La MnO

Fig. 61. Saturation magnetization and Curie temperature for the system La(Mni Ga )03. The points are Curie temperatures for La(Mno.75Coo.2 )03+a and La(Mno.fiCoo. 5)03+5. The double Curie temperature of the latter sample reflects two magnetic phases. (After Goodenough, Wold, Arnott, and Menyuk (225).)...

LaMn03 is an intrinsic p-type conductor. Electronic conductivity is enhanced by substitution of the La3+ site with divalent ions such as strontium or calcium. Of the alkaline-earth dopants, Sr substitution is preferred for SOLC applications because the resultant perovskite forms stable compounds with high conductivity in the oxidizing atmosphere found at the cathode [41], Extensive data show that La, xSi. MnO where x = 0.1 - 0.2, provides high conductivity while maintaining mechanical and chemical stability with YSZ [41, 42],... 

Currently, the standard SOFCs use yttria-stabilized zirconia (YSZ) (see Section 2.4.3) containing typically 8 mol% of Y02 as the electrolyte, a ceramic metal (a cermet) composed of Ni plus YSZ as the anode, and lanthanum strontium manganite (LSM) perovskite (La Sr, MnO,, ) as the cathode material [5,7,9,135],... 

Figure 20. Effect of internal pressure on the properties of (a) IVo-Coo... Sr.MnO and (b) Pro.7- La CaojMnOj. Note that substitution by a larger A-site cation renders the material FM (see insets). An insulator—metal transition is also observed (from Rao et al.33).

On the basis of the compositions obtained by neutron activation analysis two distinctive groups of pottery have been identified from the majolica sherds excavated from Spanish sites in the New World. The principal sites yielding majolica sherds analyzed in this project include Isabela, La Vega Vieja, Juandolio, and Convento de San Francisco in the Dominican Republic Nueva Cadiz in Venezuela and excavations in Mexico City at the Metropolitan Cathedral and for the Mexico City Metro transportation system. Concentrations of NazO, KzO, BaO, MnO, FezOs, RbzO, CszO, LazOs,... 

Fig. 9.8. Relative sensitivity coefficients in LA-ICP-MS [ La,0,/SrCO,/MnOi stoichiometric mixture perovskite (La , 5Sr ,MnO,)] compared to ICP-MS [A 0.7 ppm multi-element standard solution]. (Reproduced with permission of Springer-Verlag.)...

Horita, T., Yamaji, K., Ishikawa, M., Sakai, N., Yokokawa, H., Kawada, T., Kato, T. Active sites imaging for oxygen reduction at the La(l9Sr(l MnO i x/yttria-sta bi I ized zirconia interface by secondary-ion mass spectrometry. J. Electrochem. Soc. 1998,145, 3196-202. 

At the mixed conducting LSM cathode, the Oad can be ionized at the LSM surface besides the TPB, i.e., mixed-conducting path and TPB path in parallel. The contributions of the two pathways to the overall reaction might depend on the number of active sites on the LSM or on the microstructure. Mizusaki et al. " reported that die reaction involving Oad occurred dominantly around TPB in porous La(Ca)MnO, (LCM) cathode. This explanation seems to be valid. 

Monophasic Ln x MnOs (Ln = La, Nd) perovskites with high surface areas (8-27 m /g) were synthesised at mild conditions by the freeze-drying method, and were found to be active for the catalytic combustion of ethane at low temperatures (573 to 648 K). As a general troid, the substitution of the rare earth cation by potassium decreased the intrinsic activity, reduced the reaction order in oxygen and, for the more substituted samples (x>0.10), it increased the selectivity to ethene. It was found that the rare earth cation also influenced the catafytic activity of the substituted perovskites. These effects were analysed in terms of structural modifications induced by the introduction of potassium in the perovskites. 

The Mossbauer data presented in Table 7.9 are confirmative of the above assignments. For [la]+, [la], and [la]-, isomer shifts are all observed in the narrow range of 0.08-0.01 mm/s and quadrupole splittings at 1.4—2.0 mm/s, a clear indication that the MNO 6 moieties are retained irrespective of the charge of the complexes or dithiolene oxidation level. In contrast, the [la]2- complex shows an increase and decrease of the above parameters, respectively, suggesting an MNO 7 moiety, in agreement with previous reports (cf. Table 7.3). 

By performing the CV experiments, only three reversible waves are found, with half-wave potentials as detailed in Table 7.9. The fourth expected reduction eventually leading to [la]3- has not been observed, although it has been recorded for a related complex with the maleonitrile-l,2-dithiolate ligand, at —1.83 V. The [la]3-complex should contain the MNO 8 moiety. As discussed in Section 7.5, iron complexes of this configuration are scarce, and very elusive to a proper characterization. 

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