Juan Carlos Ruiz Morales | Universidad de La Laguna (original) (raw)
Papers by Juan Carlos Ruiz Morales
RSC Advances, 2013
ABSTRACT Here we explore into the lately emerging ground-breaking photonic approach to enhance ph... more ABSTRACT Here we explore into the lately emerging ground-breaking photonic approach to enhance photocatalytic activity of main semiconductors electrodes used in water-splitting such as titanium dioxide (TiO2): the blue shift of the incident radiation by means of high-efficient upconversion in rare-earth (RE) doped luminescent materials to assist long wavelength harvesting of unused portions of infrared light. We present an up to 20% improvement of the photocatalytic action in the decomposition of methylene blue in water under Xe-lamp irradiation of commercial benchmark TiO2 efficient photocatalyst, and also an outstanding enhancement by factor of about 2.5 of photolysis in this pollutant degradation rate. Our results prove that the ultraviolet (UV) radiation that reaches the TiO2 particles has been increased by the addition of RE-doped material’s powder into a slurry-type photo-reactor, boosting both photocatalysis and photolysis degradation rate. Thus we show the feasibility of handling and transforming the incoming infrared radiation, bridging the UV gap of photocatalytic semiconductors. Let us turn the infrared into the blue; there is plenty of energy at the bottom.
Journal of Power Sources, 2013
ABSTRACT The use of hydrogen to feed Fuel Cells emerges as an attractive renewable solution to me... more ABSTRACT The use of hydrogen to feed Fuel Cells emerges as an attractive renewable solution to meet the terawatt carbon-neutral energy demand challenge. Rare-earth doped nano-glass-ceramics, presenting outstanding high intense UV-blue up-conversion processes, appear as an interesting approach to assist long wavelength light harvesting of solar irradiation, extending the photo-catalytic response to the red and near-infrared region to overcome the drawback of large band-gap materials used in the splitting of water into oxygen and hydrogen in a photo-electrochemical cell.
Journal of Luminescence, 2013
ABSTRACT High efficient UV-VIS up-conversion luminescence of Er3+ and Tm3+ ions sensitized by Yb3... more ABSTRACT High efficient UV-VIS up-conversion luminescence of Er3+ and Tm3+ ions sensitized by Yb3+ ions in ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fluoride glasses have been obtained under near-infrared excitation at 980 nm. Red, green and blue simultaneous emissions were observed yielding to a white-balanced overall colour. Moreover significant high intense UV up-conversion emissions observed can contribute to enhance spectral response of semiconductor electrode, such as TiO2 and Fe2O3, for sustainable production of hydrogen via water photolysis by harvesting of long wavelength solar irradiation, emerging as an interesting solely luminescent approach for improving water-splitting. Total infrared to UV-VIS up-conversion efficiency has been calculated to be at around 46%. Preliminary laboratory tests prove the improvement in the photocatalytic action of a commercial benchmark photocatalyst (TiO2 Degussa P25) in the decomposition of methylene blue in water under sun-like irradiation, by a factor of 16% driven by up-conversion effects due to the inclusion of RE-doped ZBLAN powders into a slurry-type photo-reactor.
Catalysis Today, 2013
ABSTRACT Heterogeneous photocatalysis based on TiO2 materials is an interesting method for the tr... more ABSTRACT Heterogeneous photocatalysis based on TiO2 materials is an interesting method for the treatment of polluted water because it allows degradation of a wide variety of organic contaminant compounds. The performance of TiO2 based photocatalysts was studied by aqueous solutions of methylene blue (MB) as a model contaminant compound by using 50 mg L−1 as initial water contaminant concentration in order to compare the photocatalytic behaviour of TiO2 Degussa P25 and some synthesized photocatalysts by hydrothermal treatment (nanostructured TiO2 and metal-doped nanostructured TiO2 photocatalysts: nanostructured Co–TiO2, nanostructured Fe–TiO2 and nanostructured Mn–TiO2) under UV and visible light irradiation. Photocatalytic materials characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption, mercury porosimetry, XPS and diffuse reflectance UV–vis spectra. An improvement of the photocatalytic activity has been observed when nanostructured and doped photocatalysts were used under visible light irradiation, concluding that the hydrothermal treatment produces a nanostructuration of commercial titania by the formation of nanoparticles, which results in a large decrease of average crystallite size of undoped and doped titania, and in an important increase of BET specific area and total pore area.
A pesar de que su presencia de un modo relevante en los medios de comunicación es relativamente r... more A pesar de que su presencia de un modo relevante en los medios de comunicación es relativamente reciente, las pilas de combustible se conocen desde hace más de 150 años. Los estudios pioneros de Schönbein y Grove dieron origen a la tecnología de pilas de combustible que es la que conocemos hoy en día. Posteriormente numerosos investigadores han ido aportando nuevas ideas en los campos de materiales, electroquímica, combustibles, ingeniería, etc..., para acabar definiendo los diferentes tipos de pilas que conocemos actualmente. Esta interacción entre numerosos campos de investigación, a menudo interdisciplinares, ha dado lugar en los últimos 15 años a un aumento considerable, tanto desde el punto de vista de los resultados producidos como de las inversiones a nivel privado y público. Parte de ese esfuerzo investigador e inversor viene motivado por el cambio climático y/o el agotamiento de las reservas de combustibles fósiles en los que se basa el modelo energético actual, lo que ha o...
Boletin de la Sociedad Espanola de Ceramica y Vidrio
The performance and the potential application of the cubic members of the La(4)Sr(n-4)Ti(n)O(3n+2... more The performance and the potential application of the cubic members of the La(4)Sr(n-4)Ti(n)O(3n+2) series of compounds, i.e. n≥12, prepared by solid state reaction are discussed. Although these phases can be indexed as cubic perovskites by XRD, there exists some oxygen beyond the ABO3 stoichiometry accommodated in linear defects reminiscent to the oxygen rich layers in La2Ti2O7. Fuel cell tests reveal that these materials exhibit moderate responses under hydrogen, but also some promising results implying activation favouring methane oxidation.
En este trabajo revisamos brevemente las pilas de combustible poliméricas (PEM) basadas en membra... more En este trabajo revisamos brevemente las pilas de combustible poliméricas (PEM) basadas en membranas de intercambio protónico y que constituyen la tecnología idónea de pilas de combustible de baja temperatura, y por tanto las más adecuadas para aplicación en transporte. Revisaremos los materiales que las componen pero también los desarrollos necesarios para su implantación definitiva en un mercado inclemente con las tecnologías caras, por limpias que sean. Palabras claves: pila de combustible, membrana polimérica, PEMFC, catalizador, electrolíto SUMMARY In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, which are the ideal technology for fuel cells at low temperature, and therefore more suitable for use in transportation. We will review the materials that compose them, but also the necessary developments for its final implementation in a market that it is not friendly with expensive technologies, even they are clean.
Afinidad -Barcelona-
In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, whic... more In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, which are the ideal technology for fuel cells at low temperature, and therefore more suitable for use in transportation. We will review the materials that compose them, but also the necessary developments for its final implementation in a market that it is not friendly with expensive technologies, even they are clean.
Solid State Ionics, 2005
A modified freeze-dried method has been used to obtain polycrystalline powders of the ionic condu... more A modified freeze-dried method has been used to obtain polycrystalline powders of the ionic conductor La2Mo2O9. Such ceramic powders were characterized by TG/DTA, XRD, SEM and TEM, and their sinterability was analysed by dilatometry and isothermal sintering ...
Fuel Cells, 2008
The layered perovskite GdBaCo 2 O 5 + d (GBCO), recently proposed for intermediate temperature so... more The layered perovskite GdBaCo 2 O 5 + d (GBCO), recently proposed for intermediate temperature solid oxide fuel cell applications, was investigated and compared with Ba 0.5 Sr 0.5 -Co 0.8 Fe 0.2 O 3d (BSCF) cathode material using La 0.9 A 0.1 -Ga 0.8 Mg 0.2 O 2.85 (A=Sr,Ba) as electrolytes. Area-specific resistance was measured by impendance spectroscopy in symmetrical cells. The cobaltites were prepared by a modified citrate sol-gel route and tested as cathode materials for doped lanthanum gallate-based cells using dry H 2 as fuel and air as oxidant, rendering power density values of 180 and 240 mW cm -2 at 1,073 K (1 mm thick pellets) for GBCO and BSCF fuel cells, respectively.
ChemInform, 2008
Preparation of Thin Layer Materials with Macroporous Microstructure for SOFC Applications. -Thin ... more Preparation of Thin Layer Materials with Macroporous Microstructure for SOFC Applications. -Thin layer oxide materials generally used in solid oxide fuel cells and catalytic applications with fluorite and perovskite-type structures such as doped zirconia, ceria, ferrites, manganites, and NiO-YSZ composites are prepared with controlled macroporous microstructure using polymethyl methacrylate microspheres as pore formers. The materials exhibit homogeneous pore distributions with relatively high specific surface areas between 11 and 38 m 2 /g after calcination between 450 and 650°C. The samples are characterized by XRD, SEM, TEM, nitrogen adsorption, and mercury porosimetry. These film materials possibly exhibit better performance for solid oxide fuel cell application in the intermediate temperature range than usual electrodes made of polycrystalline materials. -(MARRERO-LOPEZ, D.; RUIZ-MORALES, J. C.; PENA-MARTINEZ, J.; CANALES-VAZQUEZ, J.; NUNEZ*, P.; J. Solid State Chem. 181 (2008) 4, 685-692; Dep. Quim. Inorg., Univ.
Here we report two novel procedures that may lead to enhanced efficiencies of a SOFC via a precis... more Here we report two novel procedures that may lead to enhanced efficiencies of a SOFC via a precise control of the electrode microstructure and through the fabrication of a new type of electrolyte-supported SOFC. The first route is a simple and cost-effective method that ...
ABSTRACT Conference code: 69824, Export Date: 24 December 2012, Source: Scopus, CODEN: MRSPD, Lan... more ABSTRACT Conference code: 69824, Export Date: 24 December 2012, Source: Scopus, CODEN: MRSPD, Language of Original Document: English, Correspondence Address: Ruiz-Morales, J.C.; Department of Inorganic Chemistry, University of La Laguna, Avda. Astrofisico Fco. Sanchez, s/n, La Laguna, E-38200, Spain, References: Minh, N.Q., Takahashi, T., (1995) Science and Technology of Ceramic Fuel Cells, , Elsevier, Amsterdam;
ABSTRACT The characteristics of a solid oxide fuel cell cathode are investigated using a combinat... more ABSTRACT The characteristics of a solid oxide fuel cell cathode are investigated using a combination of scanning electron microscopy, electrochemical impedance spectroscopy and simulations using the state-space model (SSM). We successfully explain the shape of the impedance spectrum at several temperatures, determine kinetic parameters, measure the triple phase boundary length and deduce its width. Finally a quantitative analysis of the constant phase element using surface roughness and energy activation distribution is presented. © 2009 Elsevier B.V. All rights reserved.
Journal of the European Ceramic Society, 2013
Gd-doped ceria nanopowders have been synthesized via a modified sol-gel technique using different... more Gd-doped ceria nanopowders have been synthesized via a modified sol-gel technique using different pyrolysis temperatures to produce a range of particle sizes. Such nanocrystalline oxides have been sintered at 1400 • C for 24 h to produce fully dense disks. The microstructural characterization reveals that the pyrolysis temperature notably affects the grain size distribution in the sintered ceramics, e.g. powders treated at 700 • C render the narrowest grain size distribution. The electrochemical characterisation performed by electrochemical impedance spectroscopy shows that the distribution of grain sizes in the dense electrolytes rules the electrical conductivity of CGOs rather than the average grain size. Narrower grain size distributions render electrolytes exhibiting higher overall conductivity, independent of the average grain size.
A synthesis method based on freeze-dried precursors was used to obtain nanocrystalline powders of... more A synthesis method based on freeze-dried precursors was used to obtain nanocrystalline powders of pure and Ca-doped LaNbO 4 at 800 • C. Dense ceramics were prepared at temperature as low as 1100 • C. The LaNbO 4 ceramics were examined by scanning electron microscopy (SEM) to study the microstructure evolution with the sintering temperature. The densification and grain growth rate are lower in Ca-doped samples. The bulk and grain boundary contributions to the overall conductivity were studied by impedance spectroscopy under different gases. Samples sintered at low temperature and with smaller grain size exhibit higher grain boundary resistance and consequently lower total conductivity.
RSC Advances, 2013
ABSTRACT Here we explore into the lately emerging ground-breaking photonic approach to enhance ph... more ABSTRACT Here we explore into the lately emerging ground-breaking photonic approach to enhance photocatalytic activity of main semiconductors electrodes used in water-splitting such as titanium dioxide (TiO2): the blue shift of the incident radiation by means of high-efficient upconversion in rare-earth (RE) doped luminescent materials to assist long wavelength harvesting of unused portions of infrared light. We present an up to 20% improvement of the photocatalytic action in the decomposition of methylene blue in water under Xe-lamp irradiation of commercial benchmark TiO2 efficient photocatalyst, and also an outstanding enhancement by factor of about 2.5 of photolysis in this pollutant degradation rate. Our results prove that the ultraviolet (UV) radiation that reaches the TiO2 particles has been increased by the addition of RE-doped material’s powder into a slurry-type photo-reactor, boosting both photocatalysis and photolysis degradation rate. Thus we show the feasibility of handling and transforming the incoming infrared radiation, bridging the UV gap of photocatalytic semiconductors. Let us turn the infrared into the blue; there is plenty of energy at the bottom.
Journal of Power Sources, 2013
ABSTRACT The use of hydrogen to feed Fuel Cells emerges as an attractive renewable solution to me... more ABSTRACT The use of hydrogen to feed Fuel Cells emerges as an attractive renewable solution to meet the terawatt carbon-neutral energy demand challenge. Rare-earth doped nano-glass-ceramics, presenting outstanding high intense UV-blue up-conversion processes, appear as an interesting approach to assist long wavelength light harvesting of solar irradiation, extending the photo-catalytic response to the red and near-infrared region to overcome the drawback of large band-gap materials used in the splitting of water into oxygen and hydrogen in a photo-electrochemical cell.
Journal of Luminescence, 2013
ABSTRACT High efficient UV-VIS up-conversion luminescence of Er3+ and Tm3+ ions sensitized by Yb3... more ABSTRACT High efficient UV-VIS up-conversion luminescence of Er3+ and Tm3+ ions sensitized by Yb3+ ions in ZrF4–BaF2–LaF3–AlF3–NaF (ZBLAN) fluoride glasses have been obtained under near-infrared excitation at 980 nm. Red, green and blue simultaneous emissions were observed yielding to a white-balanced overall colour. Moreover significant high intense UV up-conversion emissions observed can contribute to enhance spectral response of semiconductor electrode, such as TiO2 and Fe2O3, for sustainable production of hydrogen via water photolysis by harvesting of long wavelength solar irradiation, emerging as an interesting solely luminescent approach for improving water-splitting. Total infrared to UV-VIS up-conversion efficiency has been calculated to be at around 46%. Preliminary laboratory tests prove the improvement in the photocatalytic action of a commercial benchmark photocatalyst (TiO2 Degussa P25) in the decomposition of methylene blue in water under sun-like irradiation, by a factor of 16% driven by up-conversion effects due to the inclusion of RE-doped ZBLAN powders into a slurry-type photo-reactor.
Catalysis Today, 2013
ABSTRACT Heterogeneous photocatalysis based on TiO2 materials is an interesting method for the tr... more ABSTRACT Heterogeneous photocatalysis based on TiO2 materials is an interesting method for the treatment of polluted water because it allows degradation of a wide variety of organic contaminant compounds. The performance of TiO2 based photocatalysts was studied by aqueous solutions of methylene blue (MB) as a model contaminant compound by using 50 mg L−1 as initial water contaminant concentration in order to compare the photocatalytic behaviour of TiO2 Degussa P25 and some synthesized photocatalysts by hydrothermal treatment (nanostructured TiO2 and metal-doped nanostructured TiO2 photocatalysts: nanostructured Co–TiO2, nanostructured Fe–TiO2 and nanostructured Mn–TiO2) under UV and visible light irradiation. Photocatalytic materials characterization was carried out by X-ray diffraction (XRD), transmission electron microscopy (TEM), nitrogen adsorption–desorption, mercury porosimetry, XPS and diffuse reflectance UV–vis spectra. An improvement of the photocatalytic activity has been observed when nanostructured and doped photocatalysts were used under visible light irradiation, concluding that the hydrothermal treatment produces a nanostructuration of commercial titania by the formation of nanoparticles, which results in a large decrease of average crystallite size of undoped and doped titania, and in an important increase of BET specific area and total pore area.
A pesar de que su presencia de un modo relevante en los medios de comunicación es relativamente r... more A pesar de que su presencia de un modo relevante en los medios de comunicación es relativamente reciente, las pilas de combustible se conocen desde hace más de 150 años. Los estudios pioneros de Schönbein y Grove dieron origen a la tecnología de pilas de combustible que es la que conocemos hoy en día. Posteriormente numerosos investigadores han ido aportando nuevas ideas en los campos de materiales, electroquímica, combustibles, ingeniería, etc..., para acabar definiendo los diferentes tipos de pilas que conocemos actualmente. Esta interacción entre numerosos campos de investigación, a menudo interdisciplinares, ha dado lugar en los últimos 15 años a un aumento considerable, tanto desde el punto de vista de los resultados producidos como de las inversiones a nivel privado y público. Parte de ese esfuerzo investigador e inversor viene motivado por el cambio climático y/o el agotamiento de las reservas de combustibles fósiles en los que se basa el modelo energético actual, lo que ha o...
Boletin de la Sociedad Espanola de Ceramica y Vidrio
The performance and the potential application of the cubic members of the La(4)Sr(n-4)Ti(n)O(3n+2... more The performance and the potential application of the cubic members of the La(4)Sr(n-4)Ti(n)O(3n+2) series of compounds, i.e. n≥12, prepared by solid state reaction are discussed. Although these phases can be indexed as cubic perovskites by XRD, there exists some oxygen beyond the ABO3 stoichiometry accommodated in linear defects reminiscent to the oxygen rich layers in La2Ti2O7. Fuel cell tests reveal that these materials exhibit moderate responses under hydrogen, but also some promising results implying activation favouring methane oxidation.
En este trabajo revisamos brevemente las pilas de combustible poliméricas (PEM) basadas en membra... more En este trabajo revisamos brevemente las pilas de combustible poliméricas (PEM) basadas en membranas de intercambio protónico y que constituyen la tecnología idónea de pilas de combustible de baja temperatura, y por tanto las más adecuadas para aplicación en transporte. Revisaremos los materiales que las componen pero también los desarrollos necesarios para su implantación definitiva en un mercado inclemente con las tecnologías caras, por limpias que sean. Palabras claves: pila de combustible, membrana polimérica, PEMFC, catalizador, electrolíto SUMMARY In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, which are the ideal technology for fuel cells at low temperature, and therefore more suitable for use in transportation. We will review the materials that compose them, but also the necessary developments for its final implementation in a market that it is not friendly with expensive technologies, even they are clean.
Afinidad -Barcelona-
In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, whic... more In this paper we briefly review polymer fuel cells (PEM) based on proton exchange membranes, which are the ideal technology for fuel cells at low temperature, and therefore more suitable for use in transportation. We will review the materials that compose them, but also the necessary developments for its final implementation in a market that it is not friendly with expensive technologies, even they are clean.
Solid State Ionics, 2005
A modified freeze-dried method has been used to obtain polycrystalline powders of the ionic condu... more A modified freeze-dried method has been used to obtain polycrystalline powders of the ionic conductor La2Mo2O9. Such ceramic powders were characterized by TG/DTA, XRD, SEM and TEM, and their sinterability was analysed by dilatometry and isothermal sintering ...
Fuel Cells, 2008
The layered perovskite GdBaCo 2 O 5 + d (GBCO), recently proposed for intermediate temperature so... more The layered perovskite GdBaCo 2 O 5 + d (GBCO), recently proposed for intermediate temperature solid oxide fuel cell applications, was investigated and compared with Ba 0.5 Sr 0.5 -Co 0.8 Fe 0.2 O 3d (BSCF) cathode material using La 0.9 A 0.1 -Ga 0.8 Mg 0.2 O 2.85 (A=Sr,Ba) as electrolytes. Area-specific resistance was measured by impendance spectroscopy in symmetrical cells. The cobaltites were prepared by a modified citrate sol-gel route and tested as cathode materials for doped lanthanum gallate-based cells using dry H 2 as fuel and air as oxidant, rendering power density values of 180 and 240 mW cm -2 at 1,073 K (1 mm thick pellets) for GBCO and BSCF fuel cells, respectively.
ChemInform, 2008
Preparation of Thin Layer Materials with Macroporous Microstructure for SOFC Applications. -Thin ... more Preparation of Thin Layer Materials with Macroporous Microstructure for SOFC Applications. -Thin layer oxide materials generally used in solid oxide fuel cells and catalytic applications with fluorite and perovskite-type structures such as doped zirconia, ceria, ferrites, manganites, and NiO-YSZ composites are prepared with controlled macroporous microstructure using polymethyl methacrylate microspheres as pore formers. The materials exhibit homogeneous pore distributions with relatively high specific surface areas between 11 and 38 m 2 /g after calcination between 450 and 650°C. The samples are characterized by XRD, SEM, TEM, nitrogen adsorption, and mercury porosimetry. These film materials possibly exhibit better performance for solid oxide fuel cell application in the intermediate temperature range than usual electrodes made of polycrystalline materials. -(MARRERO-LOPEZ, D.; RUIZ-MORALES, J. C.; PENA-MARTINEZ, J.; CANALES-VAZQUEZ, J.; NUNEZ*, P.; J. Solid State Chem. 181 (2008) 4, 685-692; Dep. Quim. Inorg., Univ.
Here we report two novel procedures that may lead to enhanced efficiencies of a SOFC via a precis... more Here we report two novel procedures that may lead to enhanced efficiencies of a SOFC via a precise control of the electrode microstructure and through the fabrication of a new type of electrolyte-supported SOFC. The first route is a simple and cost-effective method that ...
ABSTRACT Conference code: 69824, Export Date: 24 December 2012, Source: Scopus, CODEN: MRSPD, Lan... more ABSTRACT Conference code: 69824, Export Date: 24 December 2012, Source: Scopus, CODEN: MRSPD, Language of Original Document: English, Correspondence Address: Ruiz-Morales, J.C.; Department of Inorganic Chemistry, University of La Laguna, Avda. Astrofisico Fco. Sanchez, s/n, La Laguna, E-38200, Spain, References: Minh, N.Q., Takahashi, T., (1995) Science and Technology of Ceramic Fuel Cells, , Elsevier, Amsterdam;
ABSTRACT The characteristics of a solid oxide fuel cell cathode are investigated using a combinat... more ABSTRACT The characteristics of a solid oxide fuel cell cathode are investigated using a combination of scanning electron microscopy, electrochemical impedance spectroscopy and simulations using the state-space model (SSM). We successfully explain the shape of the impedance spectrum at several temperatures, determine kinetic parameters, measure the triple phase boundary length and deduce its width. Finally a quantitative analysis of the constant phase element using surface roughness and energy activation distribution is presented. © 2009 Elsevier B.V. All rights reserved.
Journal of the European Ceramic Society, 2013
Gd-doped ceria nanopowders have been synthesized via a modified sol-gel technique using different... more Gd-doped ceria nanopowders have been synthesized via a modified sol-gel technique using different pyrolysis temperatures to produce a range of particle sizes. Such nanocrystalline oxides have been sintered at 1400 • C for 24 h to produce fully dense disks. The microstructural characterization reveals that the pyrolysis temperature notably affects the grain size distribution in the sintered ceramics, e.g. powders treated at 700 • C render the narrowest grain size distribution. The electrochemical characterisation performed by electrochemical impedance spectroscopy shows that the distribution of grain sizes in the dense electrolytes rules the electrical conductivity of CGOs rather than the average grain size. Narrower grain size distributions render electrolytes exhibiting higher overall conductivity, independent of the average grain size.
A synthesis method based on freeze-dried precursors was used to obtain nanocrystalline powders of... more A synthesis method based on freeze-dried precursors was used to obtain nanocrystalline powders of pure and Ca-doped LaNbO 4 at 800 • C. Dense ceramics were prepared at temperature as low as 1100 • C. The LaNbO 4 ceramics were examined by scanning electron microscopy (SEM) to study the microstructure evolution with the sintering temperature. The densification and grain growth rate are lower in Ca-doped samples. The bulk and grain boundary contributions to the overall conductivity were studied by impedance spectroscopy under different gases. Samples sintered at low temperature and with smaller grain size exhibit higher grain boundary resistance and consequently lower total conductivity.