M. A. Madre

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• Ph. D.
• Professor (Full) at University of Zaragoza

Sr-doped Ca3Co4O9 p-type, and Ce-doped CaMnO3 n-type compounds were prepared through the solid-state method. XRD patterns showed that both samples are nearly single phase, with very small amounts of secondary phases. SEM observation indicated that p-type compound is composed by plate-like grains, with some degree of porosity, while n-type compound...

The global energy crisis demands innovative solutions to recover wasted heat from industrial processes, especially in energy-intensive sectors like ceramics, glass, and automotive manufacturing. Thermoelectric power generation, which directly converts heat into electricity using solid-state devices, has emerged as a promising approach for enhancing...

This study explores the effect of single doping with different rare earth elements (Y, La, and Yb) on the structural, morphological and electrical properties of CaMnO3 bulk ceramics, aiming to improve their thermoelectric performance. Ca(1‐x)RxMnO3 (R = Y, La, Yb; x = 0, 0.05, 0.10) samples were synthesized via a solid‐state reaction. XRD analysis...

Abstract This study investigates the fabrication and performance of ceramic-based thermoelectric modules for high-temperature energy conversion, based on Ca2.93Sr0.07Co4O9 and Ca0.91Y0.03La0.03Yb0.03MnO3 p- and n-type materials. The p-type materials were prepared through attrition milling and classical sintering, while ball milling and hot uniaxial...

A classical ceramic route has been used in this work to prepare Y and La co-doped CaMnO3 thermoelectric compound seeking to improve its thermoelectric properties. The study highlights significant improvements in electrical and thermal transport properties achieved with minimal doping levels and a cost-effective synthesis process. The co-doping stra...

This work presents a comparative analysis of pure and Ag-intercalated Ca3Co4O9 multilayer thermoelectric materials prepared through the hot-uniaxial pressing technique. Samples were prepared by attrition milling and hotpressed at 900 °C and 55 MPa for 1 h. They were mirror polished, and some of them were stacked with and without intermediate Ag foi...

Bi1.6Pb0.4Sr2Co2O8 samples have been textured by the Laser Floating Zone (LFZ) process using Nd:YAG, and CO2 laser radiation. Using different wavelengths resulted in significant structural and microstructural modifications. Powder XRD patterns showed that the thermoelectric phase is the major one in both cases. Microstructural studies revealed that...

A-, and B-site multiple-doped Ca0.97Y0.01La0.01Yb0.01Mn1–2xNbxMoxO3 was studied for improving its thermoelectric thermoelectric performance. Samples were prepared from planetary milled precursors and sintered at 1310ºC for 12 h. XRD showed that sintered samples are nearly single phase, with small amounts of CaMn2O4. SEM analysis revealed that grain...

In the present work, the effect of different annealing-time on the properties of Bi2Sr2Ca1Cu1.75Na0.25Oy (Bi-2212) superconducting compound is presented. First, the samples were produced by hot-pressing method under 33 MPa pressure at 750 °C in accordance with previous works. After annealing, the samples were kept at 840 °C for 15, 30 and 60 h, res...

Bi2Ca2Co2 − xCuxOy + 4 wt%Ag (with x between 0 and 0.20) thermoelectric materials were prepared through a sol-gel method via nitrates. Powder XRD patterns showed the presence of thermoelectric phase as the major one, accompanied by metallic silver. SEM observations identified three different secondary phases in the samples, together with an exagger...

Attrition-milling process has been applied to Ce-doped CaMnO3 precursors to obtain small grain-size powders. The use of Ce4+ as dopant instead a Rare Earth3+ has allowed decreasing by 50% the atomic proportion of dopant, to obtain equivalent charge carrier concentration, which is required for attaining promising properties for thermoelectric applic...

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....

The effect of K substitution for Ca in Bi 2 Ca 2-x K x Co 2 O y (x= 0.0, 0.05,0.075, 0.10, and 0.125) thermoelectric ceramics, produced via laser floating zone (LFZ) method, have been systematically investigated. XRD patterns are quite similar for all samples and main peaks in the patterns correspond to reflection planes of the thermoelectric phase...

Bi2Sr2Ca1Cu1.75Na0.25Oy ceramics have been prepared by the classical solid state reaction method followed by hot-pressing process under several applied pressures and temperatures: 22 and 33 MPa at 750 °C, and 22 MPa at 800 °C. X-ray diffraction data indicate that the major phase in all samples is the Bi2Sr2Ca1Cu1.75Na0.25Oy phase, accompanied by sm...

Bi2Sr2-xBaxCo2Oy polycrystalline samples (0.00 ≤ × ≤0.15) were prepared through the classical solid-state reaction method. It has been found that Ba-doped Bi2Sr2Co2Oy was obtained as major phase in all samples, based on XRD results. On the other hand, SEM studies have shown the presence of small amounts of secondary phases. The electrical resistivi...

This work studies the impact of metallic Ag addition on the microstructural, electrical, superconducting, and magnetic properties of Bi2Sr2Ca0.925Na0.075Cu2Oy. Samples with 0, 1, 3, 5 wt% were prepared from precursors produced by sol-gel method, followed by texturing through the laser floating zone (LFZ) technique. The normal state and residual res...

Ca 3 Co 4 O 9 + x wt% B 4 C, AlN, TiC, TiB 2 , or TiN (x = 0.0, 0.25, 0.50, and 0.75) samples were prepared by the conventional solid-state route. In all samples, only the Ca 3 Co 4 O 9 phase was identified by powder XRD. Nevertheless, microstructural studies have shown that most of the additives have reacted with air and Ca 3 Co 4 O 9 phase on the...

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...

This comprehensive study delves into the effect of partial Y³⁺ substitution for Ca²⁺ in Bi2Sr2CaCu2O8+y superconducting rods prepared by the laser floating zone method (LFZ). The critical transition temperatures (Tconset, Tc, Tcoffset), activation energy (U), irreversibility field (Hirr), upper critical magnetic field (Hc2), coherence length (ξ), a...

Strong thermal stress caused by high temperature and difference of thermal expansion coefficient (CTE) will negatively influence the lifespan of the thermoelectric module. In this work, a new high-temperature CaMnO3-based U-type unileg thermoelectric module, combining an unileg structure with pn-junction, is proposed and investigated. The novel des...

In this work, the effect of hot-pressing conditions on the performances of Sr-doped Ca3Co4O9 materials has been investigated. The samples were prepared from attrition milled precursors, which reduced the processing time. Samples were hot-pressed at temperatures (T) between 800 and 900 °C and pressures (P) from 51 to 71 MPa. The out-of-plane X-ray d...

In this work, Bi2Ca2-xNaxCo2Oy with x = 0.0, 0.05, 0.10, and 0.125 thermoelectric ceramic materials have been produced by the classical solid-state route, followed by texturing through the laser floating zone (LFZ) method. All specimens showed similar XRD patterns, with the main peaks corresponding to the (00l) plane reflections of the thermoelectr...

In the present study, thermoelectric Bi2Ca2-xKxCo2Oy ceramic materials (x=0.0, 0.05, 0.075, 0.10, and 0.125) in different forms (called bulk, as-grown and annealed fibers) have been manufactured via a classical solid-state method and textured using the laser floating zone (LFZ) technique. The identification and characteristics of undoped and doped...

This paper reports the microstructure, magnetoresistivity, electrical and superconducting properties of Bi-2212 fibers with Na+ ions incorporated into a superconducting matrix prepared by a polymer solution method and additionally textured through the laser floating zone process. XRD patterns showed that Bi-2212 phase is the major one with mostly (...

In the present study, thermoelectric Bi 2 Ca 2 − x K x Co 2 O y ceramic materials (x = 0.0, 0.05, 0.075, 0.10, and 0.125) in different forms (called bulk, as-grown and annealed fibers) have been manufactured via a classical solid-state method and textured using the laser floating zone (LFZ) technique. The identification and characteristics of undop...

Bi2Ca2−xNaxCo2Oy materials with x = 0 ≤ x ≤ 0.125, have been prepared either by sintering through the classical ceramic method, or textured using the laser floating zone technique. XRD results have shown that Bi2Ca2Co2Oy phase is the major one, independently of the Na content, in both kind of samples. SEM studies have shown a drastic microstructura...

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...

Bi2Sr2−xCsxCo2Oy materials with 0 ≤ x ≤ 0.15, have been fabricated via the classical ceramic technique. XRD results have indicated that undoped and Cs-substituted samples are composed of Bi2Sr2Co2Oy phase as the major one. Microstructural studies have demonstrated the formation of a liquid phase, which allows a drastic grain growth. This factor is...

Attrition milling is an easily scalable and environmentally friendly process used to produce Ca3Co4O9+δ nanoprecursors in a relatively short time. Sintered materials produced through the classical solid-state method, involving ball milling, show much larger grain sizes and slightly lower density than those obtained in samples produced from attritio...

Donor-doped CaMnO3 is an n-type semiconductor with perovskite structure, being considered as a potential n-type leg in thermoelectric modules. This oxide presents stability at high temperatures and allows tuning the relevant electrical and thermal transport properties through doping. In this work, Ca0.9Gd0.1MnO3 precursors have been prepared to pro...

Bi2Sr2-xRbxCo2O8+δ materials with 0 ≤ x ≤ 0.125 were fabricated via the classical solid-state route, and textured using the laser floating zone method. As-grown materials were composed of different secondary phases due to the incongruent melting of this compound. These secondary phases were drastically reduced through an annealing procedure, consis...

In this study, Bi2Sr2−xNaxCo2Oy (x = 0.0, 0.05, 0.075, 0.10, and 0.15) ceramic powders have been fabricated via the classical ceramic route, followed by a texturing process through the laser floating zone technique. XRD patterns show the thermoelectric phase as the major one. In addition, Na-substitution reduces the amount of secondary phases, when...

Ca3Co4O9 with B4C additions in different proportions (0, 0.10, 0.25, 0.5, and 0.75 wt.%) have been fabricated using the classical solid-state method. Powder XRD patterns have displayed that Ca3Co4O9 phase is the major one in all samples. Microstructural observations showed that B4C has been superficially oxidized, producing liquid B2O3 during sinte...

Within this study, Bi2Sr2Co1.8-xTixOy ceramic materials (x = 0, 0.05, 0.10, and 0.15) in different forms (bulk, as-grown and annealed fibers) have been produced through the solid state method and textured using the laser floating zone technique. XRD yields similar patterns for all sintered samples and annealed fibers, with major peaks corresponding...

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...

In this research, the effects of rubidium (Rb) substitution on the microstructural, physical, and superconducting properties of Bi2Sr2Ca1-xRbxCu2O8 + y with x = 0.0, 0.025, 0.05, 0.075, 0.10, and 0.125 superconductor have, in detail, been studied. For this purpose, samples were prepared through the classical solid state reaction route, followed by...

Thermoelectric performances of cobaltite ceramics were improved by increasing grain sizes and alignment through the Electrically Assisted Laser Floating Zone method. Bi2Sr2Co1.8Oy ceramics were directionally grown at 30 mm/h, applying external DC (0-500 mA) during the growth process. Microstructure and thermoelectric properties are significantly in...

B4C added Ca3Co4O9 in different proportions (0, 0.1, 0.25, 0.5, and 0.75 wt.%) have been fabricated using solid-state method. Powder XRD patterns have shown that only Ca3Co4O9 phase can be identified in all the samples. Microstructural observations have allowed determining that B4C compound has been superficially oxidized, producing liquid B2O3 pha...

Ca3Co4O9 + xwt.% TiC (x = 0, 0.25, 0.5, 0.75, and 1.0) polycrystalline thermoelectric ceramics have been prepared through the classical ceramic route. XRD characterization has demonstrated that all samples are mainly composed by the Ca3Co4O9 phase, while microstructural observation has shown that no reaction between both components has been produce...

Output power is a vital criterion in evaluating the heat-electricity conversion capability of thermoelectric power generators (TEGs). This study firstly proposes a novel (Bi,Sb)2Te3-based multilayer composite structured thermoelectric module (MCTEM) that can achieve high power output. Parallel heat transfer and electrical parallel connection are si...

In this work, the effect of cesium substitution on the structural and superconducting properties of Bi2Sr2Ca1-xCsxCu2O+y (where x = 0.0, 0.025, 0.050, 0.075, 0.10, 0.125, and 0.15) samples prepared by the solid-state reaction route and by directional growth using the laser floating zone (LFZ) technique has been studied. X-ray diffraction has shown...

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...

In this research, the effect of carbon nanotube (CNT) addition on the structural and superconducting properties of Bi2Sr2CaCu2Oy + x wt% CNT materials with x = 0, 0.5, 1, and 3 prepared by solid state method, followed by directional grown using the laser floating zone (LFZ) technique has been investigated. XRD measurements showed that all samples a...

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...

Sr‐doped Ca3Co4O9 thermoelectric thick films have been prepared by dip‐coating technique, followed by sintering and hot uniaxial pressing. XRD patterns are very similar in both types of samples, with only differences in the relative intensity of peaks, pointing out to a better grain orientation in hot‐pressed films. Moreover, SEM observation showed...

Bi2Sr2−xKxCo2Oy (x = 0.0, 0.025, 0.050, 0.075, 0.100, 0.125, and 0.15) ceramic materials have been fabricated using a classical ceramic process, followed by texturing through directional solidification. SEM analysis of samples, before and after annealing has shown that grains were aligned along the growth direction. While as-grown samples have seve...

Ca2.93Na0.07Co4Oy/x wt% K2CO3 (x = 0.00, 0.01, and 0.03) polycrystalline ceramics were prepared by conventional solid-state method. XRD results have shown that all samples predominantly include Ca3Co4O9 phase together with small amounts of secondary phases. SEM images show that all samples have randomly oriented plate-like grains in different sizes...

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...

In the present study, Bi 2 Sr 2-x K x Co 2 O y (x = 0.0, 0.050, 0.075, 0.100, and 0.15) ceramic precursors have been produced using the classical ceramic route, followed by texturing through the laser floating zone technique. XRD results show that the thermoelectric phase is the major one in all cases. Moreover, K-substitution decreases the seconda...

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...

Unileg-type thermoelectric generators have proven to be a good choice for high-temperature applications, because their composition from a single thermoelectric material avoids different thermal expansion coefficients, giving the structure good mechanical strength and increased lifespan during thermal cycling. These structures are usually composed o...

In this study, Ca0.9Yb0.1MnO3 + x wt.% Ag (with x = 0, 1, 3, 5, and 10) thermoelectric materials were prepared via the classical ceramic method. In spite of the very high sintering temperature (1300 °C), no significant Ag losses were observed following this process. Moreover, Ag addition enhanced cation mobility during sintering due to the formatio...

Ca3Co4O9 thermoelectric materials in form of thick films are very promising in practical applications due to their low costs and relatively high performance. In this work, two different suspensions have been used to produce different coatings on Al2O3 polycrystalline substrates with theoretical green thickness of 360 and 2000 µm. Moreover, the effe...

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...

In this study, polymerization method with polyethyleneimine, followed by hot-forging process was used to synthesize bulk textured Bi2Sr2Ca1−xNaxCu2Oy (x = 0.0, 0.05, 0.075 0.1, and 0.15) ceramics. Magnetoresistance performance of samples was studied by change of flux pinning mechanism. The effect of Na-substitution on the magnetoresistance, flux pi...

Bulk textured Ca2.93Sr0.07Co4O9 samples have been prepared by hot uniaxial pressing followed by thermal treatment at 800°C under air for between 0 h and 1532 h. The microstructural, thermoelectric, and mechanical properties as well as density of all the samples were evaluated as a function of the duration of thermal treatment. Scanning electron mic...

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...

This work presents a short and very efficient method to produce high performance textured Ca3Co4O9 thermoelectric materials through initial powders modification. Microstructure has shown good grain orientation, and low porosity while slightly lower grain sizes were obtained in samples prepared from attrition milled powders. All samples show the hig...

CuCrO2 and Cu0.97AE0.03CrO2 (AE = Mg, Ca, Sr, and Ba) polycrystalline materials have been prepared through the classical solid state route. CuCrO2 is the major phase in all cases, with larger grain sizes when the alkaline earth dopant is larger. Doping also promotes the formation of secondary phases, which appear in the grain boundaries in the Ca,...

CaMnO3-based materials are very attractive among n-type thermoelectric oxides for high-temperature applications when they are appropriately doped. The main drawback of these materials is the cost associated to the necessary rare earth cations. This work aims decreasing the amount of these materials through a partial substitution of Ca²⁺ by an equim...

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...

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...

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,...

In this work, Bi2Sr2−xKxCo2Ox thermoelectric materials with x = 0.0, 0.025, 0.050, 0.075, 0.10, 0.125, and 0.15 have been produced through the classical solid-state reaction. SEM characterization has shown an improvement of microstructure and a porosity decrease with K substitution, leading to very high densities, confirmed by apparent density meas...

The structural and magnetic properties evolution of Cr-doped Bi2Sr2CaCu2−xCrxOy ceramics (x = 0.0, 0.05, 0.1, and 0.25) have been investigated using XRD, SEM, DC resistivity and M–H measurements. X-ray diffraction studies have shown that all samples are mainly composed of Bi-2212 phase, indicating that Cr can be incorporated in its crystal structur...

Bi2Sr2-xNaxCo2Ox (x=0.0, 0.025, 0.050, 0.075, 0.100, and 0.125) samples were prepared through the solid-state route and textured using the laser floating zone technique. Microstructural analysis of as-grown samples showed well oriented grains and a relatively high amount of secondary phases due to their incongruent melting. Annealing procedure has...

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...

This work focuses on the photothermoelectric (PTE) technique allowing the thermal characterization of solid-state thermoelectric (TE) materials. Previously, this technique was restricted to TE materials having low electrical conductivities. Here, the PTE technique is extended and generalized to all solid-state TE materials with low or high electric...

Ca0.9Yb0.1MnO3 thermoelectric materials have been prepared, through a classical solid state sintering method, from attrition, and ball milled precursors. After calcination step, microstructural observations have shown that attrition milled precursors possess much smaller particle sizes than the obtained by ball milling. Smaller precursors sizes lea...

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...

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...

High density bulk CdO polycrystalline thermoelectric ceramics have been prepared through a hot-pressing process. Density measurements have revealed that it reaches 99.5% of the theoretical one, in agreement with the observed microstructure. Microhardness has shown to have indentation size effect, decreasing when the load is raised. Electrical resis...

The effect of Ag addition on the structural and superconducting properties of Bi2Sr2Ca0.925Na0.075Cu2Oy + x wt% Ag materials with x = 0, 1, 3, and 5 prepared by sol–gel method, followed by directional growth using the laser floating zone (LFZ) technique has been investigated. Powder XRD measurements demonstrate that all samples are composed by near...

[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 tha...

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...

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...

Higher efficiency, power density, reliability and longer lifetime of power electronic devices would stem from progresses in material science. In this work, we propose to use a high performance thermoplastic polymer PAEK as packaging box to extend the operating temperature above 200°C. More, the laser transmission welding process has been applied to...