Tantalum and niobium diffusion in single crystalline lithium niobate

Fielitz, P.; Borchardt, G.; Ganschow, S.; Bertram, R.; Jackson, R.A.; Fritze, H.; Becker, K.-D.

Abstract

LiNbO3 and LiTaO3 are isomorphous and Nb and Ta have the same valence electron configuration and the same ionic radii. This suggests the use of Ta as a tracer to probe the self-diffusion of Nb in LiNbO3. The diffusion system consisted of a 20 nm layer of LiTaO3 sputter deposited on top of (i) a congruent LiNbO3 single crystal, i.e. (48.3 ± 0.1) mol% Li2O, and on top of (ii) a VTE processed LiNbO3 single crystal with nearly stoichiometric composition, i.e. (49.9 ± 0.1) mol% Li2O. The diffusion anneals (1000 °C ≤ T ≤ 1100 °C) were performed under a constant oxygen partial pressure of 200 mbar. From the resulting SIMS depth profiles of tantalum a constant diffusivity was extracted which can be assumed to reflect the niobium self-diffusivity in LiNbO3.

For sub-stoichiometric LiNbO3 the joint discussion of this work and of literature data on the basis of the generally accepted defect model, 4[NbLi4•] = [VLi′], suggests Nb transport in the Li sublattice. For hyper-stoichiometric LiNbO3 the defect model
is derived from the Li3NbO4/LiNbO3 solution reaction of the VTE process designed to obtain Li2O-rich LiNbO3 in accordance with the Li2O–Nb2O5 phase diagram. This model is supported by theoretical calculations of the defect formation energy. Interestingly, the migration enthalpy for the Li vacancy mediated transport of the anti-site defect NbLi4• in the Li sublattice of congruent, i.e. sub-stoichiometric, LiNbO3 is similar (within a ± 10% error) to the one derived for the Nb vacancy mediated transport of Nb in the Nb sublattice of hyper-stoichiometric LiNbO3, i.e. about 3 eV.

The significant discrepancies between our results and some earlier literature data can be consistently rationalised if the experimental procedures of those studies are carefully analysed.

Citation

Fielitz, P., Borchardt, G., Ganschow, S., Bertram, R., Jackson, R., Fritze, H., & Becker, K. (2014). Tantalum and niobium diffusion in single crystalline lithium niobate. Solid State Ionics, 259, 14-20. https://doi.org/10.1016/j.ssi.2014.02.005

• Journal Article Type: Article
• Acceptance Date: Feb 6, 2014
• Online Publication Date: Mar 4, 2014
• Publication Date: 2014-06
• Deposit Date: Jun 16, 2023
• Journal: Solid State Ionics
• Print ISSN: 0167-2738
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 259
• Pages: 14-20
• DOI: https://doi.org/10.1016/j.ssi.2014.02.005
• Keywords: Condensed Matter Physics; General Materials Science; General Chemistry
• Additional Information: This article is maintained by: Elsevier; Article Title: Tantalum and niobium diffusion in single crystalline lithium niobate; Journal Title: Solid State Ionics; CrossRef DOI link to publisher maintained version: https://doi.org/10.1016/j.ssi.2014.02.005; Content Type: article; Copyright: Copyright © 2014 Elsevier B.V. All rights reserved.