Perovskite-type oxides pressure

Perovskite-type oxides with Fe , for example, SrFe03, can be made under high 02 pressures and spinels such as Ba2Fe04 can be made by the reaction... 

The limits of integration are the oxygen partial pressures maintained at the gas phase boundaries. Equation (10.10) has general validity for mixed conductors. To carry the derivation further, one needs to consider the defect chemistry of a specific material system. When electronic conductivity prevails, Eqs. (10.9) and (10.10) can be recast through the use of the Nemst-Einstein equation in a form that includes the oxygen self-diffusion coefficient Dg, which is accessible from ionic conductivity measurements. This is further exemplified for perovskite-type oxides in Section 10.6.4, assuming a vacancy diffusion mechcinism to hold in these materials. 

FIGURE 9.3 Diagram for the variation of the oxygen/metal stoichiometry with the partial pressure of oxygen for different perovskite-type oxides. (From figure 1 of Girdauskaite et al., 2007. J. Solid State Electrochem. 11, 469-477, with permission.)... 

For a doped oxide M2O3 exhibiting anti-Frenkel disorder, Colomban and Novak present a sehematie Kroger-Vink diagram of the extrinsic and intrinsic point defects as a function of the partial water pressure. With regard to electrical properties, the proton conductivity in the binary metal oxides is usually much lower than in the perovskite-type oxides. ... 

An important study of charge carrier in a typical ferroelectric perovskite-type oxide BaTiOa was published in 1964 by Glower and Heckman [10]. The title of the paper Conduction - Ionic or Electronic in BaTiOa was attractive for materials researchers in those days. In their paper, they reported about conduction species in barium titanate as follows Usual practice of authors has been to make the tacit assumption that conduction is exclusively electronic. There is no priori assurance that this is true. Also, they wrote In fact, to our knowledge, no one has to date addressed himself to the primary problem of transport, i.e., does conduction occur via the motion of electrons or of ions The purpose of their study was to answer this essential question from experimental results. They applied Cell [1] to BaTiOa specimens for different oxygen partial pressures Pi and P2-... 

A characteristic feature of perovskite-type oxide ion conductors is that they are often accompanied with p-type electronic conduction under an oxidizing atmosphere such as air at elevated temperatures. As described in Section 3.2, the contribution of electronic conduction depends on P02 in the atmosphere and temperature. As a typical example, Fig. 3.4 shows the P02 dependence of conductivities of CaTiOs- and SrTiOs-based solid solutions at 800°C [16]. P-type electronic conduction appears in the region of high P02 and n-type one under low oxygen partial pressure, i.e., a reducing atmosphere. The shape of the curve Incr lnPo2 is essentially the same as that shown schematically in Fig. 3.1. In many fluorite-type oxide ion conductors such as stabilized zirconias and... 

In order to examine the mechanism of the oxygen reduction in Lai xSrx. Coi yFey03 5 (LSCF) in this paper, complex studies over the stracture of the ionic and electronic defects, resulting from the deviation from stoichiometry or doping with different ions, were carried as a function of temperature and oxygen partial pressure. The results allowed for designing functional properties of perovskite-type oxides, perspective cathode materials for electrochemically effective IT-SOFC. 

Henderson, N.L., Back, J., Halasyamani, P.S., and Schaak, R.E. (2007) Ambient-pressure synthesis of SHG-active EujTijOy with a [110] layered perovskite structure suppressing pyrochlore formation by oxidation of perovskite-type... 

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