Oxygen non-stoichiometry

Here the site fractions of the defects in eq. (9.102) are expressed in terms of the oxygen non-stoichiometry parameter 8. 

Patcas, F Buciuman, FC Zsako, J. Oxygen non-stoichiometry and reducibility of B-site substituted lanthanum manganites, Thermochimica Acta, 2000, Volume 360, Issue 1,71-76. 

Magnetic materials can be classified into two groups metal and alloy materials, and metal oxide materials represented by ferrites. We here describe the Mn-Zn ferrites, which are used, for example, as the magnetic heads in magnetic recording, focusing on the preparative processes and physical properties, which are closely related to the oxygen non-stoichiometry. 

Fig. 3.8 Relation between temperature, oxygen partial pressure, and oxygen non-stoichiometry, y, for the starting composition (ZnO)]8.3(MnO)26.8(Fe203)54.9. y denotes the weight gain from the standard composition.

T. Tanaka, Study on high-dense Mn-Zn Ferrite prepared by controlling the oxygen non-stoichiometry. Thesis, Keio University, 1981. 

The incorporation of Sr thus leads to cheirge compensation by the formation of Fe ions, which is in accord with the Verwey principle of controlled ionic valency [162]. The extent of oxygen non-stoichiometry is established by the following defect chemical reactions. 

A proper description of electronic defects in terms of simple point defect chemistry is even more complicated as the d electrons of the transition metals and their compounds are intermediate between localized and delocalized behaviour. Recent analysis of the redox thermodynamics of Lao.8Sro,2Co03. based upon data from coulometric titration measurements supports itinerant behaviour of the electronic charge carriers in this compound [172]. The analysis was based on the partial molar enthalpy and entropy of the oxygen incorporation reaction, which can be evaluated from changes in emf with temperature at different oxygen (non-)stoichiometries. The experimental value of the partial molar entropy (free formation entropy) of oxygen incorporation, Asq, could be... 

Girdauskaite, E., llllmann, H., Al Daroukh, M., Vashook, V., Billow, M., and Guth, U. 2006. Oxygen non-stoichiometry and electrical conductivity of Pr2 iSrjNiO4 with x = 0-0.5. Solid State Ionics 167, 1163-1171. 

In the case of lead ruthenate, the oxygen non-stoichiometry concept can be developed further by combining it with the known reactions of the variable valence ruthenium. It has been shown in this work that these same catalysts can cleave carbon-carbon double bonds (3) in a manner analogous to that of osmium and ruthenium tetroxiHe (1,1). It is known (12) that OSO4 (and presumably RUO4) cleave olefins via complexes with the structure ... 

The studied catalysts have the following general fonnula Lao.2Sro.8Miil-x-yB xy03-A, where B is a noble metal (Pt, Pd and Ru), F cation vacancies and 1 refers to the oxygen non stoichiometry. The perovskite phases are obtained by decomposition of equimolar mixtures of the corresponding metal nitrates (La, Sr and Mn) and noble metal (Pt, Pd and Ru) chlorides. 

McIntosh S, Vente JF, Haije WG, Blank DHA, Bouwmeester HJM. Phase stability and oxygen non-stoichiometry of SrCo0.8Fe0.203-d measured by in-situ neutron difiiaction. Solid State Ionics. 2006 177 833. 

More recently efforts have been directed towards the development of perovskite related cathode materials, particularly those of the K2Nip4 structure type [2,3], Fig. 1. These oxides consist of alternating layers of ABO3 and AO (rock salt) and have been demonstrated to accommodate a significant oxygen non-stoichiometry. 

The oxygen non-stoichiometry in the "123" oxide YBa2Cu307. is one of the most complex phenomena which has been observed in these cuprates. Its study is of capital importance since it influences drastically the critical temperature of this phase which... 

All these results show that the oxygen non stoichiometry is the key to the optimization of the superconducting properties and especially determines the critical temperature of the thallium cuprates, owing to its great influence upon the hole carrier density of these compounds. 

Since 1970, the perovskite type oxides, typically rare earth oxides with a (ABO3) formula, have been suggested as substitutes for noble metals in automotive exhaust catalysis (1). The most studied perovskites are LaM03 ( M = first row transition metal ) (2,3,4), where M is considered as the active site of the catalyst. The cobaltites show good activity as oxidation catalysts, the reactivity seems to depend on the facility of cobalt to undergo the transition Co Co m, which may be correlated to an oxygen non stoichiometry, and to the spin state of the cation (5). Furthermore, series of LaM03 oxides revealed similar profiles for CO adsorption studies as for NO adsorption, with NO adsorption maxima for M = Mn and Co (6). The reactivity of these catalysts has been shown not only to depend on the surface area, but also on the preparation process (7). 

More recently, the maximum oxygen non-stoichiometry in SMMO was successfully increased through partial substitution of Mo(Vl) by Nb(V), without compromising the stability of the double perovskite [85]. The increase in oxygen non-stoichiometry suggests that more Mo /Mo " redox centers are created, which are expected to increase both oxygen ion conductivity and fuel oxidation rates. 

Patrakeev, M.V., Leonidov, lA., and Kozhevnikov, VX. (2010) Applications of Coulometric titration for studies of oxygen non-stoichiometry in oxides. /. Solid State Electrochem., 15 (5), 931 954. 

Chen, W., Nijmeijer, A., and Winnubst, L (2012) Oxygen non-stoichiometry determination of perovskite materials by a carbonation process. Solid State Ionics, 229, 54-58. 

Jin YC, Lin CY, Duh JG (2012) Improving rate capability of high potential LiNio.5Mni 504-4 cathode materials via increasing oxygen non-stoichiometries. Electrochim Acta 69 45-50... 

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