Details
| Original language | English |
|---|---|
| Article number | 115355 |
| Journal | Solid State Ionics |
| Volume | 352 |
| Early online date | 6 Jun 2020 |
| Publication status | Published - Sept 2020 |
Abstract
Defects of various types in crystalline and nanocrystalline materials govern a range of electrical, optical and mechanical properties. In particular, they are at the heart of translational ion dynamics in solid electrolytes. One of the most prominent examples revealing a drastic increase in ionic conductivity σDC by several orders of magnitude when going from an ordered crystalline matrix to a structurally disordered one is lithium tantalate. Here, structurally disordered, nanocrystalline LiTaO3 served as a model substance to shed light on the question to what extent the degree of disorder decreases upon annealing an originally defect-rich oxide. Disorder can be introduced by high-energy ball milling of LiTaO3 crystallites with diameters in the μm range. Broadband conductivity spectroscopy, EXAFS and positron annihilation lifetime spectroscopy were used to correlate ion transport properties with interatomic distances, bond distortions and positron lifetimes. It turned out that milling times of only 30 min are sufficient to generate a highly defective oxide. Upon annealing at temperatures of T = 200 °C the defects can almost be preserved. Annealing at 750 °C for 1 h is needed to induce healing of the defects. Although we observe a recovery of the original interatomic distances and an increase in activation energy Ea for ionic transport from 0.75 eV to 0.81 eV, the initial transport properties of the unmilled sample (0.97 eV) cannot be fully restored. Most interestingly, the change in Ea is accompanied by a change of the entropy-controlled Arrhenius pre-factor governing the temperature dependence of σDCT. Moreover, positron lifetimes remain high in the annealed samples. Hence, our results point to samples with fewer distortions but still rich in vacancy-type defects. Altogether, the combination of ball milling and annealing helps adjust ionic conductivities in LiTaO3 to vary over 4 to 5 orders of magnitude.
Keywords
- Defects, EXAFS, Ionic conductivity, Lithium tantalate, Positron lifetime spectroscopy
ASJC Scopus subject areas
- Chemistry(all)
- General Chemistry
- Materials Science(all)
- General Materials Science
- Physics and Astronomy(all)
- Condensed Matter Physics
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In: Solid State Ionics, Vol. 352, 115355, 09.2020.
Research output: Contribution to journal › Article › Research › peer review
}
TY - JOUR
T1 - Influence of defects on ionic transport in LiTaO3
T2 - A study using EXAFS and positron annihilation lifetime spectroscopy
AU - Gadermaier, B.
AU - Resch, L.
AU - Pickup, D. M.
AU - Hanghofer, I.
AU - Hanzu, I.
AU - Heitjans, Paul
AU - Sprengel, W.
AU - Würschum, R.
AU - Chadwick, A. V.
AU - Wilkening, H. M. R.
N1 - Funding Information: Financial support by the Deutsche Forschungsgemeinschaft (DFG) in the frame of the Research Unit 1277, grant no. WI3600/2-1(4-1) (FOR1277)) as well as by the Austrian Federal Ministry of Science, Research and Economy , and the Austrian National Foundation for Research, Technology and Development (Christian Doppler Laboratory of Lithium Batteries: Ageing Effects, Technology and New Materials) is greatly appreciated. Furthermore, we thank the Österreichische Forschungs-Förderungsgesellschaft (FFG) in the frame of the K project safe battery.
PY - 2020/9
Y1 - 2020/9
N2 - Defects of various types in crystalline and nanocrystalline materials govern a range of electrical, optical and mechanical properties. In particular, they are at the heart of translational ion dynamics in solid electrolytes. One of the most prominent examples revealing a drastic increase in ionic conductivity σDC by several orders of magnitude when going from an ordered crystalline matrix to a structurally disordered one is lithium tantalate. Here, structurally disordered, nanocrystalline LiTaO3 served as a model substance to shed light on the question to what extent the degree of disorder decreases upon annealing an originally defect-rich oxide. Disorder can be introduced by high-energy ball milling of LiTaO3 crystallites with diameters in the μm range. Broadband conductivity spectroscopy, EXAFS and positron annihilation lifetime spectroscopy were used to correlate ion transport properties with interatomic distances, bond distortions and positron lifetimes. It turned out that milling times of only 30 min are sufficient to generate a highly defective oxide. Upon annealing at temperatures of T = 200 °C the defects can almost be preserved. Annealing at 750 °C for 1 h is needed to induce healing of the defects. Although we observe a recovery of the original interatomic distances and an increase in activation energy Ea for ionic transport from 0.75 eV to 0.81 eV, the initial transport properties of the unmilled sample (0.97 eV) cannot be fully restored. Most interestingly, the change in Ea is accompanied by a change of the entropy-controlled Arrhenius pre-factor governing the temperature dependence of σDCT. Moreover, positron lifetimes remain high in the annealed samples. Hence, our results point to samples with fewer distortions but still rich in vacancy-type defects. Altogether, the combination of ball milling and annealing helps adjust ionic conductivities in LiTaO3 to vary over 4 to 5 orders of magnitude.
AB - Defects of various types in crystalline and nanocrystalline materials govern a range of electrical, optical and mechanical properties. In particular, they are at the heart of translational ion dynamics in solid electrolytes. One of the most prominent examples revealing a drastic increase in ionic conductivity σDC by several orders of magnitude when going from an ordered crystalline matrix to a structurally disordered one is lithium tantalate. Here, structurally disordered, nanocrystalline LiTaO3 served as a model substance to shed light on the question to what extent the degree of disorder decreases upon annealing an originally defect-rich oxide. Disorder can be introduced by high-energy ball milling of LiTaO3 crystallites with diameters in the μm range. Broadband conductivity spectroscopy, EXAFS and positron annihilation lifetime spectroscopy were used to correlate ion transport properties with interatomic distances, bond distortions and positron lifetimes. It turned out that milling times of only 30 min are sufficient to generate a highly defective oxide. Upon annealing at temperatures of T = 200 °C the defects can almost be preserved. Annealing at 750 °C for 1 h is needed to induce healing of the defects. Although we observe a recovery of the original interatomic distances and an increase in activation energy Ea for ionic transport from 0.75 eV to 0.81 eV, the initial transport properties of the unmilled sample (0.97 eV) cannot be fully restored. Most interestingly, the change in Ea is accompanied by a change of the entropy-controlled Arrhenius pre-factor governing the temperature dependence of σDCT. Moreover, positron lifetimes remain high in the annealed samples. Hence, our results point to samples with fewer distortions but still rich in vacancy-type defects. Altogether, the combination of ball milling and annealing helps adjust ionic conductivities in LiTaO3 to vary over 4 to 5 orders of magnitude.
KW - Defects
KW - EXAFS
KW - Ionic conductivity
KW - Lithium tantalate
KW - Positron lifetime spectroscopy
UR - http://www.scopus.com/inward/record.url?scp=85085842174&partnerID=8YFLogxK
U2 - 10.1016/j.ssi.2020.115355
DO - 10.1016/j.ssi.2020.115355
M3 - Article
AN - SCOPUS:85085842174
VL - 352
JO - Solid State Ionics
JF - Solid State Ionics
SN - 0167-2738
M1 - 115355
ER -