Studies of defect clustering in CaF2: Y3+ by ionic conductivity and thermal depolarization

Jacobs, P. W. M.; Ong, S.H.

doi:10.1016/0022-3697(80)90170-5

Cited by 43 publications

(7 citation statements)

References 30 publications

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“…The fact that G(ω) saturates at the lowest dopant concentration for CaF 2 followed by SrF 2 and then BaF 2 systems could be taken as consistent with the observation that the CaF 2 host forms complex clusters at the lowest concentrations, followed by SrF 2 and then BaF 2 [31,38,39]. Since high-temperature thermal cycling is known to effect the formation of complex clusters in some fluorite mixed crystals [40][41][42][43] it provides another experimental parameter that can be varied. Of the six different systems studied here only (CaF 2 ) 1−x :(YF 3 ) x and (CaF 2 ) 1−x :(LuF 3 ) x showed a change in absorption as a result of heat treatment and the former was investigated in some detail [17].…”

Section: Influence Of Clusters On Tlssupporting

confidence: 73%

Two-level systems in fluorite mixed crystals - a far-infrared study

FitzGerald

Sievers

Campbell

2001

J. Phys.: Condens. Matter

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Low-temperature far-infrared absorption measurements have been made on six different alkaline earth:rare earth fluoride mixed crystal systems at a number of concentrations. All of these chemically disordered crystals display a glass-like continuous distribution of two-level systems (TLS) throughout the millimetre wave spectral region. Much of this study has focused on LaF3 doping where the effective density of states of the TLS initially increases with dopant concentration, reaching a maximum saturated value at a concentration of about 5 mol% for a CaF2 host, 20% for SrF2 and at least 35% for BaF2. The magnitude of the saturated TLS optical density of states is system dependent, varying from roughly one-fifth to five times that found in a standard soda-lime-silica glass. The optical strength indicates that only a small fraction, less than one in a thousand, of the dopant ions contribute to the TLS optical absorption. At submillimetre wavelengths it is found that both the fluorite mixed crystals and a standard glass exhibit a characteristic temperature-dependent absorption associated with transitions to excited levels above the ground-state TLS manifold. It is proposed that resonant phonon scattering by these excited state transitions is the cause of the plateau observed in the temperature dependence of the thermal conductivity of glasses.

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Section: Influence Of Clusters On Tlssupporting

confidence: 73%

Two-level systems in fluorite mixed crystals - a far-infrared study

FitzGerald

Sievers

Campbell

2001

J. Phys.: Condens. Matter

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“…When Ln 3+ ions are incorporated into the host lattice by substituting Zr 4+ ones, introducing extra Na + ions and forming F À vacancies in the un-occupied F À cubic sub-lattices, there are two possible mechanisms to establish the charge balance. As is well-known in the Ln 3+ -doped alkaline-earth fluoride crystals, [14][15][16][17][18][19][20][21][22] this kind of structural feature for Ln 3+ dopants easily induces the formation of Ln 3+ clusters in the Na 3 ZrF 7 host. Moreover, due to the large cation radii difference for Ln 3+ and Zr 4+ , introducing Ln 3+ ions into the Na 3 ZrF 7 lattice also results in severe structural inhomogeneity, i.e., generates Ln 3+ clusters, which has already been reported in the Ln:NaREF 4 (RE = Y, Sc) NCs.…”

mentioning

confidence: 99%

Intrinsic single-band upconversion emission in colloidal Yb/Er(Tm):Na3Zr(Hf)F7 nanocrystals

et al. 2012

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Novel Yb/Er(Tm):Na(3)MF(7) (M = Zr, Hf) nanocrystals with intrinsic single-band upconversion emission, in contrast to the routine lanthanide-doped fluoride nanocrystals which show typical multi-band upconversion emissions, are reported for the first time. Specifically, the red upconversion intensity of the Yb/Er:Na(3)ZrF(7) nanocrystals is about 5 times as high as that of the hexagonal Yb/Er:NaYF(4) ones with a similar crystal size.

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“…13 Another complication is that unintended oxygen incorporation and/or surface decomposition in samples heated above 650 °C can increase the conductivity at lower temperatures. 7 Yet, there is excellent agreement about the intrinsic conductivity at 600-900 °C, 7,8,10,16,17 and the enthalpy of anti-Frenkel disorder shows a rather high value of 2.4 eV, 13 which corresponds to weak ionic disorder and low intrinsic defect concentrations. As a result, single crystals of "undoped" CaF 2 show a low ionic conductivity of about 10 −17 S/cm at 25 °C.…”

Section: Introductionmentioning

confidence: 78%

Ion transport in nanocrystalline CaF2 films

Usiskin

Sigle

Kelsch

et al. 2021

Journal of Applied Physics

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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.

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Studies of defect clustering in CaF2: Y3+ by ionic conductivity and thermal depolarization

Cited by 43 publications

References 30 publications

Two-level systems in fluorite mixed crystals - a far-infrared study

Two-level systems in fluorite mixed crystals - a far-infrared study

Intrinsic single-band upconversion emission in colloidal Yb/Er(Tm):Na3Zr(Hf)F7 nanocrystals

Ion transport in nanocrystalline CaF2 films

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