Details
| Original language | English |
|---|---|
| Pages (from-to) | 6225-6229 |
| Number of pages | 5 |
| Journal | Chemistry - a European journal |
| Volume | 18 |
| Issue number | 20 |
| Publication status | Published - 14 May 2012 |
Abstract
By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent "dopants" can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state-of-the-art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF 2 lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF 2 phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF 2-BaF 2 multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge-transfer that occurred at the hetero-interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher-dimensional doping) to homogeneous doping (zero-dimensional doping).
Keywords
- charge transfer, doping, interfaces, ion conductors, molecular modeling
ASJC Scopus subject areas
- Chemical Engineering(all)
- Catalysis
- Chemistry(all)
- Organic Chemistry
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In: Chemistry - a European journal, Vol. 18, No. 20, 14.05.2012, p. 6225-6229.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - From composites to solid solutions
T2 - Modeling of ionic conductivity in the CaF 2-BaF 2 system
AU - Zahn, Dirk
AU - Heitjans, Paul
AU - Maier, Joachim
PY - 2012/5/14
Y1 - 2012/5/14
N2 - By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent "dopants" can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state-of-the-art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF 2 lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF 2 phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF 2-BaF 2 multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge-transfer that occurred at the hetero-interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher-dimensional doping) to homogeneous doping (zero-dimensional doping).
AB - By using calcium fluorite and barium fluorite as test materials, we demonstrated that homovalent "dopants" can greatly affect ionic conductivity through locally changing the defect density. Whilst this doping is a state-of-the-art effect in the case of dopants that replace native ions of different charge (heterovalent dopants), it is a rather surprising effect at a first glance for substitutional dopants of the same charge; here, the phenomenon is not electrostatic, but elastic in nature. As a consequence of size mismatch, the smaller Ca atoms in the BaF 2 lattice favored the formation of interstitial sites that were located close to the Ca atoms, whilst doping larger Ba species into the CaF 2 phase favored vacancy formation. In terms of conductivity, and in agreement with the different mobilities, the first doping effect was favorable, whilst the other decreased conductivity. The concentration effects were formalized by a heterogeneous Frenkel reaction that was distinguished from the mean Frenkel reaction by additional (elastic) trapping that became more pronounced the lower the temperature. It was very revealing to relate this phenomenon to CaF 2-BaF 2 multilayers and composites. In very general terms, these effects in the solid solutions were understood as being the atomistic limit of the interfacial charge-transfer that occurred at the hetero-interface of the crystallites or films, and reflected the transition from heterogeneous doping (higher-dimensional doping) to homogeneous doping (zero-dimensional doping).
KW - charge transfer
KW - doping
KW - interfaces
KW - ion conductors
KW - molecular modeling
UR - http://www.scopus.com/inward/record.url?scp=84860740485&partnerID=8YFLogxK
U2 - 10.1002/chem.201102410
DO - 10.1002/chem.201102410
M3 - Article
AN - SCOPUS:84860740485
VL - 18
SP - 6225
EP - 6229
JO - Chemistry - a European journal
JF - Chemistry - a European journal
SN - 0947-6539
IS - 20
ER -