Praseodymium Doped Ceria Oxygen Surface Exchange Coefficient and Film Stress Measurements Via the Curvature Relaxation Technique
2016; Institute of Physics; Volume: MA2016-02; Issue: 53 Linguagem: Inglês
10.1149/ma2016-02/53/4103
ISSN2152-8365
Autores Tópico(s)Diamond and Carbon-based Materials Research
ResumoIntroduction Praseodymium doped ceria (PCO) is a mixed ionic electronic conductor (MIEC) that can be used as a cathode material in solid oxide fuel cells (SOFCs). Under SOFC operating conditions, PCO undergoes the following reaction [1]: ½ O 2 + 2Pr ’ Ce + V Ӧ à 2Pr Ce + O o x The kinetics of this oxygen exchange reaction are represented by the oxygen surface exchange coefficient ( k chem ). In this work, simultaneous k chem and stress measurements on PCO thin films atop yttria-stabilized zirconia (YSZ) substrates were performed from 625-725 o C using the curvature relaxation (κR) technique. Experimental Methods Phase pure Pr 0.1 Ce 0.9 O 1.95 powder was prepared through glycine nitrate combustion and subsequent powder calcination in air. (001) oriented 9.5% YSZ substrates (Crystec, GmbH) were pre-annealed at 1450 o C for 20 hours. PCO thin films were sputtered onto YSZ substrates at room temperature and then sintered for 1 hour at 1100 o C. The bilayer structures were tested using a multi beam optical stress sensor (MOSS) from 625 o C to 725 o C with 25 o C increments. The κR technique determines k chem by fitting a solution of Fick’s 2 nd Law to the curvature response of mechano-chemically active film | inert substrate bilayers reacting to sudden changes in oxygen partial pressure (synthetic air (21% O 2 - 79% Ar) and 10% synthetic air - 90% Ar) [2,3]. Film stress values were calculated using Stoney’s equation [2,3]. In order to compare the k chem values with those in the literature, electrically-measured PCO k q values from the literature [4] were turned into k chem values by multiplying them by the corresponding PCO thermodynamic factor from Ref [5]. Results Figure 1 shows how the k chem value measured via the κR technique compares with literature [4,5] values. Conclusions The PCO k chem and activation energies measured here are significantly different than those reported in the literature. Although additional work is needed before these effects can be explained in full, these discrepancies may be caused by the different synthesis techniques (sputtering vs. pulsed laser deposition) used to produce the two films shown in Figure 1. Acknowledgements This material is based upon work supported by the Department of Energy under Award Number DE-FE0023315. References [1] Bishop S R, Stefanik T S, Tuller H L. Journal of Materials Research, 2012, 27(15): 2009-2016. [2] Yang Q, Burye T E, Lunt R R, et al. Solid State Ionics, 2013, 249: 123-128 [3] Yang Q, Nicholas J D. Journal of the Electrochemical Society, 2014, 161(11): F3025-F3031. [4] Chen D, Bishop S R, Tuller H L. Journal of Electroceramics, 2012, 28(1): 62-69. [5] Chen D, Bishop S R, Tuller H L. Advanced Functional Materials, 2013, 23(17): 2168-2174. Figures Figure 1. A comparison of literature and κR-measured PCO k chem values [4,5]. Figure 1
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