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Papers by Mieczyslaw Rekas
Materialy Ceramiczne Ceramic Materials, 2011
Solid State Ionics, 1986
Abstract Electrical conductivity of undoped and Sb-doped BaTiO3 are measured under PO2 between 2×... more Abstract Electrical conductivity of undoped and Sb-doped BaTiO3 are measured under PO2 between 2×10-14 and 105 Pa in the temperature range 1123–1273 K. Both powers of the oxygen pressure dependence and activation energies of electrical conductivity are determined. It has been concluded that the mechanism of Sb incorporation into BaTiO3 depends on composition. At lower concentrations (below 0.15 mo1% Sb2O5) Sb incorporates into both Ba and Ti sublattices froming donor centers. Above this concentration Sb incorporates preferentially into Ti sites forming acceptor centers.
Functional Materials Letters, 2011
La 1-x Mg x OCl 1-x (x = 0.025, 0.05 and 0.1) and La 0.9 Ca 0.1 OCl 0.9 samples were prepared by ... more La 1-x Mg x OCl 1-x (x = 0.025, 0.05 and 0.1) and La 0.9 Ca 0.1 OCl 0.9 samples were prepared by a solid state reaction method. The best preparation conditions were determined by means of the differential thermal analysis and thermogravimetry (DTA&TG). The samples were studied by X-ray diffraction (XRD) analysis. Electrical conductivity of La 0.9 Mg 0.1 OCl 0.1 was measured using electrical impedance spectroscopy (EIS). The prototype chlorine gas sensor was constructed from La 0.9 Mg 0.1 OCl 0.1 solid electrolyte. The source voltage (SV) of the constructed device was measured as a function of temperature (500–800°C), Cl 2 gradient partial pressure and time. Similar measurements of SV was carried out in atmosphere of synthetic air in argon.
Solid State Ionics, 1986
Abstract Electrical conductivity σ and thermopower α were studied at temperature 1150–1350 K and ... more Abstract Electrical conductivity σ and thermopower α were studied at temperature 1150–1350 K and in the P O 2 range between 2×10 -11 -2×10 4 Pa. Both σ and α data are well consistent, n - and p -type conductivity ranges were found at low and high P O 2 values, respectively. The power of P O 2 dependence for Cu-doped BaTiO 3 vary the oxide composition. This effect is discussed in term of the defect structure of BaTiO 3 and its solutions with CuO.
Functional Materials Letters, 2011
Silver and yttrium dopants influence some physico-chemical properties of BaCeO 3 protonic conduct... more Silver and yttrium dopants influence some physico-chemical properties of BaCeO 3 protonic conduction. Ag -acceptor dopant substituting Ba atom in BaCeO 3 compounds was studied for the first time. Ba 1-x Ag x Ce 1-y Y y O 3-δ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1) materials were synthesized by solid state reaction and by modified Pechini citric acid method. X-ray diffraction (XRD) and electrical properties measurements including open cell voltage (OCV) of electrochemical cells were used as experimental techniques. Basing on XRD results it was found that all synthesized materials crystallized in orthorhombic Pnma phase with some admixtures of other phases. Metallic Ag , CeO 2 or Y 2 O 3 with different concentrations were detected, depending on the composition, synthesis method and preparation details. DC electrical measurements showed that doping by Ag and Y decreased the total and ionic conductivities of the materials. The modification of charge transport properties was also observed, namely int...
Bulletin of The Polish Academy of Sciences-chemistry, 2001
Two different complexing agents, namely citric acid and gelatin, were used for gel-combustion syn... more Two different complexing agents, namely citric acid and gelatin, were used for gel-combustion synthesis of yttria stabilized zirconia. The influence of synthesis conditions on properties of powders and sintered bodies was studied by X-ray Diffraction Analysis (XRD), Scanning Electron Microscope (SEM) and helium pycnometer measurements.
Bulletin of The Polish Academy of Sciences-chemistry, 2001
Materialy Ceramiczne Ceramic Materials, 2014
Materialy Ceramiczne Ceramic Materials, 2011
Materialy Ceramiczne Ceramic Materials, 2011
Planar electrolyte-supported solid oxide fuel cells were studied. Dense membranes of the dimensio... more Planar electrolyte-supported solid oxide fuel cells were studied. Dense membranes of the dimensions: 100 x 100 mm and a thickness of 130 �m, made from yttria-stabilized zirconia (both tetragonal and cubic) were used as solid electrolytes. Ni-zirconia c ermet and La0.8Sr0.2MnO3 layers were deposited on the surfaces of the electrolyte as the anode and the cathode, respectively. Electrochemical impedance spectroscopy was used in order to characterize the electrical properties of the solid electrolyte membranes and the electrolyte-anode and electrolyte-cathode systems. It was found that an equivalent circuit is composed of two series of resistor- constant phase element connected in parallel. No additional elements in the equivalent circuit originated from either the anode or the cathode layers have been observed with respect to the single electrolyte sample.
Ogniwa paliwowe s aktualnie najbardziej efektywnymi urz dzeniami wytwarzaj cymi energi elektryczn... more Ogniwa paliwowe s aktualnie najbardziej efektywnymi urz dzeniami wytwarzaj cymi energi elektryczn z paliw kopalnianych, g ownie gazu ziemnego. W perspektywie stanowi mog powa n konkurencj dla powszechnie stosowanych do nap du pojazdow silnikow spalinowych. Jednak e, aby by y szerzej stosowane powinny one spe nia nast puj ce wymogi: – wysoka wydajno konwersji energii (powy ej 40%), – d ugotrwa a eksploatacja (powy ej 40 000 godzin 4,5 lat), – niskie koszty wytwarzania i eksploatacji. Aby osi gn te cele prowadzone s intensywne prace obejmuj ce mody kacje dotychczasowo znanych typow ogniw. Najwi ksze nadzieje zwi zane s z najbardziej efektywnym typem ogniw tj. sta o-tlenkowym ogniwem paliwowym (SOFC – Solid Oxide Fuel Cell) o efektywno ci od 50-60%. SOFC ciesz si najwi kszym zainteresowaniem z powodu ich wysokiej wydajno ci oraz niskich ogranicze odno nie rodzaju i czysto ci paliwa. Mo na w nich stosowa gaz ziemny, wodor lub biogaz jako paliwo. Ponadto ogniwa te daj mo liwo atwego odzyskiwania ciep a. Poziom gaFormowanie submikronowych i nanometrycznych proszkow cyrkoniowych dla zastosowa w ogniwach paliwowych
Materialy Ceramiczne Ceramic Materials, 2010
Flame spray synthesis (FSS) was used to grow TiO2-based nanopowders from which TiO2:Cr nanosensor... more Flame spray synthesis (FSS) was used to grow TiO2-based nanopowders from which TiO2:Cr nanosensors were obtained. Structural properties of crystalline TiO2:Cr nanopowders at different Cr loadings (0.1-5.0 at.%) have been investigated. Material studies have been performed using standard methods: X-ray diffraction (XRD) transmission electron microscopy (TEM) and Brunauer-Emmett-Teller adsorption isotherms analysis (BET). High specic surface area (37-126 m 2/g) and small crystallite size (9-27 nm) have been reached. Incorporation of Cr into TiO2 lattice affects the specic surface area of nanopowders, the crystallite size and the rutile to anatase ratio. Gas sensing characteristics of TiO2:Cr nanosensors upon interaction with H2 have been recorded in the self-assembled experimental system. The detection of hydrogen was carried out over the concentration range of 50-3000 ppm at the temperatures extending from 200 to 400oC. It is demonstrated that nanomaterials based on TiO2:Cr are attractive for ultimate sensors applications due to a decrease in the operating temperature down to 210-250oC, accompanied by an increase in the sensor response. Taking into account the possible operating costs, the best candidates for the commercial use are TiO2:1 at.% Cr and TiO2:5 at.% Cr nanosensors.
Materials, 2022
Composite tetragonal zirconia (3Y-TZP) sinters with Al2O3 contents of 0, 1, 5, 10 and 15 mol% wer... more Composite tetragonal zirconia (3Y-TZP) sinters with Al2O3 contents of 0, 1, 5, 10 and 15 mol% were obtained from a 3-YSZ powder prepared using the gelatin method, and the influence of alumina addition on the mechanical and electrical properties of the obtained sinters was investigated. Al2O3 was added via two different methods, namely during the preparation of the 3-YSZ powder and via impregnation using an alcohol solution of aluminum nitrate. The obtained green bodies were sintered for 2 h in air at 1773 K. The structure and morphology of the two series of sinters were investigated using XRD and SEM-EDS, their electrical properties were determined using impedance spectroscopy, and their hardness and critical stress intensity factor were measured using the Vickers indentation test. We established that both the amount of alumina and the method used to introduce it into the 3Y-TZP matrix significantly affect the physicochemical properties of the obtained polycrystalline material. The ...
Journal of the American Ceramic Society, 2014
Journal of the European Ceramic Society, 1989
Abstract Both electrical conductivity (σ) and thermopower (α) data are reported within the p-type... more Abstract Both electrical conductivity (σ) and thermopower (α) data are reported within the p-type regime for undoped BaTiO 3 in the temperature range 1268–1418 K. The experimental data are considered against several models of the BaTiO 3 defect structure. It has been documented that both electron holes and electrons participate in the conduction process. It has been argued that electron holes may be generated as a result of different processes such as ionization of acceptor-type impurities and intrinsic defects. In considerations of the defect models it has been assumed that within the p-type regime the concentration of oxygen vacancies is negligibly low and predominant defects are both cation vacancies and acceptor-type extrinsic defects. Thus the determined intrinsic equilibrium constant is the following function of p O 2 and temperature: K=[V″ Ba ][V⁗ Ti ][h] 6 p O 2 −3 2 =3·1 × 10 −29 exp(− 3·65[eV] kT )
Materialy Ceramiczne Ceramic Materials, 2011
Solid State Ionics, 1986
Abstract Electrical conductivity of undoped and Sb-doped BaTiO3 are measured under PO2 between 2×... more Abstract Electrical conductivity of undoped and Sb-doped BaTiO3 are measured under PO2 between 2×10-14 and 105 Pa in the temperature range 1123–1273 K. Both powers of the oxygen pressure dependence and activation energies of electrical conductivity are determined. It has been concluded that the mechanism of Sb incorporation into BaTiO3 depends on composition. At lower concentrations (below 0.15 mo1% Sb2O5) Sb incorporates into both Ba and Ti sublattices froming donor centers. Above this concentration Sb incorporates preferentially into Ti sites forming acceptor centers.
Functional Materials Letters, 2011
La 1-x Mg x OCl 1-x (x = 0.025, 0.05 and 0.1) and La 0.9 Ca 0.1 OCl 0.9 samples were prepared by ... more La 1-x Mg x OCl 1-x (x = 0.025, 0.05 and 0.1) and La 0.9 Ca 0.1 OCl 0.9 samples were prepared by a solid state reaction method. The best preparation conditions were determined by means of the differential thermal analysis and thermogravimetry (DTA&TG). The samples were studied by X-ray diffraction (XRD) analysis. Electrical conductivity of La 0.9 Mg 0.1 OCl 0.1 was measured using electrical impedance spectroscopy (EIS). The prototype chlorine gas sensor was constructed from La 0.9 Mg 0.1 OCl 0.1 solid electrolyte. The source voltage (SV) of the constructed device was measured as a function of temperature (500–800°C), Cl 2 gradient partial pressure and time. Similar measurements of SV was carried out in atmosphere of synthetic air in argon.
Solid State Ionics, 1986
Abstract Electrical conductivity σ and thermopower α were studied at temperature 1150–1350 K and ... more Abstract Electrical conductivity σ and thermopower α were studied at temperature 1150–1350 K and in the P O 2 range between 2×10 -11 -2×10 4 Pa. Both σ and α data are well consistent, n - and p -type conductivity ranges were found at low and high P O 2 values, respectively. The power of P O 2 dependence for Cu-doped BaTiO 3 vary the oxide composition. This effect is discussed in term of the defect structure of BaTiO 3 and its solutions with CuO.
Functional Materials Letters, 2011
Silver and yttrium dopants influence some physico-chemical properties of BaCeO 3 protonic conduct... more Silver and yttrium dopants influence some physico-chemical properties of BaCeO 3 protonic conduction. Ag -acceptor dopant substituting Ba atom in BaCeO 3 compounds was studied for the first time. Ba 1-x Ag x Ce 1-y Y y O 3-δ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1) materials were synthesized by solid state reaction and by modified Pechini citric acid method. X-ray diffraction (XRD) and electrical properties measurements including open cell voltage (OCV) of electrochemical cells were used as experimental techniques. Basing on XRD results it was found that all synthesized materials crystallized in orthorhombic Pnma phase with some admixtures of other phases. Metallic Ag , CeO 2 or Y 2 O 3 with different concentrations were detected, depending on the composition, synthesis method and preparation details. DC electrical measurements showed that doping by Ag and Y decreased the total and ionic conductivities of the materials. The modification of charge transport properties was also observed, namely int...
Bulletin of The Polish Academy of Sciences-chemistry, 2001
Two different complexing agents, namely citric acid and gelatin, were used for gel-combustion syn... more Two different complexing agents, namely citric acid and gelatin, were used for gel-combustion synthesis of yttria stabilized zirconia. The influence of synthesis conditions on properties of powders and sintered bodies was studied by X-ray Diffraction Analysis (XRD), Scanning Electron Microscope (SEM) and helium pycnometer measurements.
Bulletin of The Polish Academy of Sciences-chemistry, 2001
Materialy Ceramiczne Ceramic Materials, 2014
Materialy Ceramiczne Ceramic Materials, 2011
Materialy Ceramiczne Ceramic Materials, 2011
Planar electrolyte-supported solid oxide fuel cells were studied. Dense membranes of the dimensio... more Planar electrolyte-supported solid oxide fuel cells were studied. Dense membranes of the dimensions: 100 x 100 mm and a thickness of 130 �m, made from yttria-stabilized zirconia (both tetragonal and cubic) were used as solid electrolytes. Ni-zirconia c ermet and La0.8Sr0.2MnO3 layers were deposited on the surfaces of the electrolyte as the anode and the cathode, respectively. Electrochemical impedance spectroscopy was used in order to characterize the electrical properties of the solid electrolyte membranes and the electrolyte-anode and electrolyte-cathode systems. It was found that an equivalent circuit is composed of two series of resistor- constant phase element connected in parallel. No additional elements in the equivalent circuit originated from either the anode or the cathode layers have been observed with respect to the single electrolyte sample.
Ogniwa paliwowe s aktualnie najbardziej efektywnymi urz dzeniami wytwarzaj cymi energi elektryczn... more Ogniwa paliwowe s aktualnie najbardziej efektywnymi urz dzeniami wytwarzaj cymi energi elektryczn z paliw kopalnianych, g ownie gazu ziemnego. W perspektywie stanowi mog powa n konkurencj dla powszechnie stosowanych do nap du pojazdow silnikow spalinowych. Jednak e, aby by y szerzej stosowane powinny one spe nia nast puj ce wymogi: – wysoka wydajno konwersji energii (powy ej 40%), – d ugotrwa a eksploatacja (powy ej 40 000 godzin 4,5 lat), – niskie koszty wytwarzania i eksploatacji. Aby osi gn te cele prowadzone s intensywne prace obejmuj ce mody kacje dotychczasowo znanych typow ogniw. Najwi ksze nadzieje zwi zane s z najbardziej efektywnym typem ogniw tj. sta o-tlenkowym ogniwem paliwowym (SOFC – Solid Oxide Fuel Cell) o efektywno ci od 50-60%. SOFC ciesz si najwi kszym zainteresowaniem z powodu ich wysokiej wydajno ci oraz niskich ogranicze odno nie rodzaju i czysto ci paliwa. Mo na w nich stosowa gaz ziemny, wodor lub biogaz jako paliwo. Ponadto ogniwa te daj mo liwo atwego odzyskiwania ciep a. Poziom gaFormowanie submikronowych i nanometrycznych proszkow cyrkoniowych dla zastosowa w ogniwach paliwowych
Materialy Ceramiczne Ceramic Materials, 2010
Flame spray synthesis (FSS) was used to grow TiO2-based nanopowders from which TiO2:Cr nanosensor... more Flame spray synthesis (FSS) was used to grow TiO2-based nanopowders from which TiO2:Cr nanosensors were obtained. Structural properties of crystalline TiO2:Cr nanopowders at different Cr loadings (0.1-5.0 at.%) have been investigated. Material studies have been performed using standard methods: X-ray diffraction (XRD) transmission electron microscopy (TEM) and Brunauer-Emmett-Teller adsorption isotherms analysis (BET). High specic surface area (37-126 m 2/g) and small crystallite size (9-27 nm) have been reached. Incorporation of Cr into TiO2 lattice affects the specic surface area of nanopowders, the crystallite size and the rutile to anatase ratio. Gas sensing characteristics of TiO2:Cr nanosensors upon interaction with H2 have been recorded in the self-assembled experimental system. The detection of hydrogen was carried out over the concentration range of 50-3000 ppm at the temperatures extending from 200 to 400oC. It is demonstrated that nanomaterials based on TiO2:Cr are attractive for ultimate sensors applications due to a decrease in the operating temperature down to 210-250oC, accompanied by an increase in the sensor response. Taking into account the possible operating costs, the best candidates for the commercial use are TiO2:1 at.% Cr and TiO2:5 at.% Cr nanosensors.
Materials, 2022
Composite tetragonal zirconia (3Y-TZP) sinters with Al2O3 contents of 0, 1, 5, 10 and 15 mol% wer... more Composite tetragonal zirconia (3Y-TZP) sinters with Al2O3 contents of 0, 1, 5, 10 and 15 mol% were obtained from a 3-YSZ powder prepared using the gelatin method, and the influence of alumina addition on the mechanical and electrical properties of the obtained sinters was investigated. Al2O3 was added via two different methods, namely during the preparation of the 3-YSZ powder and via impregnation using an alcohol solution of aluminum nitrate. The obtained green bodies were sintered for 2 h in air at 1773 K. The structure and morphology of the two series of sinters were investigated using XRD and SEM-EDS, their electrical properties were determined using impedance spectroscopy, and their hardness and critical stress intensity factor were measured using the Vickers indentation test. We established that both the amount of alumina and the method used to introduce it into the 3Y-TZP matrix significantly affect the physicochemical properties of the obtained polycrystalline material. The ...
Journal of the American Ceramic Society, 2014
Journal of the European Ceramic Society, 1989
Abstract Both electrical conductivity (σ) and thermopower (α) data are reported within the p-type... more Abstract Both electrical conductivity (σ) and thermopower (α) data are reported within the p-type regime for undoped BaTiO 3 in the temperature range 1268–1418 K. The experimental data are considered against several models of the BaTiO 3 defect structure. It has been documented that both electron holes and electrons participate in the conduction process. It has been argued that electron holes may be generated as a result of different processes such as ionization of acceptor-type impurities and intrinsic defects. In considerations of the defect models it has been assumed that within the p-type regime the concentration of oxygen vacancies is negligibly low and predominant defects are both cation vacancies and acceptor-type extrinsic defects. Thus the determined intrinsic equilibrium constant is the following function of p O 2 and temperature: K=[V″ Ba ][V⁗ Ti ][h] 6 p O 2 −3 2 =3·1 × 10 −29 exp(− 3·65[eV] kT )