Fast preparation route to high-performances textured Sr-doped Ca 3 Co 4 O 9 thermoelectric materials through precursor powder modification

This work presents a short and very efficientmethod to produce high performance textured Ca3Co4O9thermoelectric materials through initial powders modifica-tion. Microstructure has shown good grain orientation, andlow porosity while slightly lower grain sizes were obtained insamples prepared from attrition milled powders. All samplesshow the high density of around 96% of the theoretical value.These similar characteristics are reflected in, approximately,the same electrical resistivity and Seebeck coefficient valuesfor both types of samples. However, in spite of similar powerfactor (PF) at low temperatures, it is slightly higher at hightemperature for the attrition milled samples. On the otherhand, the processing time reduction (from 38 to 2 h) whenusing attrition milled precursors, leads to lower mechanicalproperties in these samples. All these data clearly point out tothe similar characteristics of both kinds of samples, with adrastic processing time decrease when using attrition milledprecursors, which is of the main economic importance whenconsidering their industrial production

Microstructures and Thermoelectric Properties of Sintered Misfit-Layered Cobalt Oxide

Misfit-layered cobalt oxide Ca3Co4O9 is considered to be a prospective material for thermoelectric conversion. The thermoelectric properties are anisotropic owing to its anisotropic crystal structure. The crystal has preferred thermoelectric properties along the a-b plane. Therefore, the thermoelectric properties are improved and controlled by the degree of orientation of the sintered sample. In the present work, Sr-doped misfit cobalt oxide Ca2.7Sr0.3Co4O9 was prepared by solid-phase reaction, followed by uniaxial compression molding and sintering at 1173 K. The Seebeck coefficient α, electrical resistivity ρ, and dimensionless figure of merit ZT were measured as a function of the compression pressure applied in the uniaxial molding. α, ρ, and ZT as functions of the degree of orientation and the relative density are experimentally clarified and explained by calculations using the compound model

Granular and Lamellar Thermoelectric Oxides Consolidated by Spark Plasma Sintering

International audienceUsing the spark plasma sintering (SPS) technique, dense nanostructured Ca0.95Sm0.05MnO3 (n-type) and textured Ca3Co4O9 (p-type) ceramics were prepared. Nanoceramic powders of doped n-type were synthesized using two routes: coprecipitation and solid-state reaction. The SPS method has been used to control the samples’ densification and grain growth. Microstructural investigations reveal that the SPS technique results in high bulk density and homogeneous morphology for Ca0.95Sm0.05MnO3, and grain alignment for Ca3Co4O9. The thermoelectric and mechanical properties were investigated, showing a dependence on the starting grain size and being governed by the SPS conditions

Granular and Lamellar Thermoelectric Oxides Consolidated by Spark Plasma Sintering

International audienceUsing the spark plasma sintering (SPS) technique, dense nanostructured Ca0.95Sm0.05MnO3 (n-type) and textured Ca3Co4O9 (p-type) ceramics were prepared. Nanoceramic powders of doped n-type were synthesized using two routes: coprecipitation and solid-state reaction. The SPS method has been used to control the samples’ densification and grain growth. Microstructural investigations reveal that the SPS technique results in high bulk density and homogeneous morphology for Ca0.95Sm0.05MnO3, and grain alignment for Ca3Co4O9. The thermoelectric and mechanical properties were investigated, showing a dependence on the starting grain size and being governed by the SPS conditions

Thin-Wall Bulk High Temperature Superconductor as a Permanent Cryomagnet

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Thin-Wall Bulk High Temperature Superconductor as a Permanent Cryomagnet

International audienceThin-wall single domains with artificial patterned holes are highly interesting for stimulating superconducting and mechanical properties of bulk YBCO materials. YBCO single domains were successfully grown from multiple holes preforms by using TSIG or TSMG techniques. The thin-wall configuration enables a remarkable improvement in flux trapping and superconducting properties whatever the used growth process. Progressive oxygenation under high pressure associated to the large specific areas was shown to boost the material performances. A trapped field maximum of 0.84 T was recorded at 0.2 mm above the top surface of a 16 mm thin wall pellet at 77 K. Such complex geometry can be easily and abundantly produced by using an extrusion process. We report for the first time to our knowledge the growth of a single domain from an extruded preform. Thin-wall samples were then impregnated by resign/alloy for mechanical reinforcement

Extruded YBCO HTS Single Domain Bulk Materials for Permanent Magnets

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Ca3Co4O9 ceramics consolidated by SPS process: Optimisation of mechanical and thermoelectric properties

cited By 50International audienceCa3Co4O9 (349) thermoelectric (TE) oxide ceramics were successfully prepared by Spark Plasma Sintering process. The effects of the uniaxial pressure (30-100 MPa), the dwell temperature (700-900 °C) and the cooling rate were investigated. Microstructure analyses have revealed strong enhancements of the bulk density as the pressure level and the applied temperature during the SPS process are increased. Mechanical properties were investigated by using instrumented nanoindentation and three point bending tests. Hardness, elastic modulus, strength and fracture toughness were shown to improve drastically and depend on the processing parameters. Thermal expansion measurements reveal a noticeable anisotropy induced by unidirectional hot pressing. The mechanical, thermal and thermoelectric properties were correlated to the microstructure and crystallographic texture of the resulting ceramics. © 2010 Elsevier Ltd. All rights reserved