Dry-sliding wear behavior of 3Y-TZP/Al2O3-NbC nanocomposites produced by conventional sintering and spark plasma sintering

[EN] This work presents the initial results of the dry-sliding wear behavior of 3 mol% yttria-stabilized zirconia reinforced with 5 vol% alumina-niobium carbide (3Y-TZP/5 vol% Al2O3-NbC) nanocomposites sintered by conventional sintering and spark plasma sintering methods in the temperature range of 1350-1450 degrees C. The reinforcement of 3Y-TZP matrix with hard nanoparticles aimed to improve wear strength of the composites. Wear tests were performed by the ball-on-disc method using alumina (Al2O3) and tungsten carbide with 6 wt% cobalt cermet (WC-6%Co) balls as counter-materials, a load of 15 N, a sliding distance of 2000 m, and a sliding speed of 0.1 m/s. Wear behavior was evaluated in terms of wear rate and FE-SEM micrograph analysis of the wear tracks. The nanocomposite sintered at 1450 degrees C by conventional sintering exhibited the least wear when tested with the WC-6%Co ball. Generally, the wear mechanism showed evidence of severe wear regime with both counter-materials.The authors acknowledge the Brazilian institutions CAPES-PVE (grant number 23038.009604/2013-12), FAPESP (grant number 2015/07319-8), Fundação Araucária (grant number 810/2014), European Union/Erasmus Mundus for doctorate mobility (grant number EB15DM1542), and the Spanish Ministry of Economy and Competitiveness (RYC-2016-20915).Salem, R.; Gutiérrez-González, C.; Borrell Tomás, MA.; Salvador Moya, MD.; Chinelatto, AL.; Chinelatto, AS.; Pallone, E. (2019). Dry-sliding wear behavior of 3Y-TZP/Al2O3-NbC nanocomposites produced by conventional sintering and spark plasma sintering. International Journal of Applied Ceramic Technology. 16(3):1265-1273. https://doi.org/10.1111/ijac.13151S12651273163Liu, H., Zhao, W., Ji, Y., Cui, J., Chu, Y., & Rao, P. (2017). Determination of fracture toughness of zirconia ceramics with different yttria concentrations by SEVNB method. Ceramics International, 43(13), 10572-10575. doi:10.1016/j.ceramint.2017.04.064Ćorić, D., Majić Renjo, M., & Ćurković, L. (2017). Vickers indentation fracture toughness of Y-TZP dental ceramics. International Journal of Refractory Metals and Hard Materials, 64, 14-19. doi:10.1016/j.ijrmhm.2016.12.016De Aza, A. H., Chevalier, J., Fantozzi, G., Schehl, M., & Torrecillas, R. (2002). Crack growth resistance of alumina, zirconia and zirconia toughened alumina ceramics for joint prostheses. Biomaterials, 23(3), 937-945. doi:10.1016/s0142-9612(01)00206-xAragón-Duarte, M. C., Nevarez-Rascón, A., Esparza-Ponce, H. E., Nevarez-Rascón, M. M., Talamantes, R. P., Ornelas, C., … Hurtado-Macías, A. (2017). Nanomechanical properties of zirconia- yttria and alumina zirconia- yttria biomedical ceramics, subjected to low temperature aging. Ceramics International, 43(5), 3931-3939. doi:10.1016/j.ceramint.2016.12.033Balko, J., Csanádi, T., Sedlák, R., Vojtko, M., KovalĿíková, A., Koval, K., … Naughton-Duszová, A. (2017). Nanoindentation and tribology of VC, NbC and ZrC refractory carbides. Journal of the European Ceramic Society, 37(14), 4371-4377. doi:10.1016/j.jeurceramsoc.2017.04.064Alecrim, L. R. R., Ferreira, J. A., Gutiérrez-González, C. F., Salvador, M. D., Borrell, A., & Pallone, E. M. J. A. (2017). Effect of reinforcement NbC phase on the mechanical properties of Al2O3-NbC nanocomposites obtained by spark plasma sintering. International Journal of Refractory Metals and Hard Materials, 64, 255-260. doi:10.1016/j.ijrmhm.2016.10.021Alecrim, L. R. R., Ferreira, J. A., Gutiérrez-González, C. F., Salvador, M. D., Borrell, A., & Pallone, E. M. J. A. (2017). Sliding wear behavior of Al2O3-NbC composites obtained by conventional and nonconventional techniques. Tribology International, 110, 216-221. doi:10.1016/j.triboint.2017.02.028Santos, C., Maeda, L. D., Cairo, C. A. A., & Acchar, W. (2008). Mechanical properties of hot-pressed ZrO2–NbC ceramic composites. International Journal of Refractory Metals and Hard Materials, 26(1), 14-18. doi:10.1016/j.ijrmhm.2007.01.008Ünal, N., Kern, F., Öveçoğlu, M. L., & Gadow, R. (2011). Influence of WC particles on the microstructural and mechanical properties of 3mol% Y2O3 stabilized ZrO2 matrix composites produced by hot pressing. Journal of the European Ceramic Society, 31(13), 2267-2275. doi:10.1016/j.jeurceramsoc.2011.05.032Sequeira, S., Fernandes, M. H., Neves, N., & Almeida, M. M. (2017). Development and characterization of zirconia–alumina composites for orthopedic implants. Ceramics International, 43(1), 693-703. doi:10.1016/j.ceramint.2016.09.216Schmitt-Radloff, U., Kern, F., & Gadow, R. (2017). Wire-electrical discharge machinable alumina zirconia niobium carbide composites – Influence of NbC content. Journal of the European Ceramic Society, 37(15), 4861-4867. doi:10.1016/j.jeurceramsoc.2017.07.014Akatsu, T., Nakanishi, S., Tanabe, Y., Wakai, F., & Yasuda, E. (2013). Toughening enhanced at elevated temperatures in an alumina/zirconia dual-phase matrix composite reinforced with silicon carbide whiskers. Journal of the European Ceramic Society, 33(15-16), 3157-3163. doi:10.1016/j.jeurceramsoc.2013.05.029Lee, D.-J., Choi, H.-S., Jin, F.-L., & Park, S.-J. (2015). A study on mechanical properties and microstructure of tetragonal zirconia-based composites. Journal of Industrial and Engineering Chemistry, 27, 322-328. doi:10.1016/j.jiec.2015.01.008Salem, R. E. P., Monteiro, F. R., Gutiérrez-González, C. F., Borrell, A., Salvador, M. D., Chinelatto, A. S. A., … Pallone, E. M. J. A. (2018). Effect of Al2O3-NbC nanopowder incorporation on the mechanical properties of 3Y-TZP/Al2O3-NbC nanocomposites obtained by conventional and spark plasma sintering. Ceramics International, 44(2), 2504-2509. doi:10.1016/j.ceramint.2017.10.235Schmitt-Radloff, U., Kern, F., & Gadow, R. (2018). Spark plasma sintering and hot pressing of ZTA-NbC materials – A comparison of mechanical and electrical properties. Journal of the European Ceramic Society, 38(11), 4003-4013. doi:10.1016/j.jeurceramsoc.2018.04.022Pędzich, Z., Haberko, K., Faryna, M., & Sztwiertnia, K. (2002). Interphase Boundary in Zirconia – Carbide Particulate Composites. Key Engineering Materials, 223, 221-226. doi:10.4028/www.scientific.net/kem.223.221Acchar, W., Zollfrank, C., & Greil, P. (2004). Microstructure and mechanical properties of WC-Co reinforced with NbC. Materials Research, 7(3), 445-450. doi:10.1590/s1516-14392004000300012Guillon, O., Gonzalez‐Julian, J., Dargatz, B., Kessel, T., Schierning, G., Räthel, J., & Herrmann, M. (2014). Field‐Assisted Sintering Technology/Spark Plasma Sintering: Mechanisms, Materials, and Technology Developments. Advanced Engineering Materials, 16(7), 830-849. doi:10.1002/adem.201300409Munir, Z. A., Anselmi-Tamburini, U., & Ohyanagi, M. (2006). The effect of electric field and pressure on the synthesis and consolidation of materials: A review of the spark plasma sintering method. Journal of Materials Science, 41(3), 763-777. doi:10.1007/s10853-006-6555-2Lu, K. (2008). Sintering of nanoceramics. International Materials Reviews, 53(1), 21-38. doi:10.1179/174328008x254358Borrell, A., Fernández, A., Torrecillas, R., Córdoba, J. M., Avilés, M. A., & Gotor, F. J. (2010). Spark Plasma Sintering of Ultrafine TiCxN1−x Powders Synthesized by a Mechanically Induced Self-Sustaining Reaction. Journal of the American Ceramic Society, 93(8), 2252-2256. doi:10.1111/j.1551-2916.2010.03735.xBonache, V., Salvador, M. D., Fernández, A., & Borrell, A. (2011). Fabrication of full density near-nanostructured cemented carbides by combination of VC/Cr3C2 addition and consolidation by SPS and HIP technologies. International Journal of Refractory Metals and Hard Materials, 29(2), 202-208. doi:10.1016/j.ijrmhm.2010.10.007Gutiérrez-Mora, F., Cano-Crespo, R., Rincón, A., Moreno, R., & Domínguez-Rodríguez, A. (2017). Friction and wear behavior of alumina-based graphene and CNFs composites. Journal of the European Ceramic Society, 37(12), 3805-3812. doi:10.1016/j.jeurceramsoc.2017.02.024Wei, J., Lin, B., Wang, H., Sui, T., Yan, S., Zhao, F., … Fang, S. (2018). Friction and wear characteristics of carbon fiber reinforced silicon carbide ceramic matrix (Cf/SiC) composite and zirconia (ZrO2) ceramic under dry condition. Tribology International, 119, 45-54. doi:10.1016/j.triboint.2017.10.023Fan, H., Hu, T., Zhang, Y., Fang, Y., Song, J., & Hu, L. (2014). Tribological properties of micro-textured surfaces of ZTA ceramic nanocomposites under the combined effect of test conditions and environments. Tribology International, 78, 134-141. doi:10.1016/j.triboint.2014.05.010Gee, M., & Nunn, J. (2017). Real time measurement of wear and surface damage in the sliding wear of alumina. Wear, 376-377, 1866-1876. doi:10.1016/j.wear.2017.01.114Wang, Y., Yang, Y., Zhao, Y., Tian, W., Bian, H., & He, J. (2009). Sliding wear behaviors of in situ alumina/aluminum titanate ceramic composites. Wear, 266(11-12), 1051-1057. doi:10.1016/j.wear.2008.11.006Krell, A. (1996). Improved hardness and hierarchic influences on wear in submicron sintered alumina. Materials Science and Engineering: A, 209(1-2), 156-163. doi:10.1016/0921-5093(95)10155-1Botta F, W. ., Tomasi, R., Pallone, E. M. J. ., & Yavari, A. . (2001). Nanostructured composites obtained by reactive milling. Scripta Materialia, 44(8-9), 1735-1740. doi:10.1016/s1359-6462(01)00789-8Pallone, E. M. J. ., Trombini, V., Botta F, W. ., & Tomasi, R. (2003). Synthesis of Al2O3–NbC by reactive milling and production of nanocomposites. Journal of Materials Processing Technology, 143-144, 185-190. doi:10.1016/s0924-0136(03)00411-4ASTM G99‐03 Standard test method for wear testing with a pin‐on‐disc apparatus ASTM Annual Book of Standards vol.03. West Conshohocken PA;2003.Chen, W.-H., Lin, H.-T., Chen, J., Nayak, P. K., Lee, A. C., Lu, H.-H., & Huang, J.-L. (2016). Microstructure and wear behavior of spark plasma sintering sintered Al2O3/WC-based composite. International Journal of Refractory Metals and Hard Materials, 54, 279-283. doi:10.1016/j.ijrmhm.2015.07.030Espinosa-Fernández, L., Borrell, A., Salvador, M. D., & Gutierrez-Gonzalez, C. F. (2013). Sliding wear behavior of WC–Co–Cr3C2–VC composites fabricated by conventional and non-conventional techniques. Wear, 307(1-2), 60-67. doi:10.1016/j.wear.2013.08.003Bundschuh, W., & Gahr, K.-H. Z. (1991). Influence of porosity on friction and sliding wear of tetragonal zirconia polycrystal. Wear, 151(1), 175-191. doi:10.1016/0043-1648(91)90356-yBayer, R. J. (2004). Mechanical Wear Fundamentals and Testing, Revised and Expanded. doi:10.1201/9780203021798Zum Gahr, K.-H. (1989). Sliding wear of ceramic-ceramic, ceramic-steel and steel-steel pairs in lubricated and unlubricated contact. Wear, 133(1), 1-22. doi:10.1016/0043-1648(89)90109-9Kato, K., & Adachi, K. (2002). Wear of advanced ceramics. Wear, 253(11-12), 1097-1104. doi:10.1016/s0043-1648(02)00240-5Pasaribu, H. R., Sloetjes, J. W., & Schipper, D. J. (2004). The transition of mild to severe wear of ceramics. Wear, 256(6), 585-591. doi:10.1016/j.wear.2003.10.025Wang, S. W., Chen, L. D., Hirai, T., & Kang, Y. S. (1999). Journal of Materials Science Letters, 18(14), 1119-1121. doi:10.1023/a:1006684631127Muñoz, S., & Anselmi-Tamburini, U. (2012). Parametric investigation of temperature distribution in field activated sintering apparatus. The International Journal of Advanced Manufacturing Technology, 65(1-4), 127-140. doi:10.1007/s00170-012-4155-7Xiong, Y., Fu, Z. Y., Wang, H., Wang, Y. C., & Zhang, Q. J. (2005). Microstructure and IR transmittance of spark plasma sintering translucent AlN ceramics with CaF2 additive. Materials Science and Engineering: B, 123(1), 57-62. doi:10.1016/j.mseb.2005.06.02

Phase Transitions, Chemical Expansion, and Deuteron Sites in the BaZr 0.7 Ce 0.2 Y 0.1 O 3−δ Proton Conductor

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; EspañaFil: Heras Juaristi, Gemma. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Ritter, Clemens. Institut Laue Langevin; FranciaFil: Fuentes, Rodolfo Oscar. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Chinelatto, Adilson L.. Universidade Estadual de Ponta Grossa; BrasilFil: Pérez Coll, Domingo. Instituto de Ceramica y Vidrio de Madrid; EspañaFil: Amador, Ulises. Universidad CEU San Pablo; Españ

Protonic and electronic defects in the 12R-type hexagonal perovskite Sr3LaNb3O12

The structural properties of the 12R-type hexagonal perovskite Sr 3LaNb3O12 (space group R3̄) have been examined by neutron diffraction and 1H magic angle spinning-nuclear magnetic resonance (1H MAS-NMR). The latter technique supports the presence of protonic species in Sr3LaNb3O12 with bands at 5, 3.4 and 1.3 ppm. The electrical-transport properties of the nominally stoichiometric and acceptor-doped phases Sr3LaNb 3 - xMxO12 - δ (M = Ti, x = 0.1; M = Zr, x = 0.03) have been analysed in the temperature range 550-900 C by impedance spectroscopy in a selection of wet- and dry-gas atmospheres. Protons contribute increasingly to transport with decreasing temperature in wet air, as confirmed by an H+/D+ isotope effect, representing the first observation of proton conductivity in this structure type. The magnitude of the protonic transport increases with increasing acceptor-dopant concentration (x). A total conductivity value of 1.2 × 10- 6 S cm- 1 is reached at 650 C for the Ti-doped phase in humidified air (pH2O ≈ 0.03 atm). The activation energy in wet air at 550-700 C is slightly lower for the doped compositions (0.93 eV for the Zr-doped phase) in comparison to the nominally undoped material (1.13 eV). The origin of proton transport in the latter may originate from >self doping> of a small amount of Sr on the La sites. Conductivity is dominated by n-type charge carriers in reducing conditions, as confirmed by the observance of a - 1/4 power-law dependency for pO2 ≤ ~ 10- 8 atm. The activation energy of the title phase in the n-type region measured in 10% H2:90% N2 is 0.96 eV. In dry oxidising atmospheres, p-type charge carriers predominate (Ea = 1.42 eV) with the p-n transition occurring at pO2 ~ 10- 4 atm. © 2013 Elsevier B.V.We thank the MINECO (ENE2012-30929) and the EU (ROBANODE, FP7-FCH-JU-2008-1-CP) for financial assistance. D. Pérez-Coll and A Thursfield also acknowledge the financial support of a “Ramón y Cajal” contract (MINECO, CSIC) and of the EPSRC (EP/G012865/1), respectively.Peer Reviewe

Structures, Phase Fields, and Mixed Protonic-Electronic Conductivity of Ba-Deficient, Pr-Substituted BaZr0.7Ce0.2Y0.1O3-δ

[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

Structures, phase fields, and mixed protonic−electronic conductivity of Ba-Deficient, Pr-Substituted BaZr0.7Ce0.2Y0.1O3−δ

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.The BaZr0.7Ce0.2Y0.1O3−δ−BaPrO3−δ perovskite system, of interest for high-temperature electrochemical applications involving mixed protonic−electronic conductivity, forms a solidsolution with a wide interval of Ba substoichiometry in the range Ba(Ce0.2Zr0.7)1−xPrxY0.1O3−δ, 0 ≤ x ≤ 1. Structural phase transitions mapped as a function of temperature and composition by highresolution 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, R3̅c). 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−1 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 (N2) and at low Pr contents, conductivity is higher in humidified atmospheres (∼0.023 atm pH2O) indicating a protonic contribution to transport, whereas the greater electron−hole conductivity with increasing Pr content results in lower conductivity in humidified N2 due to the creation of protonic defects and the consumption of holes.MINECOCAPES, BrazilDepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

Thermal evolution of structures and conductivity of Pr-substituted BaZr0.7Ce0.2Y0.1O3-delta: potential cathode components for protonic ceramic fuel cells

The authors would like to congratulate Professor Tony West on the occasion of his 70th birthday. GCM especially appreciates the invaluable guidance in solid-state chemistry provided to him by Prof. West. This work was supported by the MINECO, Spain (ENE2015-66183-R, MAT2016-78362-C4-1-R), CSIC, Spain (i-link0743), CAPES, Brazil (PVE, Proceso 88881.03418/2013-1) and the FCT, Portugal (POPH, PTDC CTM-EME 6319 2014). 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. U. A. also thanks the Universidad San Pablo for financial support.A complete solid solution forms between the perovskite proton conductor BaZr0.7Ce0.2Y0.1O3 d (BZCY72) and BaPr0.9Y0.1O3-d (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-d series were studied as a function of composition and temperature by high-resolution neutron powder diffraction revealing symmetry changes in the sequence Pnma / Imma / R3c / Pm-3m. 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 near 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 near 1 eV for BZCY72 to near 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.MINECO, SpainCAPES, BrazilFCT, PortugalNational Synchrotron Light LaboratoryDepto. de Química InorgánicaFac. de Ciencias QuímicasTRUEpu

Structures, Phase Fields, and Mixed Protonic-Electronic Conductivity of Ba-Deficient, Pr-Substituted BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ

The BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ -BaPrO 3-δ 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(Ce 0.2 Zr 0.7 ) 1-x Pr x Y 0.1 O 3-δ , 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 -1 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 2 ) and at low Pr contents, conductivity is higher in humidified atmospheres (0.023 atm pH 2 O) indicating a protonic contribution to transport, whereas the greater electron-hole conductivity with increasing Pr content results in lower conductivity in humidified N 2 due to the creation of protonic defects and the consumption of holes.Fil: Heras Juaristi, Gemma. Instituto de Ceramica y Vidrio de Madrid; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Amador, Ulises. Universidad CEU-San Pablo; EspañaFil: Romero de Paz, Julio. Universidad Complutense de Madrid; EspañaFil: Fuentes, Rodolfo Oscar. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Chinelatto, Adilson L.. Universidade Estadual de Ponta Grossa; BrasilFil: Ritter, Clemens. Institut Laue-Langevin; FranciaFil: Fagg, Duncan P.. Universidad de Aveiro; PortugalFil: Pérez Coll, Domingo. Instituto de Cerámica y Vidrio de Madrid; España. Consejo Superior de Investigaciones Científicas; EspañaFil: Mather, Glenn C.. Instituto de Cerámica y Vidrio de Madrid; España. Consejo Superior de Investigaciones Científicas; Españ