Structural modifications induced by free protons in proton conducting perovskite zirconate membrane Aneta Slodczyk a, ⁎, Philippe Colomban a , Gilles André b , Oumaya Zaafrani a , Frédéric Grasset c , Olivier Lacroix c , Béatrice Sala c a LADIR UMR7075 CNRS, UPMC, 4 Place Jussieu, 75005 Paris, France b Laboratoire Léon Brillouin CNRS-CEA, CEA Saclay, 91191 Gif-sur-Yvette, France c AREVA NP, Université Montpellier 2, Montpellier, 34095, France abstract article info Article history: Received 26 August 2011 Received in revised form 5 January 2012 Accepted 16 January 2012 Available online 9 February 2012 Keywords: Proton conductor Perovskite Ceramic Neutron diffraction In situ Raman scattering Recently hydrogen appears as an alternative energy vector for a sustainable modern world. Proton conduct- ing perovskite ceramics showing significant proton conduction (~ 10 -2 S/cm at 600 °C) at medium tempera- ture exhibit high potential as electrolytic membranes of water steam electrolysers. Prior to industrial requirements (mechanical and chemical stability, long working life) the structural behaviour of the host pe- rovskite structure disturbed by the Ln/RE substitution and the presence of protonic species have to be well determined as a function of severe operating conditions. Ex situ neutron diffraction and thermal expansion as well as in situ high water pressure Raman studies were performed on non-protonated, protonated and deprotonated high dense SrZr 0.9 Yb 0.1 O 2.95 ceramics. The results show that the proton doping (SrZr 0.9 Yb 0.1- O 2.95 H 0.003 ) induces long range order structural modifications, weak enough to guaranty the stability during the high water pressure–high temperature cycling. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Water electrolysis based on the proton conduction can assure a low cost and environment friendly (CO 2 free) production of hydrogen [1–3]. Proton conducting perovskite ceramics with a general formula A 2+ (Ba, Sr, etc.) B 4+ (Zr, Ce, Ti, Nb etc.) O 3 appear as convenient materials for elec- trolytic membranes of water steam electrolysers. Prior to a successful industrial application, such membranes should be chemically and me- chanically stable under severe operating conditions. It should be stressed that the presence of abrupt, discontinuous phase transitions as well as of important variations of a unit-cell volume can lead to mechanical insta- bility. Since the presence of protons is not intrinsic to the host perovskite structure, it first must be modified with a few mol% lanthanide or rare earth cations to form oxygen vacancies [2–8]. The insertion of protonic species, i.e. protonation, is obtained under (high) water vapour pressure at medium temperature [6,9–14]. It was demonstrated that a few mol% of Ln-substitution gives rise to the crystal structure distortions, whereas the proton insertion re-symmetrises the structure [9,10]. The understanding of the complex behaviour of proton conducting perovskites is a key point to optimise their working time and proton conduction performance [11,12]. Despite the intensive studies, some important problems still re- main to be clarified: i) the real content of bulk protons (the only species responsible for proton conduction), usually not determined in previous studies on similar compounds [5–7,13–18]. It should be stressed that this problem is related to the systematic lack of differen- tiation between the bulk protons and the so-called surface protonic species, undesirable moieties adsorbed on the material surface [12]; ii) the location of protons in the host perovskite structure and their interactions with substituting elements; iii) the presence of structural phase modifications/transitions in the operating temperature/pres- sure range. Our previous (quasi-)elastic neutron scattering, TGA, Raman, IR and conductivity studies [8–12] allowed us to clarify some of these problems. First of all, we revealed that the protonation process is very complex and depends on many different parameters: sample densification/active surface area, and protonation conditions such as time, temperature, and pressure [8,12]. For instance, the low temperature/low water vapour pressure protonation and the use of poorly densified ceramics or powders can promote the adsorption of the surface protonic species (hydroxide, hydrocarbonates, etc.) and hinder the incorporation of bulk protons [12]. Note that the im- portant presence of the surface protonic species confuses the under- standing of fundamental aspects concerning the proton conductors such as the true nature of the conducting species [12]. Consequently, it is necessary to determine the real content of bulk protons in the sample. Due to the extremely high incoherent cross section value characteristic for hydrogen, we used the neutron scattering methods to determine the content of hydrogen-based species within the sam- ple. The comparison was made with TG analyses. These studies revealed that the content of bulk protons in the investigated Solid State Ionics 225 (2012) 214–218 ⁎ Corresponding author. E-mail address: slodczyk_aneta@yahoo.com (A. Slodczyk). 0167-2738/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2012.01.023 Contents lists available at SciVerse ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi