Studies of defect structure and oxidation-reduction behavior of undoped LaMnO/sub 2/, Sr-doped LaMnO/sub 3/, and Mg-doped LaMnO/sub 3/
Undoped LaMnO/sub 3/, Sr-doped LaMnO/sub 3/ and Mg-doped LaMnO/sub 3/ 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. Results showed that both Sr and Mg doping caused the LaMnO/sub 3/ to dissociate at higher oxygen activities than for undoped LaMnO/sub 3/. 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.
- Research Organization:
- Missouri Univ., Rolla (USA)
- OSTI ID:
- 7203157
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
360202* -- Ceramics
Cermets
& Refractories-- Structure & Phase Studies
360204 -- Ceramics
Cermets
& Refractories-- Physical Properties
ALLOYS
CHALCOGENIDES
CHEMICAL REACTIONS
CRYSTAL DEFECTS
CRYSTAL STRUCTURE
DOPED MATERIALS
LANTHANUM COMPOUNDS
LANTHANUM OXIDES
MAGNESIUM ADDITIONS
MAGNESIUM ALLOYS
MANGANESE COMPOUNDS
MANGANESE OXIDES
MATERIALS
METALLURGICAL EFFECTS
OXIDES
OXYGEN COMPOUNDS
PEROVSKITES
PHASE STUDIES
PHYSICAL PROPERTIES
RARE EARTH COMPOUNDS
REDOX REACTIONS
SEEBECK EFFECT
STRONTIUM ADDITIONS
STRONTIUM ALLOYS
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPOUNDS