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MnFe2O4-based spinels by mechanochemical and thermochemical reaction of siderit...
Antunes, I.; Ruivo, L. C. M.; Tarelho, L. A. C.; Yaremchenko, A. A.; Kovalevsky, A. V.; Frade, J. R.The manganese ferrite has been processed by mechanosynthesis, using reactive siderite and MnO2 powder mixtures, with and without subsequent heat treatment. Taguchi planning was used to assess the impact of milling conditions (rotational speed and time) and subsequent calcination temperature on conversion of precursors, based on integrated intensities of the main XRD peaks of precursor phases FeCO3 (104) and MnO...
Effects of laser floating zone processing on electrical and magnetic properties...
Ferreira, N. M.; Carreira, F.; Kovalevsky, A. V.; Costa, F. M.; Valente, M. A.Manganites present fascinating physical properties which can be tuned according with the method and processing conditions. In this work, Ca1-xPrxMnO3 (x = 0.03, 0.06, 0.1) materials were prepared by the Laser Floating Zone technique (LFZ), under different pulling rates (25 to 100 mm/h) in air and argon atmospheres, obtaining fibres with 2.5 mm diameter. Such processing conditions promote the formation of second...
Laser processing as a tool for designing donor-substituted calcium manganite-ba...
Carreira, F. P.; Ferreira, N. M.; Kovalevsky, A. V.In this work, the laser floating zone technique (LFZ) for donor-substituted calcium manganite-based thermoelectrics were assessed using Ca1-xPrxMnO3 (x = 0.03, 0.06, 0.1) as a model system. Fibres were grown by LFZ with pulling rates of 25, 100 and 200 mm h−1 in various atmospheres (air, vacuum and argon). Strongly non-equilibrium conditions imposed by LFZ promoted the formation of impurities in (Ca, Pr)MnO3 ce...
Oxide thermoelectrics prepared by laser melting: effects of processing atmosphere
Lopes, D.; Ferreira, N. M.; Carreira, F. P.; Fortes, Iolanda; Kovalevsky, A. V.Thermoelectric materials can convert waste heat into electrical energy, thus contributing to the sustainable energy technologies. Traditional thermoelectric materials, despite their good performance, suffer from two main problems, the toxicity/scarcity of the elements used and their stability in harsher work conditions like high temperatures or non-inert atmospheres. Thermoelectric oxides appear to be a promisi...
Oxide thermoelectrics prepared by laser melting: effects of processing atmosphere
Lopes, D.; Ferreira, N. M.; Carreira, F. P.; Fortes, Iolanda; Kovalevsky, A. V.Traditional thermoelectric materials suffer from two main problems, the toxicity/scarcity of the elements used and their stability at high temperatures or in non-inert atmospheres. Thermoelectric oxides appear to be a promising alternative to traditional materials due to natural abundance of the constituents and high thermal stability. This work focuses on the processing of these materials using the Laser Float...
Thermoelectric modules built using ceramic legs grown by laser floating zone
Ferreira, N. M.; Lopes, D.; Kovalevsky, A. V.; Costa, F. M.; Sotelo, A.; Madre, M. A.; Rezania, A.The present work reports thefirst attempt of thermoelectric module design, based on oxide materials grownthrough the laserfloating zone technique. Two modules with 4-legs thermoelectric were assembled usingBi2Ba2Co2Oyfibres as p-type legs, while Ca0.9La0.1MnO3and CaMn0.95Nb0.05O3fibres were used as n-type legs.Structural and electrical characterisation of the individualfibres was performed, and the results comp...
Selected approaches for designing oxide thermoelectrics
Kovalevsky, A. V.Thermoelectric (TE) effect provides an elegant solution for conversion of the waste heat into electrical energy, based on the intrinsically simple technology employing no moving parts and possessing self-sufficiency to enable mobile or remote applications. In some energy-conversion scenarios the cost and thermal stability requirements may dominate over effciency issues, making abundant, high-temperature-stable ...
Ceramic-based thermoelectric materials processed by laser
Ferreira, N. M.; Madre, M. A.; Sotelo, A.; Kovalevsky, A. V.; Costa, F. M.Today a particular interest is given to the oxide-based thermoelectric materials, due to enhanced thermal and redox stability, attractive properties at high temperature, together with the absence of toxicity, and natural abundance of the constituent compounds. The objective of this work is to assess the possibilities for processing oxide thermoelectrics through laser floating zone (LFZ) method, including identi...
High-temperature thermoelectric energy harvesting: materials and approaches
Kovalevsky, A. V.Thermoelectric (TE) technology allows direct production of electrical energy from waste heat and natural heat sources. Although today thermoelectrics are hardly competitive with heat engines at large scale, absence of moving parts, inherent simplicity and scalability of this solid-state technology enable various applications in automotive/aerospace sector, in harsh and remote environments and for solar energy c...
Specific approaches towards design of the thermoelectric oxides
Kovalevsky, A. V.Sustainable energy supply to the population based on environmentally friendly and efficient technologies represents one of the major societal challenges in 21st century. One of the solutions is thermoelectric conversion of waste heat or solar heat into electricity, using sustainable and scalable devices, with self-sufficiency to enable mobile or remote applications. This talk will feature some promising strateg...