The Effects of Ca and Mn Excess Co-Doping in CMR Manganites Solid Solution Structures

Figueiras, Fábio; Vieira, Joaquim M.; Guzik, M.E.; Legendziewicz, J.; Tavares, Pedro B.; Amaral, Vitor S.

doi:10.4028/www.scientific.net/MSF.514-516.294

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Home Materials Science Forum Advanced Materials Forum IIIThe Effects of Ca and Mn Excess Co-Doping in CMR...

The Effects of Ca and Mn Excess Co-Doping in CMR Manganites Solid Solution Structures

Abstract:

A comprehensive study of CMR manganite related phases, particularly those that develop under the effects of Ca and Mn-excess co-doping is undertaken. The relationships between phase composition, processing and observed crystalline structure are investigated for co-precipitated powders of composition La1-xCaxMn1+zO3+δ, thermally treated at 800 and 1000 °C in air for Ca contents of x=0.10 and x=0.15 and Mn content from z=0 up to z=0.88. A relevant structural transition from orthorhombic to rhombohedric symmetry is observed as a function of Mn excess near 25% A site vacancies. This solid solution is in equilibrium with the conjugated phases, either LaMn7O12 at 800°C, or Mn3O4 at 1000°C, respectively. Results suggest that at the polymorphic phase transition the solid solution is stable enough to slow down Mn diffusion into the perovskite cell. Ca-doping introduces stability in the perovskite structure and broadens the domain for phase formation reaction. The solid solution limit of the Ca-manganite solid solution is set above 50% Mn excess.

Info:

Periodical:

Materials Science Forum (Volumes 514-516)

Main Theme:

Advanced Materials Forum III

Edited by:

Paula Maria Vilarinho

Pages:

294-298

DOI:

https://doi.org/10.4028/www.scientific.net/MSF.514-516.294

Citation:

F. Figueiras et al., "The Effects of Ca and Mn Excess Co-Doping in CMR Manganites Solid Solution Structures", Materials Science Forum, Vols. 514-516, pp. 294-298, 2006

Online since:

May 2006

Authors:

Fábio Figueiras, Joaquim M. Vieira, M.E. Guzik, J. Legendziewicz, Pedro B. Tavares, Vitor S. Amaral

Keywords:

Crystal Structure, Manganite, Solid Solution, Vacancy

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References

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Paper TitlePages

Mechanism of a Solid-State Formation of La_1-xSr_xMnO_3+δ (0 < x < 0.5) and Magnetic Characterization thereof

Authors: V. Uskoković, Miha Drofenik

Abstract: Investigations of the influence of synthesis procedures and LaSr-manganite stoichiometries on the Curie point and other magnetic characteristics of the material, being the topic of this work, are attractive since they present a necessary primal step in the intended development of nano-magnetic drug carriers based on these materials. In the course of such an investigation, differences in the mechanisms of the formation of desired manganite compounds by following a classical solid-state preparation method, depending on various stoichiometries used, were noticed, with the reaction pathways thereof outlined onward.

119

Influence of the Transition to Nanoscaled State on Electrochemical Properties of LaMnO_3+δ Oxide

Authors: G.A. Kozhina, A.N. Ermakov, V.B. Fetisov, A.V. Fetisov, Anatoly Yakovlevich Fishman, S.A. Petrova, Robert Grigorievich Zakharov, K. Y. Shunyaev, S.V. Rassokhin

Abstract: The electrochemical behavior of perovskite type LaMnO3 (LMO) oxides with different mean particle size was studied by voltammetry with the use of a carbon paste electroactive electrode. Three stages of electrochemical reduction were recognized. The first two of them are related to the release of oxygen from the crystal lattice in the range of two side nonstoichiometry of LaMnO3±δ whereas the final stage is conditioned by the decomposition of LaMnO3-δ into new phases. The nature of these phases and their formation mechanisms are different for nano- and microparticles. The utmost size effect appears on cathodic curves recorded from the stationary potential. The effect is not only due to the size factor but also due to the difference in electrochemical properties of nano- and microparticles. While the decomposition of LaMnO3 microparticles proceeds into La2O3 and MnO oxides, the nanoparticles decompose through the intermediate stage of Mn3O4 formation in accordance with the transformation sequence principle.

354

Microstructure and Phase Analysis of La_0.8Ba_0.2Ti_xMn_(1-x)O₃ System for Microwave Absorber Material (x = 0 – 0.7)

Authors: Wisnu Ari Adi, A. Manaf

Abstract: The synthesis and characterization of the magnetic materials of La0.8Ba0.2Mn (1-x)TixO3 system (x = 0 0.7) by mechanical alloying process have been performed. This magnetic material is prepared by oxides, namely La2O3, BaCO3, MnCO3 and TiO2. The mixture was milled for 10 h and then sintered at 1000 ° C for 10 h. The refinement results of x-ray diffraction pattern showed that the doping concentration (x < 0.5) was a single phase, which has a structure monoclinic (I12/a1) with lattice parameters a = 5.5169(5) Å, b = 5.5437(5) Å and c = 7.8553(7) Å, = 90o and 89.75(1) o, V = 240.25(4) Å3 and 6.345 gr.cm-3. The microstructure analysis showed that the particle shapes was polygonal with the varied particle sizes distributed homogeneously on the surface of the samples. We concluded that the maximum number of titanium atoms substituting manganese atom is around x ~ 0.43 without changing the structure of this system.