"Undoped LaMnO₃, Sr-doped LaMnO₃ and Mg-doped LaMnO₃ showed reversible oxidation-reduction behavior. These perovskites can be excess, stoichiometric or deficient in oxygen content depending on the specific conditions. Under very reducing conditions these oxides will decompose into new phases. Phase stabilities for these oxides were determined. The results showed that both Sr and Mg doping caused the LaMnO₃ to dissociate at higher oxygen activities than for undoped LaMnO₃.
Defect models were proposed to interpret the TG results, in which metal vacancies are assumed for the oxygen excess condition and oxygen vacancies are assumed for the oxygen deficient condition. Thermodynamic properties were calculated which supported the model. Results for both dc and ac electrical conductivities showed p-type behavior. The Sr dopant enhanced the conductivity while Mg dopant lowered the conductivity.
The measured Seebeck coefficients confirmed that the conduction was due to holes. The small polaron hopping model was used to interpret the electrical and Seebeck data. Calculations of the carrier concentrations, activation energies and mobilities were also performed. The results suggested that the electrical conductivity for these perovskites was dominated by the mobility rather than by the carrier concentration"--Abstract, page ii.
Anderson, H. U. (Harlan U.)
Moore, Robert E., 1930-2003
Ownby, P. D.
Sparlin, Don M.
Materials Science and Engineering
Ph. D. in Ceramic Engineering
University of Missouri--Rolla
xi, 139 pages
© 1987 Jen-Ho Kuo, All rights reserved.
Dissertation - Restricted Access
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Kuo, Jen-Ho, "Studies of defect structure and oxidation-reduction behavior of undoped LaMnO₃, Sr-doped LaMnO₃ and Mg-doped LaMnO₃" (1987). Doctoral Dissertations. 640.