The effects of boule to boule compositional variations on the properties of LiNbO3 electro-optic devices—an interpretation from defect chemistry studies

Holmes, Rohan; Minford, W. J.

doi:10.1080/00150198708008210

Cited by 24 publications

(6 citation statements)

References 13 publications

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“…In contrast to the opinion of Sugak et al, reduction-oxidation cycles are not completely reversible processes due to possible Li oxide loss especially at higher temperatures and in closely stoichiometric LiNbO 3 , the latter being also much more resistant to reduction. Thermal reduction was shown to increase off-stoichiometry which, in turn, leads to larger density [37,38], quantitatively supporting Equation (2). All this gives full support to the cationic model of coloration excluding any diffusion of oxygen in the bulk.…”

Section: Discussion Of the Mechanochemical Reaction Including Redox Psupporting

confidence: 61%

Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling

et al. 2019

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Lithium niobate (LiNbO3, LN) nanocrystals were prepared by ball-milling of the crucible residue of a Czochralski grown congruent single crystal, using a Spex 8000 Mixer Mill with different types of vials (stainless steel, alumina, tungsten carbide) and various milling parameters. Dynamic light scattering and powder X-ray diffraction were used to determine the achieved particle and grain sizes, respectively. Possible contamination from the vials was checked by energy-dispersive X-ray spectroscopy measurements. Milling resulted in sample darkening due to mechanochemical reduction of Nb (V) via polaron and bipolaron formation, oxygen release and Li2O segregation, while subsequent oxidizing heat-treatments recovered the white color with the evaporation of Li2O and crystallization of a LiNb3O8 phase instead. The phase transformations occurring during both the grinding and the post-grinding heat treatments were studied by Raman spectroscopy, X-ray diffraction and optical reflection measurement, while the Li2O content of the as-ground samples was quantitatively measured by coulometric titration.

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Section: Discussion Of the Mechanochemical Reaction Including Redox Psupporting

confidence: 61%

Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling

et al. 2019

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“…Although point defects are indispensable to properly describe congruent, i.e., Li-deficient, LiNbO 3 , it is still not conclusively established which kinds of defects occur in which concentrations. While oxygen vacancies are practically excluded [15][16][17][18], different cation-substitution models are possible [19]. Seemingly, the simplest way to achieve the observed Li:Nb ratio, originally proposed by Lerner et al [17], is given by Nb Li antisite defects, where a Li atom is substituted by a Nb atom as shown in Fig.…”

Section: Introductionmentioning

confidence: 99%

Free and defect-bound (bi)polarons inLiNbO3: Atomic structure and spectroscopic signatures fromab initiocalculations

Schmidt

Kozub

Biktagirov

et al. 2020

Phys. Rev. Research

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Polarons in dielectric crystals play a crucial role for applications in integrated electronics and optoelectronics. In this work, we use density-functional theory and Green's function methods to explore the microscopic structure and spectroscopic signatures of electron polarons in lithium niobate (LiNbO 3). Total-energy calculations and the comparison of calculated electron paramagnetic resonance data with available measurements reveal the formation of bound polarons at Nb Li antisite defects with a quasi-Jahn-Teller distorted, tilted configuration. The defect-formation energies further indicate that (bi)polarons may form not only at Nb Li antisites but also at structures where the antisite Nb atom moves into a neighboring empty oxygen octahedron. Based on these structure models, and on the calculated charge-transition levels and potential-energy barriers, we propose two mechanisms for the optical and thermal splitting of bipolarons, which provide a natural explanation for the reported two-path recombination of bipolarons. Optical-response calculations based on the Bethe-Salpeter equation, in combination with available experimental data and new measurements of the optical absorption spectrum, further corroborate the geometries proposed here for free and defect-bound (bi)polarons.

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“…This explains the Li-deficient character of LiNbO 3 accommodated by lithium vacancies (V Li ) and Nb Li antisites (Nb on Li site) requiring small formation energies. Compared to compensation involving anion vacancies at larger costs [13,14], compensation only by cationic disorder requires no additional volume and leads to the observed larger density of cLN compared to sLN (stoichiometric LN) [15][16][17][18][19]. Another characteristic property of LN is the high mobility of Li + ions observable already at temperatures near 350 • C (see [9,[20][21][22] and references therein).…”

Section: Structure and Charge Compensation Mechanismmentioning

confidence: 99%

‘Horror Vacui’ in the Oxygen Sublattice of Lithium Niobate Made Affordable by Cationic Flexibility

Corradi

Kovács

2021

Crystals

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The present review is intended to interest a broader audience interested in the resolution of the several decades-long controversy on the possible role of oxygen-vacancy defects in LiNbO3. Confronting ideas of a selected series of papers from classical experiments to brand new large-scale calculations, a unified interpretation of the defect generation and annealing mechanisms governing processes during thermo- and mechanochemical treatments and irradiations of various types is presented. The dominant role of as-grown and freshly generated Nb antisite defects as traps for small polarons and bipolarons is demonstrated, while mobile lithium vacancies, also acting as hole traps, are shown to provide flexible charge compensation needed for stability. The close relationship between LiNbO3 and the Li battery materials LiNb3O8 and Li3NbO4 is pointed out. The oxygen sublattice of the bulk plays a much more passive role, whereas oxygen loss and Li2O segregation take place in external or internal surface layers of a few nanometers.

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The effects of boule to boule compositional variations on the properties of LiNbO3 electro-optic devices—an interpretation from defect chemistry studies

Cited by 24 publications

References 13 publications

Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling

Mechanochemical Reactions of Lithium Niobate Induced by High-Energy Ball-Milling

Free and defect-bound (bi)polarons inLiNbO3: Atomic structure and spectroscopic signatures fromab initiocalculations

‘Horror Vacui’ in the Oxygen Sublattice of Lithium Niobate Made Affordable by Cationic Flexibility

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