Solid oxygen nonstoichiometry

One of the prototypes of this behavior is the low-temperature form of tantalum pentoxide, L-Ta20s. The structure of this phase is ill defined, even though it is a stoichiometric oxide, and the room temperature stracture is a function of the prior thermal treatment temperature of the material. Reaction with other oxides, notably WO3, Zr02 and AI2O3, gives rise to solids with a broad oxygen nonstoichiometry. However, each composition appears to generate a uniquely ordered structure, which have been termed infinitely adaptive structures. 

Fig. 10.11. Data of oxygen nonstoichiometry of Lao.7 ro.23Cr03- Lao.sSro.iFeOs-a, Lao.9Sro.iCo03- and Lao,gSro.2Mn03.8 at 1000°C as a function of oxygen partial pressure. Solid lines are results from a fit of the random point defect model to the experimental data. Reproduced (slightly adapted) from...

Yang, Z. Lin, Y.S. A semi-empirical equation for oxygen nonstoichiometry of perovskite-type ceramics. Solid State Ionics 2002, 150, 245-254. 

Fig. 14. Dependence of the apical bond Cu2-01 on the oxygen nonstoichiometry. Note the abrupt change of the Zr-getteied samples (solid squares) at the T — O transition. NPD data, after Cava et al. (1990) and Hewat (1994) at r=5K, and Jorgensen et al. (1990a) (open circles) at RT.

Fig. 32. Lattice parameters of Er-123-06 j as a function of oxygen nonstoichiometry. Single-phase Rietveld refinements, solid signs two-phase refinements, open signs. The latter method shows a discontinuity of the c-axis. After Radaelli et al. (1992).

Mizusaki, J., Mori, N., Takai, H., Yonemura, Y., Minamiue, H., Tagawa, H., Dokiya, M., Inaba, H., Naraya, K., Sasamoto, T., and Hashimoto, T. (2000). Oxygen nonstoichiometry and defect equilibrium in the perovskite-type oxides Lai- Sr MnOs+j. Solid State Ionics 129 163-177. 

Onuma S, Yashtro K, Miyoshi S, Kaimai A, Matsumoto H, Nigara Y, Kawada T, Mizusaki J, Kawamura K, Sakai N, Yokokawa H (2004) Oxygen nonstoichiometry of perovskite-type oxide Lai.xCaxCr03.8(x = 0.1, 0.2, 0.3). Solid State Ion 174 287-293... 

Vashook W, Tolochko SP, Yushkevich II, Makhnach LV, Ktmonyuk IF, Altenburg H, Hauck J, Ullmann H (1998) Oxygen nonstoichiometry and electrical conductivity of the solid solutions La2 xSrxNiOy (0[Pg.1504]

Oishi M, Yashiro K, Sato K, Mizusaki J, Kawada T (2008) Oxygen nonstoichiometry and defect structure analysis of B-site mixed perovskite-type oxide (la, sr)(cr, M)03 a (M = ti, mn and fe). J Solid State Chem 181 3177-3184... 

Numerous efforts were xmdertaken to study the phase transformations and phase stability in LSM in a wide range of solid solutions. These materials exhibit a complicated dependence of the properties on the concentration of the Sr dopant and oxygen nonstoichiometry. Nowadays, it is well recognized that the dielectric, piezoelectric and other LSM properties are entirely related to the phase equilibrium and the phase separation that occurs under different thermodynamic conditions. 

Ullmaim, H., Paulsen, J., Trofimenko, N., and Teske, K. (1997) Oxygen nonstoichiometry and electrical conductivity of the binary strontium cobalt oxide SrCoO, . Solid State Ionics, 99, 23. 

S( )gaard, M., Hendriksen, P.V., and Morgensen, M. (2007) Oxygen nonstoichiometry and transport properties of strontium substituted lanthanium ferrite. J. Solid State Chem., 180,... 

Kharton, V., Patrakeev, M., Waerenborgh, J., et al. (2005). Methane oxidation over perovskite-related ferrites Effects of oxygen nonstoichiometry, Solid State Set, 7, pp. 1344-1352. 

Strobel P, Le Cras F, Seguin L, Arme M, Taraseon JM (1998) Oxygen nonstoichiometry in Li-Mn-O spinel oxides a powdta- neutron diffraetion study. J Solid State Chem 135 132-139... 

The microscopic mechanisms responsible for the electrochemical behavior of metallic and oxide electrodes were exhaustively analyzed in the literature [17-22, 24, 60, 62-69] and are outside of the main scope of this chapter. One should only mention that the solid-electrolyte additions into the electrode composition make it possible to increase reversibility and to enlarge the domain of temperatures and chemical potentials where the electrode can be safely used, a result of the TPB expansion and microstructural stabilization. Although the mixed-conducting and catalytically active additives such as doped ceria might also be useful from the cell impedance point of view, their use for the reference electrodes is limited if oxygen nonstoichiometry changes may occur under the cell operation conditions. 

Because of the charge equilibrium within the oxide, the electronic partial conductivity (electrons or holes) Oei and the ionic partial conductivity Oi are linked to the oxygen nonstoichiometry and, consequently, are two key parameters characterizing a MEEC. The methods developed for deconvoluting the ionic and electronic contributions to the total conductivity of a MIEC allow either the measurement of the partial conductivities, the diffusion coefficient of mobile defects or the transport numbers, either tei or hon- Only the methods involving a solid electrolyte cell are briefly described. Reviews papers can be referred [Heyne, 1982 Rickert, 1982 Riess, 1997 Weppner Huggins, 1978]. 

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