-merit of Ag1.95Al0.05Se was found to be 1.1 at 300 K i.e., 57% higher than for pure Ag2Se. The uni-leg device fabricated using Ag1.95Al0.05Se with electroplated Ni/Ag contacts showed a conversion efficiency of ∼3.2% for a temperature difference of 93 K, i.e., comparable to the best reported value for conventional bismuth telluride.
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The combined structural and dielectric response of langasite, Ba3NbFe3Si2O14 shows unique temperature and frequency dependence, attributed to presence of distributed potential wells.
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High temperature superconducting films of YBa{sub 2}Cu{sub 3}O(7-x) YBCO were grown on SrTiO{sub 3}, LaA1O{sub 3}, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and... more
High temperature superconducting films of YBa{sub 2}Cu{sub 3}O(7-x) YBCO were grown on SrTiO{sub 3}, LaA1O{sub 3}, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.
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Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature... more
Mixed ion–electron conductor Ag2Se is an n-type semiconductor owing to the intrinsic Se vacancies. By reducing Se vacancies, Ag2Se has been demonstrated as a potential environment-friendly thermoelectric material for near room temperature application. In the present work, Al addition was found to be highly beneficial for improving the thermoelectric properties of Ag2Se. In Ag1.95Al0.05Se, a large enhancement in the charge carrier mobility (1127 cm2/V s) is witnessed due to the formation of Se-rich Ag2Se1.02 phase with improved grain connectivity through in situ formed AgAl phase. The synergetic effect of low carrier concentration and enhanced mobility in Al doped samples resulted in a high Seebeck coefficient and high electrical conductivity, leading to a high power factor of 3039 μW/m K2 at 300 K. The figure-of-merit of Ag1.95Al0.05Se was found to be 1.1 at 300 K i.e., 57% higher than for pure Ag2Se. The uni-leg device fabricated using Ag1.95Al0.05Se with electroplated Ni/Ag contacts showed a conversion efficiency of ∼3.2% for a temperature difference of 93 K, i.e., comparable to the best reported value for conventional bismuth telluride.
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The combined structural and dielectric response of langasite, Ba3NbFe3Si2O14 shows unique temperature and frequency dependence, attributed to presence of distributed potential wells.
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High temperature superconducting films of YBa{sub 2}Cu{sub 3}O(7-x) YBCO were grown on SrTiO{sub 3}, LaA1O{sub 3}, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and... more
High temperature superconducting films of YBa{sub 2}Cu{sub 3}O(7-x) YBCO were grown on SrTiO{sub 3}, LaA1O{sub 3}, and YSZ substrates using two techniques: excimer laser ablation with in situ annealing and co-evaporation of Y, Cu, and BaF2 with ex-situ annealing. Film thicknesses were typically 5000 A, with predominant c-axis alignment perpendicular to the substrate. Critical temperatures up to Tc(R=O)=90 K were achieved by both techniques. Ellipsometric measurements were taken in the range 1.6 to 4.3 eV using a variable angle spectroscopic ellipsometer. The complex dielectric function of the laser ablated films was reproducible from run to run, and was found to be within 10 percent of that previously reported for (001) oriented single crystals. A dielectric overlayer was observed in these films, with an index of refraction of approximately 1.55 and nearly zero absorption. For the laser ablated films the optical properties were essentially independent of substrate material. The magnitude of the dielectric function obtained for the co-evaported films was much lower than the value reported for single crystals, and was sample dependent.
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Amount of waste heat exergy generated globally ~ 69.058 EJ can be divided into, low temperature < 373 K, 30.496 EJ, medium temperature 373 K – 573 K, 14.431 EJ and high temperature > 573 K, 24.131 EJ. The minimum number of... more
Amount of waste heat exergy generated globally ~ 69.058 EJ can be divided into, low temperature < 373 K, 30.496 EJ, medium temperature 373 K – 573 K, 14.431 EJ and high temperature > 573 K, 24.131 EJ. The minimum number of thermoelectric pn-junctions required to convert this high temperature exergy into electrical power using currently known best materials is found to increase from 8.22x1011 to 24.66x1011 when the aspect ratio of the legs increases from 0.5 cm− 1 to 1.5 cm− 1. To convert the low temperature exergy, 81.76x1011 to 245.25x1011 junctions will be required. The amount of alloys required to synthesize these is of the order of ‘millions of tons’ which means the elements, Bi, Te, Pb, Sb, Sn and Se required is also of similar magnitude. The current production of these elements however falls far short of this requirement by several orders of magnitude, indicating significant materials supply chain risk. The production of these elements and devices, even if resources are ...
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The relaxation of diamagnetic magnetization in the c-axis-aligned YBa2Cu3O(7-x) thin film is studied as a function of orientation and temperature in the range of 5-50 K at H = 0.2 T. The magnetization M(T,H) in the orientations H parallel... more
The relaxation of diamagnetic magnetization in the c-axis-aligned YBa2Cu3O(7-x) thin film is studied as a function of orientation and temperature in the range of 5-50 K at H = 0.2 T. The magnetization M(T,H) in the orientations H parallel to c and H perpendicular to c and at all the ...
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Research Interests: Engineering, Magnetic Materials, Nanofabrication, Nanocomposites, Permanent Magnets, and 12 morePhysical sciences, Magnetic Properties, Composite Material, Nickel, Curie temperature, Grain Boundary, Magnetoresistance, Ferromagnetic Materials, Ferrites, Space Groups, Coercive Force, and Noise Measurement
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Zinc arachidate (ZnA) LB multilayers have been exposed to H 2 S to form ZnS nanoclusters within the layered matrix of arachidic acid (AA). The as-deposited ZnA multilayer consists of arachidate molecules packed in a hexagonal layer cell,... more
Zinc arachidate (ZnA) LB multilayers have been exposed to H 2 S to form ZnS nanoclusters within the layered matrix of arachidic acid (AA). The as-deposited ZnA multilayer consists of arachidate molecules packed in a hexagonal layer cell, with the alkyl chain tilted at about 32° away ...
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Materials Science and Engineering, A133 ( 1991 ) 799-802 799 Solidification of Fe40Ni40B20 at high undercooling Satish Vitta*, CS Proctor, RF Cochrane and AL Greer University of Cambridge, Department of Materials Science and Metallurgy,... more
Materials Science and Engineering, A133 ( 1991 ) 799-802 799 Solidification of Fe40Ni40B20 at high undercooling Satish Vitta*, CS Proctor, RF Cochrane and AL Greer University of Cambridge, Department of Materials Science and Metallurgy, Pembroke Street, ...
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The structure of NiNb/C multilayers as a function of annealing at 200 and 320 °C has been studied. The layered structure is found to be extremely stable even after annealing at 320 °C. The interdiffused layer present at the two... more
The structure of NiNb/C multilayers as a function of annealing at 200 and 320 °C has been studied. The layered structure is found to be extremely stable even after annealing at 320 °C. The interdiffused layer present at the two interfaces and before annealing undergoes ...
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A Nd-YAG laser giving 5 ns, 266 nm pulses was used to melt and subsequently quench thin, pure metallic films on a liquid Al/Al,O, substrate at 10'-10'2 K s - '. Transmission electron microscopy together with electron... more
A Nd-YAG laser giving 5 ns, 266 nm pulses was used to melt and subsequently quench thin, pure metallic films on a liquid Al/Al,O, substrate at 10'-10'2 K s - '. Transmission electron microscopy together with electron diffraction was used to study the competitive nucleation and growth ...
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The phenomenon of electromigration (EM) has been extensively studied in metals and alloys of Al, Au, and Cu because of their usage in semiconductor integrated cir-cuits.' The study of EM in oxide materials had not been possible... more
The phenomenon of electromigration (EM) has been extensively studied in metals and alloys of Al, Au, and Cu because of their usage in semiconductor integrated cir-cuits.' The study of EM in oxide materials had not been possible earlier because of their poor electrical ...
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Ceramic–metal (MgO combined with Fe, Ti and Ni 80Nb 20) and polymer–metal (polycarbonate combined with Ag and Pd) nanocomposite multilayers were deposited at room temperature by laser ablation (at 248 nm). The multilayers were... more
Ceramic–metal (MgO combined with Fe, Ti and Ni 80Nb 20) and polymer–metal (polycarbonate combined with Ag and Pd) nanocomposite multilayers were deposited at room temperature by laser ablation (at 248 nm). The multilayers were characterized by X-ray reflectometry, infrared spectroscopy and transmission electron microscopy. In the case of MgO/metal multilayers, well-layered structures are produced down to layer periodicities of 1.2 nm, necessary