Strontium-substituted lanthanum

Baythoun, M. S. G Sale, F. R. 1982. Production of strontium-substituted lanthanum manganite perovskite powder by the amorphous citrate process. /. Mat. Sci. 17 2757-2769. 

Paulik SW, Baskaran S, and Armstrong TR. Mechanical properties of calcium- and strontium-substituted lanthanum chromite. J. Mater. Sci. 1997 33 2397-2404. 

Y. Denos, F. Morin and G. Trudel, Oxygen diffusivity in strontium substituted lanthanum cobaltite, in T.A. Ramanarayanan, W.L. Worrel and H.L. Tuller (Eds.), Proceedings of the 2nd International Symposium on Ionic and Mixed Conducting Oxide Ceramics. The Electrochemical Society, Pennington, NJ, 1994, pp. 150-158. 

Faaland S, Einarsmd MA, Grande T. Reactions between calcium and strontium substituted lanthanum cobaltite ceramic membranes and calcium silicate sealing materials. Chem Mater. 2001 13 723. 

Wiik, K., Schmidt, C. R., Faaland, S., Shamsili, S., Einarsrud, M.-A., and Grande, T. (1999). Reactions between strontium-substituted lanthanum manganite and yttria-stabilized zirconia I. Powder samples./. Am. Ceram. Soc. 82 721-728. 

Deng, J., Zhang, L., Daia, H., et al. (2009). Hydrothermally Fabricated Single-crystalline Strontium-substituted Lanthanum Manganite Microcubes for the Catalytic Combustion Of Toluene, J. Mol. Catal. A Chem., 299, pp. 60-67. 

Baythoun M.S.G., Sale F.R. Production of strontium-substituted lanthanum manganite perovskite powder by the amorphous citrate process. J. Mater. Sci. 1982 17 2757-2769 Bernard M.I.B., Soledade L.E., Santos I.A., Leite E.R., Longo E., Varela J.A. Influence of the concentration of 86203 and the viscosity of the precursor solution on the electrical and optical properties of Sn02 thin films produced by the Pechini method. Thin Solid Films 2002 405 228-233... 

For strontium-doped lanthanum chromites, the precipitation of SrO is not possible, because strontium ions are more stable in the perovskite stmctuie than the lanthanum ions. Lanthanum oxide, La203, is often precipitated instead of SrO. This causes the disintegration of sintered specimens at ambient temperatures by the volume change associated with the formation of lanthanum hydroxide, La(OH)3, due to the reaction of La203 with the water vapor in the air (Meadowcroft, 1969 Sakai et al., 1990a). The substitution of transition metals such as zinc (Hayashi et al., 1988), cobalt (Zhou et al., 1996), or vanadium (Larsen et al., 1997) have been used to improve the sintering of strontium substituted lanthanum chromite. The substitution of strontium and transition metals is often utilized for intercoimects of the planar type... 

The superconducting oxides include both perovskites and Ruddlesden-Popper compounds which have an orthorhombic arrangement of cubic cells, alternatively of the perovskite and sodium chloride structures. The common feature of all of these is the presence of copper as a major component. The first ceramic superconductor was a lanthanum-strontium substituted cuprate (Lai Sr Cu04 z), which is a perovskite, but subsequently the inter-oxide compound Y203 2BaO 3CuO, commonly referred to as a 123 compound, was shown to have superior performance. The speculation concerning the conduction mechanism is that this involves either Cu3+-Cu2+ positive hole... 

LaCrC>3 is one of the family of lanthanide perovskites RTO3, where R is a lanthanide and T is a period 4 transition element. In the cubic unit cell R occupies the cube corners, T the cube centre and O the face-centre positions. The coordination numbers of T and R are 6 and 8 respectively. LaCrC>3 loses chromium at high temperatures, leaving an excess of O2- ions. The excess charge is neutralized by the formation of Cr4+ which results in p-type semiconductivity with hole hopping via the localized 3d states of the Cr3+ and Cr4+ ions. The concentration of Cr4+ can be enhanced by the substitution of strontium for lanthanum. A 1 mol.% addition of SrO causes the conductivity to increase by a factor of approximately 10 (see Section 2.6.2). 

Wandekar, R.V. Wani, B.N. Bharadwaj, S.R. (2009). Crystal Structure, Electrical Conductivity, Thermal Expansion and Compatibility Studies of Co-substituted Lanthanum Strontium Manganite System Solid State Science, Vol. 11, No. 1, 0anuary 2009), pp. 240-250, ISSN 1293-2558... 

Marinho EP, Souza AG, de Melo DS, Santos IMG, Melo DMA, and da Silva WJ. Lanthanum chromites partially substituted by calcium strontium and barium synthesized by urea combustion—Thermogravimetric study. J. Thermal Analysis Calorimetry 2007 87 801-804. 

Fig. 1 Two parent compounds of the family of ceramic oxides that under hole doping develop HTS. (a) In LaCuO, Lanthanum is substituted by Strontium or Barium. Ion valences, AF order, and the JT unit formed by the CuOg octahedral are shown, (b) YBaCuOy-g reaches HTS if oxygen is introduced into the Cu-0 chains. The three lattice constants for the unit cell along the three axes are a = 3.81 A, b = 3.88 A and c = 11.64 A. Average Cu-O distances are indicated as well...

A series of lanthanum, partially substituted by strontium or cerium, manganese perovskites are synthetized. Some of them are also substituted by noble metals (Pt and/or Pd) or by copper in B-site. To improve homogeneity and to lower the phase formation temperature, a sol-gel process is used for the synthesis. 

Lanthanum substitution by strontium has been widely used to improve catalytic performance [5-7] arguing the increase in Mn + content for charge compensation. In fact, the determination by titration of Mn + content shows, on the opposite, a decrease in Mn4+ content accompanied by a decrease in oxygen stoichiometry. This is in accordance with the results of Kuo et al. [8] who determined oxygen stoichoimetry by TGA measurements as well as other works based on Mn + titration [9, 10]. 

The substitution of the alkaline earth for lanthanum in different amounts has great impact on the electron-conducting properties. This is principally because strontium (and calcium or barium) has a valence of 2+ whereas lanthanum exists in the 3-i- form. Thus, as strontium is substituted for lanthanum, there arises a need to equilibrate the charge of the cations and oxygen anions in the perovskite. 

The elements yttrium and lanthanum are interchangeable in terms of chemical properties (they are in the same group in the periodic table) although they differ in size. The same is true of strontium and barium in Group II of the periodic table. The idea behind the substitution of the large element for a smaller element was based on observations that Tc could be raised under an applied pressure. Substitution of a larger element for a smaller one was thought to produce an internalized pressure effect. Table 30.12 lists some of these compounds and their T. ... 

Frozandeh-Mehr, E., Malekzadeh, A., Ghiasi, M., Gholizadeh, A.. Mortazavi, Y., and Khodadadi, A. (2012) Effect of partial substitution of lanthanum by strontium or bismuth on structural features of the lanthanum manganite nanoparticles as a catalyst for carbon monoxide oxidation. Catal Commun., 28, il- Sl. 

Therefore, many researches were performed to examine the influence of lanthanum substitution in the A site of the perovskite by difierent cations. Rynkow-ski et al. [29] showed that a small amount of strontium in the perovskite-Uke K2Nip4 oxide La2- Sr,cNi04 slightly decreases the catalytic activity but improves the stability of the catalyst. XRD analysis revealed the presence of SrCOs for X = 0.25 and 0.5 proving that the accommodation of strontium in the structure of the lanthanum nickel oxide is not complete, even after a calcination step at... 

LSM (Lanthanum Strontium Manganite). For the electrodes, Lai Sr Mn03 is a good electronic conductor. To compensate the decrease of positive charge due to the substitution of La " " cations by Sr + cations, some manganese cations change their degree of oxidation from +3 to +4. The electrons can hop between the Mn + and Mn " ". The... 

Zhang, H.M., Yamazoe, N., and Teraoka, Y. Effects of B site partial substitutions of perovskite-type lanthanum strontium cobalt oxide (Lao.6Sro.4Co03) on oxygen desorption. J. Mater. Sci. Lett. 1989,8, 995-996. 

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