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[EN] The BaZrCeYO-BaPrO perovskite system, of interest for high-temperature electrochemical applications involving mixed protonic-electronic conductivity, forms a solid-solution with a wide interval of Ba substoichiometry in the range Ba(CeZr)PrYO, 0 ≤ x ≤ 1. Structural phase transitions mapped as a function of temperature and composition by high-resolution neutron powder diffraction and synchrotron X-ray diffraction reveal higher symmetry for lower Pr content and higher temperatures, with the largest stability field observed for rhombohedral symmetry (space group, R3c). Rietveld refinement, supported by magnetic-susceptibility measurements, indicates that partitioning of the B-site cations over the A and B perovskite sites compensates Ba substoichiometry in preference to A-site vacancy formation and that multiple cations are distributed over both sites. Electron-hole transport dominates electrical conductivity in both wet and dry oxidizing conditions, with total conductivity reaching a value of 0.5 S cm for the x = 1 end-member in dry air at 1173 K. Higher electrical conductivity and the displacement of oxygen loss to higher temperatures with increasing Pr content both reflect the role of Pr in promoting hole formation at the expense of oxygen vacancies. In more reducing conditions (N) and at low Pr contents, conductivity is higher in humidified atmospheres (0.023 atm pHO) indicating a protonic contribution to transport, whereas the greater electron-hole conductivity with increasing Pr content results in lower conductivity in humidified N due to the creation of protonic defects and the consumption of holes., We thank the MINECO, Spain (ENE2015-66183-R and MAT2016-78362-C4-1-R), CSIC, Spain (i-link0743), and CAPES, Brazil (PVE, Proceso 88881.03418/2013-1). Access to the neutron facilities at the Institut Laue Langevin (Grenoble, France) and the National Synchrotron Light Laboratory (LNLS, Campinas, Brazil) under grant 5-24-55(D2B) and research proposal D10B-XRD1-16166, respectively, is gratefully acknowledged. We also thank the FCT, PTDC/CTM-EME/6319/2014, QREN, FEDER, and COMPETE Portugal and the European Social Fund, European Union. U.A. acknowledges the Universidad San Pablo for financial support. We would also like to thank Steven Kermorvant and Alexandre Bosser of the IUT, University of Rennes (France), for assistance.

A complete solid solution forms between the perovskite proton conductor BaZr0.7Ce0.2Y0.1O3-δ (BZCY72) and BaPr0.9Y0.1O3-δ (BPY) on synthesis by the Pechini method and high-temperature annealing. Phase fields of selected members of the Ba(Zr0.7Ce0.2)1-(x/0.9)PrxY0.1O3-δ series were studied as a function of composition and temperature by high-resolution neutron powder diffraction revealing symmetry changes in the sequence Pnma → Imma → → Pm3m. Higher symmetry is favoured for low Pr contents and high temperatures, as consideration of tolerance factor suggests. A volume contraction, ascribed to dehydration, is observed by synchrotron X-ray diffraction on heating in air for lower x. Magnetic measurements and structural data support the presence of Pr in the IV valence state on the perovskite B site. Thermogravimetric analysis in CO2 to ∼1253 K indicates better chemical stability for x ≤ 0.445, whereas decomposition occurred for higher x. Electrical conductivity increases by over two orders of magnitude in dry air at lower temperature from x = 0.225 to 0.675; total conductivity reaches a value of 0.4 S cm-1 at 1173 K for x = 0.675. The series exhibits electron-hole transport with a positive pO2 dependence which increases with temperature, consistent with participation of oxygen vacancies in charge compensation of the Y3+ acceptor dopant. The activation energy for thermally activated hole hopping in air in the range 523-773 K decreases from ∼1 eV for BZCY72 to ∼0.4 eV for x = 0.675. Conductivity is generally lower in humidified N2 and air (pH2O ≈ 0.023 atm) than the corresponding dry atmospheres, consistent with consumption of holes by less mobile protonic species; however for x ≤ 0.225 the lower concentration of electron holes concomitant with higher oxygen-vacancy content in N2 results in slightly higher conductivity in wet conditions due to hydration of vacancies. Fil: Heras Juaristi, Gemma. Instituto de Cerámica y Vidrio de Madrid; España Fil: Amador, Ulises. Universidad San Pablo Ceu; España Fil: Fuentes, Rodolfo Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Comisión Nacional de Energía Atómica; Argentina Fil: Chinelatto, Adilson L.. Universidade Estadual de Ponta Grossa; Brasil Fil: Romero De Paz, Julio. Universidad Complutense de Madrid; España Fil: Ritter, Clemens. Institut Laue Langevin; Francia Fil: Fagg, Duncan P.. Universidade de Aveiro; Portugal Fil: Pérez Coll, Domingo. Instituto de Cerámica y Vidrio de Madrid; España Fil: Mather, Glenn C.. Instituto de Cerámica y Vidrio de Madrid; España

The effects of sintering temperature and addition of 4 mol.% ZnO as sintering additive on the crystal structure, microstructure and electrical properties of SrZr 0.9 Y 0.1 O 3-δ are reported. The presence of ZnO as sintering aid brings about high densification at 1300 °C (relative density ∼97%); gas-tightness is not achieved for ZnO-free samples sintered below 1600 °C. Bulk conductivity (σ B ) is considerably higher in wet and dry O 2 on doping with ZnO, but only slight variations of σ B with sintering temperature are observed for the Zn-containing phases. Similarly, the apparent grain-boundary conductivities are much greater for the Zn-doped samples. The grain-boundary volume and accompanying resistances are much reduced on sintering at 1500 °C with ZnO addition in comparison to Zn-modified samples sintered below 1500 °C, with only minor changes in grain-boundary relaxation frequency observed. Conversely, in comparison to the undoped sample with sintering temperature of 1600 °C, there is an enormous improvement in the specific grain-boundary conductivity of two orders of magnitude for the ZnO-containing samples. Analysis on the basis of the core space-charge-layer model relates the enhancement of the grain-boundary transport to a higher concentration of charge carriers in the space-charge layer and associated lower potential barrier heights.

The BaZr

The crystal structure of the technologically relevant, high-temperature proton conductor BaZr0.7Ce0.2Y0.1O3−δ (BZCY72) has been studied by high-resolution neutron powder diffraction performed on a deuterated sample in the temperature range 10–1173 K, complemented with synchrotron X-ray diffraction in the range RT-1173 K. A volume discontinuity on heating indicates a first-order phase transition from orthorhombic (space group Imma) to rhombohedral symmetry (R3̅c) between 85 and 150 K. A further transition to cubic symmetry (Pm3̅m) takes place at ∼570 K, indicated to be second order from the temperature dependence of the octahedral tilt angle. The stability field of the cubic phase was extended on cooling in the dehydrated state to 85 K. Expansion/contraction of the unit-cell volume on heating in low vacuum and air, respectively observed by neutron diffraction and synchrotron X-ray diffraction, was described with a point-defect model involving the temperature dependence of the water content and thermal expansion. Isotropic strain in the hydrated state is apparent on analysis of the broadening of the neutron-diffraction reflections during heating and cooling cycles. Rietveld refinement of the low-temperature neutron data and Fourier nuclear-density maps were employed to locate the deuterium position at a distance of ∼0.90 Å from the bonding oxygen at 10 K. Fil: Mather, Glenn C.. Instituto de Ceramica y Vidrio de Madrid; España Fil: Heras Juaristi, Gemma. Instituto de Ceramica y Vidrio de Madrid; España Fil: Ritter, Clemens. Institut Laue Langevin; Francia Fil: Fuentes, Rodolfo Oscar. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Chinelatto, Adilson L.. Universidade Estadual de Ponta Grossa; Brasil Fil: Pérez Coll, Domingo. Instituto de Ceramica y Vidrio de Madrid; España Fil: Amador, Ulises. Universidad CEU San Pablo; España

[EN] Partial conductivities are presented for BaZrCeYO, an important proton conductor for protonic-ceramic fuel cells and membrane reactors. Atmospheric dependencies of impedance performed in humidified and dry O, air, N and H(10%)/N(90%) in the temperature range 300–900 °C, supported by the modified emf method, confirm significant electron-hole and protonic contributions to transport. For very reducing and wet atmospheres, the conductivity is predominantly ionic, with a higher participation of protons with decreasing temperature and increasing water-vapour partial pressure (pHO). From moderately reducing conditions of wet N to wet O, however, the conductivity is considerably influenced by electron holes as revealed by a significant dependence of total conductivity on oxygen partial pressure (pO). With higher pHO, proton transport increases, with a concomitant decrease of holes and oxygen vacancies. However, the effect of pHO is also influenced by temperature, with a greater protonic contribution at both lower temperature and pO. Values of proton transport number t ≈ 0.63 and electronic transport number t ≈ 0.37 are obtained at 600 °C for pHO = 0.022 atm and pO = 0.2 atm, whereas t ≈ 0.95 and t ≈ 0.05 for pO = 10 atm. A hydration enthalpy of −109 kJ mol is obtained in the range 600–900 °C., We thank the “Ministerio de Economía, Industria y Competitividad” (MINECO) in Spain for financial assistance (ENE2015-66183-R).

[EN] The mixed ionic-electronic transport properties of the protonic ceramic electrolyser material SrZr0.9Y0.1O3-, with the addition of 4mol% ZnO as sintering additive, are analysed under reducing conditions. The study is performed by means of an active-load modification of the classical electromotive-force method to account for the non-negligible effect of the electrodes on the obtained electrical-transport numbers. The methodology is developed in detail in order to link the electrochemical criteria to simulated equivalent circuits. The observed electromotive force of the system is considerably affected by the introduction of the polarisation resistance of the electrodes in the corresponding analysis, resulting in a high deviation between the present results and those obtained by a classical analysis without attending to electrode effects. Under wet reducing conditions (pH2  0.05 atm, pH2O 3·103102 atm), the oxide-ionic transport number is negligible in the range of 600900 ºC, whereas pure protonic conductivity is observed for temperatures ≤ 700 ºC and pH2O ≥ 5.6x103 atm. For higher temperatures and/or lower pH2O, mixed protonic-electronic conduction is exhibited. The electronic contribution under reducing conditions is consistent with n-type electronic behaviour., The authors acknowledge the financial support of MINECO (Plan Nacional, ENE2012-30929) and CSIC (i-link0743). We are grateful to Dr. M.J. Pascual (ICV, CSIC) for supplying the glass-ceramic seal.

[EN] Analysis of transport numbers is critical for assessing the suitability of an ion-conducting material for a given electrochemical application and the conditions for its employment. In this work, the proton, oxide-ion and electron transport numbers of the candidate protonic ceramic electrolyser and fuel cell material SrZr0.9Y0.1O3-δ (with the addition of 4 mol% ZnO as sintering aid) are measured in wet and dry oxidising atmospheres in the temperature range 700-850 C. The determination of proton transport numbers is analysed in detail, encompassing the suitability of equivalent circuits in different conditions and the inclusion of an external parallel resistance for the correction of electrode-polarisation effects (Gorelov method). It is confirmed that transport numbers are highly inaccurate if no polarisation correction is applied. In dry oxidising conditions oxide-ion transport numbers, to, lie in the range 0.63-0.78. The conductivity in wet oxidising conditions is dominated by protons and an electronic component, with the proton transport number increasing from 0.79 to 0.88 with increasing pH2O in the range 1.1 × 10-3 ≤ pH2O ≤ 1.27 × 10-2 atm at 700 C. © 2013 Elsevier B.V. All rights reserved., We thank the“Ministerio de Economía y Competitividad”(MINECO) (Plan Nacional, ENE2012-30929) forfinancial assistance.D. Pérez-Coll also acknowledges the support of a“Ramón y Cajal”contract (MINECO, CSIC). We are grateful to Dr M.J. Pascual (ICV,CSIC) for supplying the sealing glasseceramic