In:
Journal of Applied Physics, AIP Publishing, Vol. 130, No. 10 ( 2021-09-14)
Abstract:
This work investigates the conductivity and structure of nanocrystalline CaF2 films grown at 200 °C by thermal evaporation. The in-plane conductivity is enhanced by several orders of magnitude compared to lightly doped bulk samples of CaF2, which independently confirms the finding of a previous work [Modine et al., J. Appl. Phys. 74, 2658 (1993)]. Upon heating above 200 °C, the enhancement is partially annealed out, and the activation energy increases continuously from 0.7 to 1.0 eV, which contradicts the annealing model proposed previously. The enhancement is seen only in an ∼20-nm thick region adjacent to the substrate, but this may be because the films show substantial porosity outside this region. A 5–10 nm grain size and a high density of grain boundaries are observed by high-resolution transmission electron microscopy. A 2–4 nm interfacial amorphous layer is seen in films grown on Al2O3, but such a layer is absent on MgO and evidently not responsible for the enhanced conduction. Overall, the evidence points to grain boundaries and/or dislocations as providing fast transport pathways. These results help to reconcile previous reports of enhanced ion transport in CaF2, and they are also relevant for understanding the enhancement mechanism in CaF2-based composites and antifluorite-structured materials such as Li2O.
Type of Medium:
Online Resource
ISSN:
0021-8979
,
1089-7550
Language:
English
Publisher:
AIP Publishing
Publication Date:
2021
detail.hit.zdb_id:
220641-9
detail.hit.zdb_id:
3112-4
detail.hit.zdb_id:
1476463-5
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