Shahed Rasekh

Shahed Rasekh
University of Aveiro | UA · CICECO - Centre for Research in Ceramics and Composite Materials

Ph. D.

About

90
Publications
11,187
Reads
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1,519
Citations
Introduction
Shahed Rasekh currently works as FCT Researcher at the CICECO, University of Aveiro. Shahed does research in Materials Engineering. Their current project is 'TOWARDS GREEN POWER GENERATION BASED ON HIGH TEMPERATURE THERMOELECTRIC MODULES'.
Additional affiliations
June 2019 - present
University of Aveiro
Position
  • Researcher
Description
  • Researcher Position, FCT (The Foundation for Science and Technology, Ministry of Science, Technology and Higher Education, Portugual). CICECO – formerly - Centre for Research in Ceramics and Composite Materials
May 2019 - May 2019
Max Planck Institute for Solid State Research
Position
  • Researcher
Description
  • Guest researcher financed by FCT post doctorate fellowship
November 2018 - December 2019
Max Planck Institute for Solid State Research
Position
  • Researcher
Description
  • Guest researcher financed by FCT Bilateral agreement

Publications

Publications (90)
Article
Full-text available
Ca3Co4-xNixO9 (x=0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. As a result of the Ni addition an increase in porosity has been detected. Moreover, the presence of Ni has been related with the increase of Ca2Co3O6 secondary phase and the appearance of a new NiO-CoO solid solutio...
Article
Full-text available
This work explores the effect of exposing the Bi2Ca2Co1.7Ox-textured ceramics at temperatures above working conditions, on mechanical and electrical properties. Microstructural studies have shown a first improvement of microstructure with an important grain growth, followed by the formation of porosity and the appearance of cracks for larger times....
Article
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Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical properties and the solubility, and impact of the substituting cation also depends largely on the preparation and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole tra...
Article
The main aim of this work was to estimate the dielectric constant of electrospun BaTiO 3 nanofibers (BT NF s) using theoretical models. The effect of calcination temperatures on morphology and crystal structure of BT NF s was also investigated by using SEM, TEM, XRD and Raman spectroscopy. The dielectric constant of BT NF s was calculated by applyi...
Article
Eco-benign and high-temperature-stable oxides are considered a promising alternative to traditional Bi2Te3, Bi2Se3 and PbTe-based thermoelectric materials. The quest for high performing thermoelectric oxides is still open and, among other challenges, includes the screening of various materials systems for potentially promising electrical and therma...
Article
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This paper reports a novel composite-based processing route for improving the electrical performance of Ca3Co4O9 thermoelectric (TE) ceramics. The approach involves the addition of metallic Co, acting as a pore filler on oxidation, and considers two simple sintering schemes. The (1-x)Ca3Co4O9/xCo composites (x = 0%, 3%, 6% and 9% vol.) have been pr...
Article
This work reports the microstructural and thermoelectric characterization of the misfit [Ca2CoO3-δ]0.62[CoO2] compound obtained by a solid-state synthesis using mollusk shells and a proteic sol-gel method, which uses gelatin as a polymerizing agent. The results clearly demonstrate the capability of these routes to produce pure Ca3Co4O9 with plate-l...
Article
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Zinc oxide (ZnO) has being recognised as a potentially interesting thermoelectric material, allowing flexible tuning of the electrical properties by donor doping. This work focuses on the assessment of tantalum doping effects on the relevant structural, microstructural, optical and thermoelectric properties of ZnO. Processing of the samples with a...
Article
This work explores the possibilities for a further enhancement of the thermoelectric properties of Ca3Co4O9 by Sr-doping combined with hot-pressing. Modified hot-pressing process resulted in highly-textured and dense ceramics. Sr-doping significantly improves electrical properties, resulting in extremely large power factor (1.2 mW/K²m at 800 °C) du...
Article
Full-text available
Bi2Sr2-xNaxCo2Oy thermoelectric materials with x = 0, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15 have been prepared by the classical solid state reaction. Microstructure has shown an important grain growth when Na is added, leading to very high bulk densities confirmed through density measurements. These modifications have produced a drastic decreas...
Article
Ca3Co4−xZrxOy polycrystalline ceramics with small Zr substitution have been prepared through the classical solid-state method. X-ray diffraction data have shown that all samples are composed only of Ca3Co4O9 and Ca3Co2O6 phases. Moreover, by increasing Zr substitution up to 0.07, Ca3Co2O6 phase content is decreased. Density measurements have reveal...
Article
Full-text available
Bi2AE2Co2Ox (AE=Ca, Sr, and Ba) thermoelectric compounds were grown from the melt by the laser floating zone technique. Microstructural analysis of as-grown samples has shown the formation of well-aligned thermoelectric grains together with a relative high amount of secondary phases. On the other hand, a short (24h) thermal treatment (810°C for Sr,...
Article
Bi2Sr2Co1.8Ox thermoelectric (TE) materials were prepared by three different synthesis methods producing nanosized precursors: coprecipitation (with ammonium carbonate or oxalic acid) and attrition milling, which were compared with those obtained by the classical solid state method. Microstructure has shown that precursors produced by coprecipitati...
Article
Full-text available
Bi1.6Pb0.4Ba2Co2Oy/3 wt% Ag composites have been textured using the laser floating zone technique. Microstructural observations have shown the formation of relatively high amounts of secondary phases and cracks along the plate-like grains in the as-grown materials. In spite of these microstructural features, electrical properties have not been dras...
Article
Bi2Ba2Co2Ox thermoelectric materials have been prepared through three different synthesis methods. The corresponding precursors were obtained from a coprecipitation method using oxalic acid, attrition milling, and classical solid state method (used as reference). Microstructural studies of precursors have shown that the ones produced by coprecipita...
Article
Full-text available
[Bi₂Ba₂O₄] p [CoO₂] thermoelectric ceramics have been successfully grown from the melt using the laser floating zone method, followed by a thermal treatment at 700 °C under air between 0 and 1532 h. The microstructural, thermoelectric, and mechanical properties were evaluated as a function of the thermal treatment length. Microstructure has shown t...
Article
Full-text available
Bi2Ca2Co1.7Ox thermoelectric ceramics were prepared by four different synthesis routes: coprecipitation with ammonium carbonate or oxalic acid, attrition milling, and solid state (as reference). Microstructure showed that coprecipitation and attrition milling produced sintered materials with less porosity and smaller particle sizes than the solid s...
Article
Full-text available
Bi2Ba2Co2Oδ thermoelectric ceramics with Ag additions (0, 1, 3, and 5 wt%) have been successfully textured using the laser floating zone method. Microstructure has shown that samples are composed by thermoelectric grains, together with a high amount of secondary phases, and that 3 wt% Ag addition leads to the best grain orientation. These microstru...
Article
Full-text available
Bi1.6Pb0.4Ba2Co2Oy thermoelectric ceramics with small Ag additions (0, 1, 3, and 5 wt%) have been textured using the laser floating zone method. Microstructure has shown a slight decrease on the secondary phases content and a better grain alignment in Ag added samples. These microstructural features are reflected in the thermoelectric properties, w...
Article
Full-text available
Bi2-xPbxBa2Co2Oy (x=0.0, 0.2, 0.4, and 0.6) misfit compounds were grown by the laser floating zone technique. Microstructural analysis has shown the formation of thermoelectric grains together with high amount of secondary phases. Thermoelectric grains orientation is increased until 0.4Pb, while further substitution drastically destroys the prefere...
Article
Full-text available
Bi2Ca2Co1.7Ox thermoelectric ceramics with small Ag additions (0, 1, 2, 3, 4, and 5 wt.%) have been successfully grown from the melt, using the laser floating zone method and subsequently annealed at 800 °C for 24 h. The microstructure has shown a reduction of the amount of secondary phases for Ag contents up to 4 wt.%. This microstructural evoluti...
Article
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A flexible, adaptable, economical and easily scalable processing route, allowing microstructural control, is presented. It involves classical solid state sintering method and addition of liquid promoting compound. Controlled porosity and high thermoelectric performance have been attained in Ca3Co4O9 by K2CO3 additions, drastically improving the sin...
Article
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Microstructure and superconducting properties of Bi2Sr2Ca1Cu2O8+δ +x wt% Ag (x=0 and 3) composite materials prepared by a sol-gel method and textured by a hot-pressing process have been investigated. Structural and microstructural studies have shown that Bi-2212/Ag composites exhibit better grain alignment, bigger grain sizes, and lower amount of s...
Article
Full-text available
Ca3Co4-xMnxOy polycrystalline thermoelectric ceramics with small amounts of Mn have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca3Co4O9 is the major phase, with small amounts of the Ca3Co2O6 one. Moreover, they show that the Mn has been incorporated into these two phases. Electrical resistivity decreas...
Article
Full-text available
Ca3Co4O9+x wt.% Ag (x=0, 1, 3, 5, and 10) polycrystalline thermoelectric ceramics have been prepared by a sol-gel route via nitrates followed by high temperature treatment before sintering. Out-of-plane XRD data have shown that major phase is the Ca3Co4O9 one, accompanied by metallic Ag. SEM observations have agreed with the XRD data. Apparent dens...
Article
Full-text available
Bi-2212 samples prepared by a solid-state reaction technique have been grown from the melt using the laser floating zone method. After annealing the as-grown bars, the samples showed a good grain alignment and a high transport critical current density. Secondary annealing processes were performed on the annealed samples with the aim of producing Bi...
Article
Full-text available
Bi2Sr2Co1.8Ox bulk polycrystalline ceramics were prepared by conventional sintering of powders, obtained by polymer solution method and by directional growth using the laser floating zone technique. Microstructural analysis showed randomly oriented grains in the classical sintered materials, while in the laser-textured samples well oriented crystal...
Article
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Ca3−xBaxCo4O9 bulk polycrystalline thermoelectric ceramics with x = 0.00, 0.01, 0.03 and 0.05 have been prepared through a classical solid state method. Microstructural characterizations of sintered samples have shown that Ba has been incorporated into the Ca3Co4O9 and/or Ca3Co2O6 structures and that no Ba-based secondary phases have been produced....
Article
Full-text available
The effect of environmental conditions on the microstructural, mechanical and thermoelectric properties of highly textured Bi2Ca2Co1.7Ox thermoelectric materials was investigated by powder X-ray diffraction, scanning electron microscopy, three point bending test, electrical resistivity, and thermopower measurements. Textured thin rods were directio...
Article
Full-text available
Ca3−xNaxCo4O9 polycrystalline thermoelectric ceramics with small amounts of Na (x=0, 0.01, 0.03, 0.05, 0.07, and 0.10) have been prepared using the classical solid state method. Microstructural characterization has shown that Na has been incorporated into the Ca3Co4O9 phase and that no Na-based secondary phases have been produced. It has also been...
Article
Full-text available
In this study, the effect of Yb-substitution on the structural, electrical and thermal transport properties of the Ca3Co4O9+δ system has been investigated at low temperature region (between 10 and 300 K). The resistivity of samples increases with increasing the Yb-concentration in the system. All the samples show a metal-semiconductor transition be...
Article
Full-text available
The efforts of carrying forward superconducting materials to commercialization can be overcome by materials with high performance potentiated by a suitable processing technique. In this work, extreme critical currents up to 241 A @ 77K were produced by tuning the crystal growth in a directional solidification process. Bulk rods of textured Bi-2212/...
Article
Full-text available
Three different synthesis methods producing nanometric grain sizes, coprecipitation with ammonium carbonate, oxalic acid, and by attrition milling have been studied to produce Ca3Co4O6 ceramics and compared with the classical solid state route. These three processes have produced high reactive precursors and all the organic material and CaCO3. have...
Article
Full-text available
Fe-substituted superconducting thin BiSrCaCuO rods with nominal compositions of Bi2Sr2Ca1Cu2−x Fe x O8+δ (x = 0, 0.01, 0.03, 0.05, and 0.1) were fabricated using the laser floating zone technique at two different growth speeds, 15 mm h−1 and 30 mm h−1. The influences of growth speed and Fe substitution on the grain alignment in the rods were evalua...
Article
Full-text available
Bi2−xPbxSr2CaCu2Oy textured materials (x = 0.0, 0.2, 0.4, and 0.6) have been successfully prepared by the laser floating zone technique. Microstructure and electrical properties (JC and TC) have been clearly affected by Pb addition. From the E–I curves, slope of the transition between the superconducting and the normal state (n) at 77 K reaches a m...
Article
Full-text available
Bi2 Ca2 Co1.7Ox bulk polycrystalline ceramics were prepared by the solid state method and by directional growth. Moreover, the effect of annealing on the textured materials has been studied. Microstructure has shown randomly oriented grains in the classical sintered materials while in the textured samples those were well oriented with their c-axi...
Article
Full-text available
Ca3Co4-xZnxOy (x = 0.01, 0.03, and 0.05) polycrystalline thermoelectric ceramics have been prepared by the classical solid state method. XRD data have shown that Ca3Co4O9 is the major phase, with small amounts of the Ca3Co2O6 one. Moreover, it has been found that the Zn has been incorporated into these two phases. Slight Zn doping decreases electri...
Article
Full-text available
Bi2Ca2Co1.7Ox nominal composition ceramic rods were textured by the electrically assisted laser floating zone technique. A new composite formed by three phases, two of them with well-known thermoelectric properties, Bi2Ca2Co1.7Ox and Ca3Co4O9, was obtained for the first time when the growth process was performed with a 300 mA applied current. Under...
Article
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Ca3-xRExCo4O9 thermoelectric ceramics with different rare earth (RE = Dy, Er, Gd, and Tb) substitution for Ca have been successfully produced by the classical solid state method. All these rare earths in small proportions produce the same effects on the thermoelectric phase, reflected on a similar and significant decrease of the electrical resistiv...
Article
Full-text available
Ca-3_xGaxCo4Oy), polycrystalline thermoelectric ceramics with small amounts of Ga have been synthesized by the classical solid state method. XRD data have shown that all the Ga has been incorporated into the Ca3Co4O9 and Ca3Co2O6 thermoelectric phases and no Ga-containing secondary phases have been produced. Moreover, for Ga contents >= 0.07, the C...
Article
Full-text available
Ca3-x,Mg-x,Co4O9, polycrystalline thermoelectric ceramics with small amounts of Mg have been synthesized by the classical solid state method. Microstructural characterizations have shown that all the Mg has been incorporated into the Ca3Co4O9 structure and no Mg-based secondary phases have been identified. Apparent density measurements have shown t...
Article
Full-text available
Bi2Sr2Co1.8Ox ceramics have been synthesized through solid-state reaction methods and directionally grown from the melt by laser floating zone technique. Mechanical and thermoelectric characteristics of this material were determined by three point bending tests and the four probe technique, respectively. The mechanical and thermoelectric properties...
Article
Full-text available
Ca3−xNdxCo4Oy polycrystalline thermoelectric ceramics with small amounts of Nd have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Nd has been incorporated into the Ca3Co4O9 and Ca3Co2O6 phases and no Nd-containing secondary phases have been produced. Apparent density measurements have revealed...
Article
Full-text available
Bi2−x Pbx Sr2CaCu2Oy (x = 0.0, 0.3, 0.4, and 0.5) textured materials have been prepared by the laser floating zone technique. The E − I curves showed and increase of the slope of the normal to superconducting transition with Pb addition. The best values have been obtained for the 0.4 Pb-doped samples, around 16 at 77 K. In spite of this improvement...
Article
Full-text available
Well-textured Bi2.02Sr2.02Ca0.98Cu1.99O x /2.9 wt % Ag composite samples have been grown by the laser floating zone at very low rates (1, 3, and 5 mm/h). The as-grown samples present superconducting behavior, as a result of being composed by long and well-textured Bi-2212 grains as major phase. After annealing, the samples do not dramatically incre...
Article
Full-text available
Ca3Co4−xTixO9 polycrystalline thermoelectric ceramics with small amounts of Ti have been prepared by the classical solid state method. X-ray diffraction data have shown that Ca3Co4O9 is the major phase, with small amounts of the Ca3Co2O6 one. Moreover, they show that Ti has been incorporated into these two phases. Electrical resistivity decreases,...
Article
Full-text available
Ca3-xSrxCo4O9 polycrystalline thermoelectric ceramics with small amounts of Sr have been synthesized by the classical solid state method. Microstructural characterizations have shown that all the Sr has been incorporated into the Ca3Co4O9 and Ca3Co2O6 structures and no Sr-based secondary phases have been produced. Apparent density measurements have...
Article
Full-text available
High-performance Ca3Co4O9 thermoelectric ceramic has been prepared from a Ca1−xCoxO/CayCo1−yO divorced eutectic structure produced by a directional melt-grown using the laser floating zone technique. This material has been grown at very high solidification rate in order to produce a very fine microstructure to reduce the necessary annealing time to...
Article
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Ca3Co4−xCrxO9 polycristalline thermoelectric ceramics with small amounts of Cr have been synthesized by the classical solid state method. Microstructural characterizations have shown that all the Cr has been incorporated into the Ca3Co4O9 structure and no Cr-containing secondary phases have been produced for Cr contents≤0.05. Apparent density measu...
Article
Full-text available
Ca3Co4−xCuxO9 polycrystalline thermoelectric ceramics with small amounts of Cu have been synthesized by the classical solid state method. X-ray diffraction data have shown that all the Cu has been incorporated into the Ca3Co4O9 structure and no Cu-containing secondary phases have been produced. Apparent density measurements have shown that all samp...
Article
Full-text available
Thermoelectric ceramics are based in a limited number of transition metal oxides (Co, Mn, Ni,…) which produce materials with high thermoelectric performances. Based on previously existing thermoelectric phases, the phase diagram equilibrium can help to design new thermoelectric ceramics based on other transition metals (for example, Fe). In this wo...