Center for Electronic Microscopy and Analysis

Columbus, OH, United States

Center for Electronic Microscopy and Analysis

Columbus, OH, United States
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Jeric M.,Jozef Stefan Institute | Jeric M.,Jožef Stefan International Postgraduate School | de Boor J.,German Aerospace Center | Zavasnik J.,Center for Electronic Microscopy and Analysis | And 2 more authors.
Journal of Materials Science | Year: 2016

Excess SrO and CaO were added to the Sr(Ti0.8Nb0.2)O3 thermoelectric material, which was structurally compensated by the formation of Ruddlesden–Popper-type planar faults with the compositions SrO and/or (Sr, Ca)O. Both types of doping significantly changed the original isotropic Sr(Ti0.8Nb0.2)O3 microstructure and resulted in the formation of lamellar Ruddlesden–Popper-type phases within the Sr(Ti0.8Nb0.2)O3 grains. Three-dimensional networks of single Ruddlesden–Popper-type faults were also observed in the Sr(Ti0.8Nb0.2)O3 for both types of doping. The combination of both structural features significantly lowered the thermal conductivity in comparison with Sr(Ti0.8Nb0.2)O3 due to the enhanced phonon scattering observed at the planar faults, which proves that introducing such defects is a promising method for lowering the thermal conductivity of the Sr(Ti0.8Nb0.2)O3 thermoelectric material. The highest figure of merit (ZT = 0.08) was achieved with CaO doping, since the significantly reduced thermal conductivity was accompanied by an increased power factor. © 2016, Springer Science+Business Media New York.


Loretto M.H.,University of Birmingham | Phillips P.J.,Center for Electronic Microscopy and Analysis | Phillips P.J.,University of Illinois at Chicago | Mills M.J.,Center for Electronic Microscopy and Analysis
Scripta Materialia | Year: 2015

Mechanisms for the formation of stacking fault tetrahedra in metals are critically reviewed in the light of recent observations, where it is claimed, incorrectly, that for the first time stacking fault tetrahedra have been observed, which are formed by a dislocation mechanism, without the involvement of vacancies. In this note the experimental conditions where stacking fault tetrahedra have been observed are defined, together with the mechanisms that have been put forward to explain the observations. Three fundamentally different mechanisms are identified. © 2014 Acta Materialia Inc.


Loretto M.H.,University of Birmingham | Phillips P.J.,Center for Electronic Microscopy and Analysis | Mills M.J.,Center for Electronic Microscopy and Analysis
Scripta Materialia | Year: 2014

Mechanisms for the formation of stacking fault tetrahedra in metals are critically reviewed in the light of recent observations, where it is claimed, incorrectly, that for the first time stacking fault tetrahedra have been observed, which are formed by a dislocation mechanism, without the involvement of vacancies. In this note the experimental conditions where stacking fault tetrahedra have been observed are defined, together with the mechanisms that have been put forward to explain the observations. Three fundamentally different mechanisms are identified. © 2014 Acta Materialia Inc.

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