Transport properties and in-situ Raman spectroscopy study of BaCe 0.9 Y 0.1 O 3 - δ as a function of water partial pressures A. Grimaud a, ⁎, J.M. Bassat a , F. Mauvy a , P. Simon b , A. Canizares b,c , B. Rousseau b,c , M. Marrony d , J.C. Grenier a a CNRS, Université de Bordeaux, ICMCB, 87 avenue du Dr. A. Schweitzer, Pessac, F-33608, France b CNRS, UPR 3079 CEMHTI, 45071 Orléans Cedex 2, France c Université d'Orléans, 45067 Orléans Cedex 2, France d EIFER Emmy-Noether-Strasse 11, 76131 Karlsruhe, Germany abstract article info Article history: Received 15 February 2011 Received in revised form 17 March 2011 Accepted 30 March 2011 Available online 22 April 2011 Keywords: Proton conducting oxide Yttrium barium cerate Transport numbers Raman spectroscopy Defect structure The total conductivity of BaCe 0.9 Y 0.1 O 3 -δ material was measured under air, in a large p(H 2 O) range up to 0.30 bar. The defect concentrations (OH O · , V O ·· and h · ) and electrical conductivities were calculated on the basis of chemical constants (diffusion coefficients and equilibrium constants reported in the past literature) and compared to the experimental data. Protonic transport number as high as 0.8 was found at 700 °C, under air containing 0.30 bar of water, which allows a possible extension of the protonic temperature range of this material using water rich atmosphere. In-situ Raman spectroscopy under wet and dry air was performed from room temperature up to 700 °C in two wavenumber ranges. At low wavenumber, characteristic of lattice vibrations, this study clearly shows that no significant changes occur upon water insertion while at high wavenumbers, characteristic of OH vibrations, two contributions to the OH vibrations were found. This is discussed in terms of proton environment and transient hydrogen bonds. Moreover, this in situ study confirms that, at moderate p(H 2 O), water insertion becomes significant at temperature below 650 °C. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Proton conducting ceramics are of great interest for many applications such as hydrogen gas sensors, hydrogen pumps and solid electrolytes for fuel cells [1]. Except new materials such as the ortho- niobates (as LaNbO 4 [2]) or mixed perovskites (as Ba 3 Ca 1.18 Nb 1.82 O 9 [3]), the most studied proton conducting oxides remain the perovskite family. Among them, zirconate and cerate-based compounds are the most widely studied. BaCeO 3 -based materials exhibit quite high ionic conductivity (σ ≥ 10 -2 S.cm -1 at T=600 °C) and are considered as potential electrolyte materials for proton conducting Solid Oxide Fuel Cell (H + -SOFC). Indeed, the protonic conductivity in these materials results from water insertion into the oxide network, leading to the formation of hydroxyl species according to the reaction: AMO 3-δ + x 2 H 2 O→AMO 3-δ- x 2 OH ð Þ x : ð1Þ On the other hand, their conductivity behavior as a function of oxygen partial pressure p(O 2 ) has been described by three different transport property regimes: under high and low p(O 2 ), p-type and n-type electronic conductivities are present, respectively, whereas at intermediate p(O 2 ) (10 -5 bar ≤ p(O 2 ) ≥ 10 -20 bar) conductivity is pure- ly ionic (H + and O 2- ) [4–6]. Thus, the issue of major mobile ionic species has been widely studied and proton conduction appears to be predominant at temperature below 600 °C while oxygen conduction strongly increases at temperature above 600 °C, due to dehydration of these oxides. From a general point of view, proton mobility in oxides, and especially in substituted BaCeO 3 , is dependent on the strength of hydrogen bonds with the next-nearest oxygen atoms [7,8]. This hydrogen bond strength can be characterized thanks to the OH vibration broad band observable at wavenumbers below 3600 cm -1 in infrared (IR) absorption spectra [9,10]. For several proton conducting oxides, wavenumbers of the fundamental OH vibration as low as 2500 cm -1 were found due to the low-wavenumber shifting of OH vibration of strong bonds [11–13]. In addition to IR studies, Raman spectroscopy may also bring some new information concerned with the modification of lattice vibrations by water insertion into oxide networks. As IR and Raman active modes are different, both approaches are complementary, whatever the considered wavenumber range. The first part of this paper is devoted to the study of the BaCe 0.9 Y 0.1 O 3 - δ (BCY10) conductivity as a function of water partial pressure p(H 2 O) in the range of 0.03 to 0.30 bar, which had never been explored till now. Actually, most previous papers focused on the dependence of the conductivity on p(O 2 ) at low p(H 2 O) and there Solid State Ionics 191 (2011) 24–31 ⁎ Corresponding author. E-mail address: grimaud@icmcb-bordeaux.cnrs.fr (A. Grimaud). 0167-2738/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2011.03.020 Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi