High-temperature stability, structure and thermoelectric properties of CaMn 1 - x Nb x O 3 phases
Polycrystalline perovskite-type CaMn 1 - x Nb x O 3 phases (with x = 0.02 , 0.05 , 0.08 and 0.10) were investigated with regard to their structure, microstructure and thermal stability as a function of temperature. The studied phases revealed a complex microstructure at room temperature with 90 ° tw...
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Published in | Acta materialia Vol. 57; no. 19; pp. 5667 - 5680 |
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Main Authors | , , , , , , |
Format | Journal Article |
Language | English |
Published |
Elsevier Ltd
01.11.2009
|
Subjects | |
Online Access | Get full text |
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Summary: | Polycrystalline perovskite-type
CaMn
1
-
x
Nb
x
O
3
phases (with
x
=
0.02
,
0.05
,
0.08
and 0.10) were investigated with regard to their structure, microstructure and thermal stability as a function of temperature. The studied phases revealed a complex microstructure at room temperature with 90
°
twinned domains. At high temperatures, the manganate phases underwent a structural transition from orthorhombic to cubic symmetry, as confirmed by in situ high-temperature X-ray powder diffraction and electron diffraction data. Thermogravimetric heating/cooling studies showed a reversible thermal reduction/reoxidation process that occurred above a defined transition temperature. A possible mechanism relating the high-temperature structural transition and the thermal reduction process of slightly substituted
CaMnO
3
phases was proposed. The thermal reduction process resulted in a change in the
Mn
3
+
/
Mn
4
+
concentrations in the Mn sublattice, and therefore in a modification of the transport properties. A comprehensive study examined the impact of both phenomena on the electrical and thermal transport properties. |
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ISSN: | 1359-6454 1873-2453 |
DOI: | 10.1016/j.actamat.2009.07.062 |