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 -