Andrei Kovalevsky

Andrei Kovalevsky
University of Aveiro | UA · Department of Materials and Ceramics Engineering

PhD

About

187
Publications
12,883
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4,942
Citations
Additional affiliations
February 2010 - present
University of Aveiro
February 2009 - January 2010
Flemish Institute for Technological Research
Position
  • Researcher

Publications

Publications (187)
Article
Driven by a need to develop low-cost and thermally stable materials for thermoelectric applications, donor-substituted strontium titanate is considered as a promising alternative to traditional thermoelectrics. The complex defect chemistry of SrTiO3-based materials imposes various limitations on identifying the relevant effects exerted on the elect...
Article
Inspired by recent research results that have demonstrated appealing thermoelectric performance of A-site cation-deficient titanates, this work focuses on detailed analysis of the changes in performance promoted by altering the defect chemistry mechanisms. The series of cation-stoichiometric SrTi1-xTaxO3±δ and A-site deficient Sr1-x/2Ti1-xTaxO3-δ c...
Article
Donor-substituted strontium titanate is known as one of the best highly performing n-type oxide thermoelectrics. In the present work, structural, microstructural, and thermoelectric properties of Sr1–xPrxTiO3±δ, Sr1–1.5xPrxTiO3±δ, and Sr1–yTi0.8Nb0.2O3±δ (x = 0.05–0.30, y = 0–0.10) perovskite-type titanates were assessed to identify the impact of n...
Article
The oxygen transport studies of dense Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3-δ (BSCF) ceramic membranes, prepared via glycine-nitrate route, demonstrated that the permeation rate is predominantly controlled by surface exchange kinetics when the membrane thickness is smaller than 1.00mm. In order to improve oxygen exchange, an asymmetric membrane concept inclu...
Article
This work focuses on designing highly-porous cellular NiAl2O4-based spinel ceramics through combined suspension emulsification/reactive sintering and further decoration of the pore surfaces by Ni nanoparticles for potential applications in heterogeneous catalysis. Due to kinetic limitations and specific porous structure, the reduction occurs withou...
Article
Full-text available
The perovskite-type calcium manganite exhibits interesting magnetic properties that can be tuned and enhanced by the laser floating zone (LFZ) method. This work explores, for the first time, the application of an external magnetic field during the LFZ growth of CaMn0.9Gd0.1O3. The effects of the field direction on structural, microstructural, elect...
Article
In continuation with the results explored in our recent previous study (https://doi.org/10.1016/j.apsusc.2021.150062), the current work sheds more light regarding the active in situ catalytic species in ceria additive loaded hydrogen storage system, MgH2. For this study, two samples, MgH2+0.167CeO2 and MgH2+0.5CeO2 were processed through mechanical...
Article
(Free download link until 10 July 2022: https://authors.elsevier.com/c/1f6W03PCJlLxkF ) *** Efficient use of barium-containing electrocatalysts for NOx decomposition in electrochemical solid oxide cells requires good chemical compatibility of these materials with the electrolyte in a temperature range 300–600 °C and imply the use of porous electrol...
Article
This work assesses the feasibility of processing CuFe1-xNixO2 (x=0, 0.02) using the Laser Floating Zone (LFZ) technique to grow fibres with different pulling rates, to tune their thermoelectric performance. Structural analysis showed CuFeO2 as the major phase. Formation of secondary phases is promoted by Ni addition, diminishing with decreasing pul...
Article
Full-text available
The alkaline electrolytic production of iron is gaining interest due to the absence of CO2 emissions and significantly lower electrical energy consumption when compared with traditional steelmaking. The possibility of using an iron-bearing pseudobrookite mineral, Fe2TiO5, is explored for the first time as an alternative feedstock for the electroche...
Article
Full-text available
MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides based on earth-abundant constituents, are prospective candidates for energy conversion applications, including photocatalysis. While the activity of individual MXenes towards various photocatalytic processes is still debatable, these materials were proved...
Article
Full-text available
Increasing Sr2+ concentration and the creation of A-site deficiency in La1-x-ySrxCoO3-δ (x = 0.3–0.7, y = 0–0.05) increase oxygen ionic conductivity, oxygen permeability of the dense ceramic membranes, and surface exchange limitations, in correlation with the oxygen nonstoichiometry variations. Regression analysis of the experimental data on oxygen...
Article
Liquid metals have emerged as potential materials for fuel cell and battery applications due to their suitable redox potentials, fast redox kinetics, and/or active participation in electrode reactions. In this work, we study the electrochemical oxidation behavior of antimony-lead melts by the use of a robust, yttrium-stabilized zirconia based, test...
Article
Full-text available
The electrochemical reduction of iron oxides in alkaline media arises as a novel approach for ironmaking and iron-rich waste valorisation. Strong advantages and attractive aspects of alkaline electroreduction include lower electric energy consumption, absence of CO2 emissions, and non-polluting valuable by-products such as H2 and O2. Another potent...
Article
Full-text available
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
In this work, brownmillerite-type calcium ferrite (Ca2Fe2O5) ceramics were prepared by two distinct routes, namely by a proteic sol-gel synthesis using commercial flavorless gelatin, and by a solid-state reaction method using mollusk shells. XRD analyses revealed single phase brownmillerite-type calcium ferrites in both cases. SEM-EDS analysis of s...
Article
Full-text available
This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components,...
Article
Full-text available
This work explores the possibilities for the processing of Ni- and Ti3C2Tx (T = OH, O) MXene-containing composite electrodes, by co-pressing and plastic deformation or by etching of the electrodes prepared directly by self-propagation high-temperature synthesis (SHS). Various material design approaches were also explored. In order to tune the Ti3C2...
Article
We present a study of magnetic and structural properties of La1−xGdxCoO3 compounds with x=0, 0.2, 0.5 and 1. The Gd term in magnetic susceptibility obeys the Curie–Weiss law with antiferromagnetic interaction between the magnetic moments of Gd3+ ions. The value of the paramagnetic Curie temperature Θ is proportional to Gd content and for GdCoO3 it...
Article
The stability and reproducibility of the electric properties in n-type doped ZnO represent known bottlenecks towards potential thermoelectric applications. The degradation is promoted by the vanishing of the electronic defects on oxidation and irreversible exsolution of the phase impurities. This work proposes a microstructural mechanism showing th...
Article
Porous 3 YTZ-Al2O3 membranes were processed aiming controlled cellular microstructures for potential separation and electrochemical applications. The processing method relies on emulsification of mixed suspensions of Al2O3 and 3 YTZ powders in sunflower oil. Taguchi experimental planning was used to seek guidelines for optimization of microstructur...
Article
The present work aims to evaluate relevant effects of the size of substituting rare-earth cation on electrical conductivity and thermal expansion of donor-doped SrTiO3 as ceramic components of electrochemical solid electrolyte cells. A series of strontium titanate-based ceramics with a moderate doping level and different cation stoichiometry, Sr0.9...
Article
For La1−x Prx CoO3 cobaltites with x = 0, 0.1, 0.2 and 0.3, the temperature dependence of magnetic susceptibility χ (T ) was studied in the temperature range from 5 to 400 K. Also the crystal structure of these cobaltites was investigated, and the effect of hydrostatic pressure up to 2 kbar on their susceptibility was measured at fixed temperatures...
Article
Full-text available
Electrochemical reduction of iron oxides into zero-valent iron (ZVI, Fe0) is a promising alternative to the traditional methods used for iron production. The electrochemical deposition of Fe0 from hematite and hematite-based Fe2−xAlxO3 ceramic in alkaline suspensions (10 M of NaOH) was assessed at relatively low temperature (90 °C). Ceramic composi...
Article
The present work reports the first attempt of thermoelectric module design, based on oxide materials grown through the laser floating zone technique. Two modules with 4-legs thermoelectric were assembled using Bi2Ba2Co2Oy fibres as p-type legs, while Ca0.9La0.1MnO3 and CaMn0.95Nb0.05O3 fibres were used as n-type legs. Structural and electrical char...
Article
The crystal structure, magnetic susceptibility as a function of temperature χ(T) in the range 5–400 K, and the hydrostatic pressure effect on χ at fixed temperatures T = 78, 150, and 300 K, were studied in perovskite-like compounds La1−xPrxCoO3 (x = 0, 0.1, 0.2, and 0.3). The obtained experimental data were analyzed using a two-level model with an...
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
Highly porous zirconia ceramics for prospective use as separators in alkaline electrolysis cells have been processed by emulsification of paraffin in concentrated zirconia suspensions. Effects of processing parameters on porosity, cell size distribution, and pore interconnectivity are studied through Taguchi statistical design. The porosity of zirc...
Article
The development of thermoelectrics for high-temperature applications imposes several essential requirements on the material properties. In some energy-conversion scenarios, the cost and thermal stability requirements may dominate over efficiency issues, making abundant, high-temperature-stable and low-toxic oxides attractive alternative thermoelect...
Article
The feasibility of recycling red mud waste by its direct transformation into highly-porous cellular ceramics was successfully demonstrated. Ceramic materials with designed cellular porosity were processed by emulsification of red mud suspensions with liquid paraffin. Taguchi method was used to study the effects provided by varying the red mud load...
Article
Full-text available
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
Full-text available
This work aims at the preparation of multifunctional titania-based photocatalysts with inherent capabilities for thermal co-activation and stabilisation of anatase polymorph, by designing the phase composition and microstructure of rutile-silicon carbide mixture. The processing involved a conventional solid state route, including partial pre-reduct...
Article
In this work, the laser floating zone technique (LFZ) of 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...
Article
CaMnO3–based materials represent a promising family of n-type oxide thermoelectrics. The objective of the present work is assessing the impacts on relevant structural, microstructural and thermoelectric properties of manganites when they are processed by the laser floating zone technique. For this purpose, donor-doped Ca0.9La0.1MnO3, CaMn0.95Nb0.05...
Article
Full-text available
Electrochemical reduction of low-conductive hematite-based ceramics represents a novel approach for iron recovery and waste valorisation. The process itself allows a flexible switching between hydrogen generation and iron reduction, important for the intermittent renewable-energy-powered electrolytic process. The present study focuses on the direct...
Presentation
Full-text available
Oxide-based thermoelectric materials are receiving a particular interest due to enhanced thermal and redox stability at high temperature, together with the absence of toxicity, and natural abundance of the constituent compounds. The objective of this work is to improve the thermoelectric performance of manganite-based oxide thermoelectrics processe...
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
Full-text available
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...
Presentation
Full-text available
Laser processing is known as one of the most versatile techniques to develop technological devices. The use of lasers constitutes nowadays an alternative methodology to the chemical routes for materials synthesis/growth. Bulk crystals, thin films and nanoparticles/nanostructures are currently achieved by laser processing techniques. The application...
Article
Full-text available
Oxide materials based on calcium manganite show clear prospects as thermoelectrics, provided by their stability at high temperatures and inherent flexibility in tuning the relevant electrical and thermal transport properties. Donor-doped CaMnO3 is an n-type semiconductor with a perovskite structure and relatively high thermoelectric performance. In...
Article
Polycrystalline Eu 1–x Ca x TiO 3–δ (0 ≤ x ≤ 1) samples were synthesised to investigate the interrelations among the crystal structure, local structural disorder, and thermoelectric properties. The Ca ²⁺ substitution is locally modifying (squeezing) the crystal structure, resulting in distinct differences between the long-range and local scales, e....
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
This work focuses on demonstration of reliable and versatile method for processing cellular mayenite (Ca12Al14O33) -based ceramics with designed porosity, with emphasis on potential catalytic applications. Highly porous (up to 82% of open porosity) monoliths were obtained by emulsification of liquid paraffin in aqueous suspensions of mixed CaCO3 an...
Article
This work aims to explore zirconium as a possible dopant to promote thermoelectric performance in bulk ZnO-based materials, both within the single-doping concept and on simultaneous co-doping with aluminum. At 1100–1223 K mixed-doped samples demonstrated around ∼2.3 times increase in ZT as compared to single-doped materials, reaching ∼0.12. The sim...
Poster
Full-text available
Today a particular interest is given to the oxide-based thermoelectric materials, due to enhanced thermal and redox stability, attractive properties at high temperature, the absence of toxicity, and natural abundance of the constituent compounds[1,2]. The objective of this work is to assess the possibilities for processing oxide thermoelectrics thr...
Article
Iron oxides are attractive for a variety of applications, since they offer unique physical and chemical properties, while being abundant and environmentally friendly. Some of those potential applications, including electrochemical and catalytic systems, require ceramics with designed porosity and well-developed percolation networks. In the present...
Chapter
Thermoelectric energy-conversion technology based on oxide materials offers promising advantages over “traditional” non-oxide and intermetallics systems due to higher stability of oxides at elevated temperatures and in various redox conditions, high natural abundance and favourable environmental issues. Oxides also possess a unique defect chemistry...
Article
Multimodal porous cellular alumina structures (monoliths) were prepared by an emulsion-gel casting technique using eco-friendly and inexpensive lipids such as corn oil, castor oil, margarine and their mixtures as the dispersed phase. The monoliths obtained showed good mechanical stability, exhibiting compressive strengths in the range of 8–50 N·mm⁻...
Article
Zinc oxide (ZnO) has a very broad and versatile range of applications provided by high abundance, optical and electrical properties, which can be further tuned by donor substitution. Al-doped ZnO is probably the most thoroughly investigated material regarding thermoelectric properties. Fairly reasonable electrical properties of donor-doped zinc oxi...
Article
The proton conductivity and solid solubility limits of acceptor strontium doped vanadium stabilised lanthanum niobate (SryLa1−yNb1-xVxO4-δ, x = 0.25, 0.30 and y = 0 to 0.10) were explored as potential proton conducting ceramic electrolytes. All samples were synthesized via a solid-state method. The phase purity, microstructure and thermal expansion...
Article
Magnetite (Fe3O4) offers unique physical and chemical properties, being an important material for many industrial applications. Certain limitations on the application conditions are, however, imposed by the redox stability issue. Fine control of the iron oxidation states represents a challenge for materials engineering. The present work explores re...
Article
Cellular Al2TiO5 and Al2TiO5 – Al2O3 composite ceramics were obtained by emulsification of liquid paraffin in aqueous suspensions of mixed TiO2 + Al2O3 powders, with subsequent burnout of the organic phase and 2-step reactive firing at high temperatures. The reactants ratio and paraffin to suspension volume ratio were used as primary parameters to...
Article
Full-text available
A series of Ba1-xEuxTiO3-δ (0.1 ≤ x ≤ 0.9) phases with ∼40 nm particle size were synthesized via a Pechini method followed by annealing and sintering under a reducing atmosphere. The effects of Eu(2+) substitution on the BaTiO3 crystal structure and the thermoelectric transport properties were systematically investigated. According to synchrotron X...
Article
This work proposes a new approach for electrochemical reduction of hematite to magnetite and/or metallic iron, based on ceramic cathodes with designed microstructures. The processing method, involving emulsification of concentrated aqueous ceramic suspensions with melted paraffin, enables preparation of cellular hematite ceramics possessing open po...
Article
One-dimensional Haldane gap materials, such as the rare earth barium chain nickelates, have received great interest due to their vibrant one-dimensional spin antiferromagnetic character and unique structure. Herein we report how these 1D structural features can also be highly beneficial for thermoelectric applications by analysis of the system CaxB...
Article
The interplay of unique cation arrangement and redox coupling in ferrospinels offers a wide range of magnetic and catalytic properties, evaluated mostly for low and intermediate temperature applications. This work focuses on high-temperature properties of magnesium-substituted magnetite, for prospective high temperature applications such as electro...
Chapter
The increasing concerns about global warming and its relation with greenhouse gas emission is opening a new opportunity for the development of alternative electric generators. In this context, thermoelectric generators, that are able to convert thermal energy directly from a temperature gradient into electrical energy, without any gas emission, can...
Article
This study highlights that Fe additive offers better catalytic properties than carbon, Fe-C (iron carbide/carbon composites) and Fe-Mg (Mg2FeH6) additives for the low temperature dehydrogenation of magnesium hydride. In-situ XRD study proves the formation of Mg2FeH6 phase in the iron additive loaded MgH2. Nonetheless, DSC study suggests that this M...
Article
Owing to their high stability and good bulk proton conductivity yttrium doped barium zirconate-based materials are considered as potential electrolytes for protonic ceramic fuel cell applications. Nonetheless, their refractory nature leads to problematic densification that can necessitate the addition of sintering additives. While these additives a...
Article
Full-text available
It has been reported that peak mixed conducting performance can only be obtained in doped ceria-based fluorite ceramics that contain cobalt sintering additives, when these materials are sintered below 1100 °C. Hence, this article provides a comparative analysis of the electrochemical behavior of such materials formed under the aforementioned condit...
Article
Driven by environmental challenges and global movement to carbon-lean technologies, the pyroelectrolysis process for iron extraction from oxide melts is being proposed as an interesting alternative to the traditional steelmaking. Still, one of the critical issues impacting the prospects of this technology includes the development of appropriate ano...
Article
This work explores the possibilities to design magnetite-based spinels through multiple simultaneous co-substitutions with transition metal cations, with emphasis on redox behavior and electronic transport. For the first time this approach was assessed for high-temperature applications, which is of particular interest for the development of consuma...
Article
Full-text available
In this study, hybrid microwave sintering of Ca3Co4O9 thermoelectric materials was implemented for the first time. Thermoelectric properties of samples sintered in different conditions and in conventional electrical furnace, using the same temperatures and dwell times, were assessed and compared. Microwave processing was found to promote densificat...
Article
A promising concept of consumable anode materials for high-temperature pyroelectrolysis process, which is expected to overcome the environmental and economical impacts of classical extractive metallurgy, relies on substituted magnetite-based ferrospinels, presenting high electrical conductivity, appropriate refractoriness, and redox stability. The...
Article
Magnesium aluminosilicates (MAS) represent a great importance for many electrical and catalytic applications. Recently, MAS-based glasses were considered as prospective for use as an electrolyte in steel making by molten oxide electrolysis process, an alternative electrometallurgical technique which offers prospects for environmental and economic a...
Article
This work focuses on assessing the feasibility of cathodic iron extraction from the magnetite based precursors. For this, electrochemical processes at Fe3O4/alkaline electrolyte interface were screened by cycling voltammetry. Based on these results, one obtained guidelines for selecting the conditions (i.e., potential and temperature) where efficie...