\"Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the system Y1-xCaxMnO3 were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Thermal expansion was also measured. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ x ≤ 0.80. Seebeck coefficient data did not support the traditional assumption that Mn is present in Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which included the thermally excited disproportionation of Mn3+ into Mn2+ and Mn4+ pairs. The Seebeck data could be explained with this model by assuming that divalent Mn cations were site blockers in the conduction process. Since compositions in Y1-xCaxMnO3 exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced, several compositions in the system La1-xCaxMnO3 were studied in order that the defect model could be applied to the oxygen activity-dependent region in manganites. The disproportionation model was successful in explaining the experimentally observed dependence of oxygen stoichiometry, electrical conductivity, and Seebeck coefficient upon ambient oxygen activity\"--Abstract, page iii.
","abstract_html":"<p>"Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the system Y<sub>1-x</sub>Ca<sub>x</sub>MnO<sub>3</sub> were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Thermal expansion was also measured. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ x ≤ 0.80. Seebeck coefficient data did not support the traditional assumption that Mn is present in Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which included the thermally excited disproportionation of Mn<sup>3+</sup> into Mn<sup>2+</sup> and Mn<sup>4+</sup> pairs. The Seebeck data could be explained with this model by assuming that divalent Mn cations were site blockers in the conduction process. Since compositions in Y<sub>1-x</sub>Ca<sub>x</sub>MnO<sub>3</sub> exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced, several compositions in the system La<sub>1-x</sub>Ca<sub>x</sub>MnO<sub>3</sub> were studied in order that the defect model could be applied to the oxygen activity-dependent region in manganites. The disproportionation model was successful in explaining the experimentally observed dependence of oxygen stoichiometry, electrical conductivity, and Seebeck coefficient upon ambient oxygen activity"--Abstract, page iii.</p>","abstract_has_math":false,"creators":["Stevenson, Jeffry W."],"institution":"University of Missouri--Rolla","degree_name":"Ph. D. in Ceramic Engineering","degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":[],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2016,"date_issued":"2016-02-10T08:00:00Z","date_published":"2016-02-10T08:00:00Z","updated_at":"2026-07-24T03:19:21Z","subjects":["Ceramic Materials"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://scholarsmine.mst.edu/doctoral_dissertations/484","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:creator","label":"Author","values":["Stevenson, Jeffry W."]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2016-02-10T08:00:00Z"]},{"key":"dc:type","label":"Dc Type","values":["Dissertation - Restricted Access"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph. D. in Ceramic Engineering"]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Missouri--Rolla"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Ceramic Materials"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://scholarsmine.mst.edu/doctoral_dissertations/484"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["\"Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the system Y1-xCaxMnO3 were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Thermal expansion was also measured. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ x ≤ 0.80. Seebeck coefficient data did not support the traditional assumption that Mn is present in Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which included the thermally excited disproportionation of Mn3+ into Mn2+ and Mn4+ pairs. The Seebeck data could be explained with this model by assuming that divalent Mn cations were site blockers in the conduction process. Since compositions in Y1-xCaxMnO3 exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced, several compositions in the system La1-xCaxMnO3 were studied in order that the defect model could be applied to the oxygen activity-dependent region in manganites. The disproportionation model was successful in explaining the experimentally observed dependence of oxygen stoichiometry, electrical conductivity, and Seebeck coefficient upon ambient oxygen activity\"--Abstract, page iii.
"]},{"key":"dc:title","label":"Title","values":["Electrical and structural properties of compositions in the systems Y₁₋ₓCaₓMnO₃ and La₁₋ₓCaₓMnO₃"]}]}],"canonical_facts":{"dc:creator":["Stevenson, Jeffry W."],"dc:date.available":["2016-02-10T08:00:00Z"],"dc:description.abstract":["\"Electrical conductivity, Seebeck coefficient, and thermogravimetric behavior of compositions in the system Y1-xCaxMnO3 were studied as functions of temperature and ambient oxygen activity in order to determine the mechanism of electrical transport and defect structure. Thermal expansion was also measured. Electrical conduction appeared to occur via a small polaron hopping mechanism for compositions with 0.30 ≤ x ≤ 0.80. Seebeck coefficient data did not support the traditional assumption that Mn is present in Mn perovskites only in the +3 and +4 valence states. A new defect model was developed which included the thermally excited disproportionation of Mn3+ into Mn2+ and Mn4+ pairs. The Seebeck data could be explained with this model by assuming that divalent Mn cations were site blockers in the conduction process. Since compositions in Y1-xCaxMnO3 exhibited very slight oxygen activity-dependent behavior as the ambient oxygen activity was reduced, several compositions in the system La1-xCaxMnO3 were studied in order that the defect model could be applied to the oxygen activity-dependent region in manganites. The disproportionation model was successful in explaining the experimentally observed dependence of oxygen stoichiometry, electrical conductivity, and Seebeck coefficient upon ambient oxygen activity\"--Abstract, page iii.
"],"dc:identifier":["https://scholarsmine.mst.edu/doctoral_dissertations/484"],"dc:subject":["Ceramic Materials"],"dc:title":["Electrical and structural properties of compositions in the systems Y₁₋ₓCaₓMnO₃ and La₁₋ₓCaₓMnO₃"],"dc:type":["Dissertation - Restricted Access"],"thesis:degree_name":["Ph. D. in Ceramic Engineering"],"thesis:institution_name":["University of Missouri--Rolla"]},"updated_at":"2026-07-24T03:19:21Z"}