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Title: Enhancement of redox- and phase-stability of thermoelectric CaMnO{sub 3−δ} by substitution

Redox Reactivity and structural phase transitions have a major impact on transport and me-chemical properties of thermoelectric CaMnO{sub 3−δ}. In this study series of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} (0≤x,y≤0.8) compounds, each with A-site (Dy{sup 3+}, Yb{sup 3+}) or B-site (Nb{sup 5+}, Ta{sup 5+} and Mo{sup 6+}, W{sup 6+}) substitution, were synthesized and crystallographically analyzed. It was found that the high-temperature oxygen content is widely independent from the substituent. Subsequently, with increasing temperature the differences in the Seebeck coefficient vanish above 1200 K. With increasing substitution the orthorhombic distortion of the perovskite-like phase increases. The orthorhombic distortion and the upper temperature limit of the stability of the orthorhombic crystal structure show an almost linear dependency. Accordingly, the mechanical stability of all-oxides thermoelectric converters at temperatures exceeding 1000 K will be increased employing materials with high substitution level and substituents inducing a high orthorhombic distortion. - Graphical abstract: Thermoelectric n-type CaMn{sub 0.98}W{sub 0.02}O{sub 3−δ}—Transport properties and expansion coefficient of: Oxygen loss (green region) and upper stability limit of the orthorhombic phase (yellow region) strongly affect the transport properties. Both features also cause lattice expansion, which leads to cracking of thermoelectric all-oxide converters. We report how the upper limit for applicationmore » can be shifted to even higher temperatures. - Highlights: • Level of Mn{sup 3+} at RT determines reduction behavior of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ} at HT. • Differences in Seebeck coefficient vanish at T>1200 K independent from substitution. • Substitution increases orthorhombicity of Ca{sub 1−x}A{sub x}Mn{sub 1−y}B{sub y}O{sub 3−δ}. • Linear dependence of orthorhombicity and phase stability. • Design guidelines for increase of mechanical stability of all-oxide converters.« less
Authors:
 [1] ;  [1] ;  [1] ;  [2]
  1. Laboratory Materials for Energy Conversion, Empa, Swiss Federal Laboratories for Materials Science and Technology, Überlandstr. 129, CH-8600 Dübendorf (Switzerland)
  2. Materials Chemistry, Institute for Materials Science, University of Stuttgart, Heisenbergstr. 3, DE-70569 Stuttgart (Germany)
Publication Date:
OSTI Identifier:
22499372
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Solid State Chemistry; Journal Volume: 229; Other Information: Copyright (c) 2015 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; 36 MATERIALS SCIENCE; BORATES; CALCIUM COMPOUNDS; DYSPROSIUM IONS; ELECTRICAL PROPERTIES; MANGANATES; MANGANESE IONS; MOLYBDENUM IONS; NIOBIUM IONS; N-TYPE CONDUCTORS; ORTHORHOMBIC LATTICES; PHASE STABILITY; PHASE TRANSFORMATIONS; REDOX PROCESS; SEEBECK EFFECT; TANTALUM IONS; TEMPERATURE RANGE 0400-1000 K; TUNGSTEN IONS; YTTERBIUM IONS NESDPS Office of Nuclear Energy Space and Defense Power Systems