XPS and impedance spectroscopy of some oxygen vacancy conducting solid electrolyte ceramics A.F. Orliukas a, ⁎, T. Šalkus a , A. Kežionis a , V. Venckutė a , V. Kazlauskienė b , J. Miškinis b , G. Laukaitis c , J. Dudonis c a Faculty of Physics, Vilnius University, Saulėtekio al. 9/3, LT-10222 Vilnius, Lithuania b Institute of Applied Research, Vilnius University, Saulėtekio al. 9/3, LT-10222 Vilnius, Lithuania c Department of Physics, Kaunas University of Technology, Studentų str. 50, LT-51368 Kaunas, Lithuania abstract article info Article history: Received 18 June 2010 Received in revised form 13 October 2010 Accepted 1 November 2010 Available online 13 December 2010 Keywords: Ceramics Surfaces area S BET Impedance spectroscopy Conductivity XPS SEM The powder of 10GDC, 15SDC, and 8YSZ compounds with different surface areas (S BET ) was used for the sintering of the ceramics. The sintering of the ceramic samples was conducted in air at 1773 K. The surfaces of the ceramics were investigated by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The complex impedance and electric conductivity in frequency range (10–3⋅10 9 ) Hz and temperature range from 300 to 700 K were carried out. Relaxation dispersions of the electrical parameters were found for all compounds. The dispersions are caused by the oxygen vacancy (V O •• )transport in grain boundaries and bulk of the ceramic samples. The values of the bulk and total conductivities of the samples depend on the S BET of the powder used for sintering of the ceramics. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Solid electrolytes (SE) with fast oxygen vacancy (V O •• ) transport are attractive materials for applications in solid oxide fuel cells (SOFC) [1,2],O 2 and CO gas sensors [3,4]. Yttrium stabilized zirconia 8 mol% Y 2 O 3 stabilized ZrO 2 (8YSZ) is the most important SE in SOFCs operating in the high temperature regime. The values of ionic conductivity (σ) and its activation energy (ΔE σ ) are very important parameters of SE for application in SOFC. At 1073 K in the low frequency range (10–10 5 Hz) the value of total conductivity of YSZ was found to be σ t = 1.31 S⋅m -1 [5]. The bulk conductivity of polycrystal- line YSZ thin films deposited by the e-beam technique at temperature 660 K was found to be σ b = 4.12⋅10 -3 S⋅m -1 (its activation energy ΔE b = 0.95 eV) and depends on the technological conditions of the films' depositions [6,7]. One way of operating temperature lowering is to use a SE with higher V O •• conductivity, such as gadolinium doped ceria Gd 0.2 Ce 0.8 O 1.9 (20GDC), Gd 0.1 Ce 0.9 O 1.95 (10GDC), and Sm-doped ceria Sm 0.2 Ce 0.8 O 1.9 (20SDC), Sm 0.15 Ce 0.85 O 1.925 (15SDC). At 923 K the values of ionic conductivity of Ce 0.8 Gd 0.2 O 2-δ and Ce 0.8 Sm 0.2 O 2-δ were found to be 2.6 S⋅m -1 (ΔE σ = 0.95 eV) and 3.8 S⋅m -1 (ΔE σ = 0.75 eV) respectively [8]. At 973 K the value of the conductivity of commercial (CP) and synthesized (SP) polycrystalline Ce 0.8 Gd 0.2 O 1.9 samples was found to be 2.6 S⋅m -1 [9]. At 973 K the values of the bulk conductivity of Ce 0.85 Gd 0.15 O 1.925 and Ce 0.85 Sm 0.15 O 1.925 ceramics reach 20.9 S⋅m -1 (ΔE b = 0.7 eV) and 9.1 S⋅m -1 (ΔE b = 0.69 eV) respectively [10]. The above mentioned investigations of electric conductivity of SE were performed in the low frequency range (10 -3 –10 6 Hz) of the electric field. The electrical conductivity of Ce 0.9 Gd 0.1 O 1.95 in a reducing atmosphere has electronic and ionic components. The value of the electronic component is caused by a different valence ratio Ce 4+ /Ce 3+ in the GDC compounds [11]. The results of XPS investigation of SDC have shown that O 1s core level XP spectra consisted of double peaks. The two peaks represented O(1) in the lattice and an adsorption oxygen (O2). The binding energy of O(1) is lower than that of O(2) [12]. The authors [13] reported that in GDC thin films prepared by spray pyrolysis the O 1s core level XP spectra depend on the sput- tering time of GDC thin films. The O 1s core level XP spectra of YSZ is deconvoluted into two peaks where the main peak at binding energy 529.4 eV belongs to lattice oxygen and a smaller one at 531.8 eV can be ascribed to the adsorbed oxygen [14]. The high ionic conductivity of these SE and peculiarities of the ionic migration stimulate further investigations of the ionic transport properties in a wide frequency range. Investigation of the electric properties of materials with fast ion transport in a broad frequency range provides unique information on mass and charge transport, polarization phenomena, and relaxation processes in such systems. In this paper we report the results of the investigation of the com- plex electrical properties of Gd 0.1 Ce 0.9 O 1.95 (10GDC), Sm 0.15 Ce 0.85 O 1.925 (15SDC), and 8 mol% Y 2 O 3 stabilized ZrO 2 (8YSZ) ceramics sintered Solid State Ionics 188 (2011) 36–40 ⁎ Corresponding author. E-mail address: antanas.orliukas@ff.vu.lt (A.F. Orliukas). 0167-2738/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2010.11.001 Contents lists available at ScienceDirect Solid State Ionics journal homepage: www.elsevier.com/locate/ssi