Failure of the Frenkel Defect Model to Explain the Trend in Anionic Conductivity in the MF2 Fluorite Structure and Related MSnF4 Materials

1994 ◽  
Vol 369 ◽  
Author(s):  
Georges Denes
Keyword(s):  
Fluorite Structure ◽  
Fluoride Ion ◽  
Defect Model ◽  
Fluoride Ions ◽  
Frenkel Defect ◽  
Ion Motion ◽  
Frenkel Defects ◽  
Fluorite Type ◽  
High Fluoride ◽  
Anionic Conductivity

AbstractThe high fluoride ion conductivity of fluorite type MF2 has been attributed tothe fact that half of the F8 cubes present in this structure are empty and therefore, are potential vacant sites for interstitial fluoride ions in the formation of Frenkel defects. However, the model of long range ion motion through Frenkel defects by use of empty F8 cubes is in contradiction with: (i) the little difference between the conductivities of CaF2 and BaF2, (ii) the conductivity of β-PbF2 being much larger than that of BaF2, and (iii) the much higher performance of MSnF4 even though there is no empty cube to form Frenkel defects in the MSnF4 structures.

Electrical Characterization of the Structure and Other Phenomena in Superionic PbSnF4

1995 ◽  
Vol 411 ◽  
Author(s):  
Galina Milova ◽  
Georges Denes ◽  
M. Cecilia Madamba ◽  
M. Perfiliev
Keyword(s):  
Ion Mobility ◽  
Complex Impedance ◽  
Electrical Characterization ◽  
Fold Increase ◽  
Fluoride Ion ◽  
Fluoride Ions ◽  
Covalently Bonded ◽  
Frenkel Defects ◽  
Fluorite Type

ABSTRACTThe structure of PbSnF4 is derived from that of fluorite-type β-PbF2 The replacement of half the lead by tin results in a thousand-fold increase of the fluoride ion mobility, even though tin-fluorine bonds are strongly covalent. This is due to an increase of fluoride ion disorder on some sites. The structure of α-PbSnF4 can be interpreted as resulting from the insertion of two layers of [SnF]+ cations between each pair of layers of PbF8 cubes. This has profound bearings on the texture and properties of this material, since the tin(II) stereoactive lone pairs create very effective cleavage planes. In addition, the fluorine covalently bonded to tin occupy all vacant sites used to create Frenkel defects. However, superionicity is observed by complex impedance measurements. Transport number measurements show that fluoride ions are the charge carriers.

Use of Mössbauer Spectroscopy for the Characterization of Order/Disorder Phenomena in Tin(II) Containing Ionic Conductors and for Making Predictions Regarding Possible Electron Contribution to the Conduction

1998 ◽  
Vol 548 ◽  
Author(s):  
Georges Dénès ◽  
M. Cecilia Madamba ◽  
Abdualhafeed Muntasar ◽  
Alena Peroutka ◽  
Korzior Tam ◽  
...  
Keyword(s):  
Mössbauer Spectroscopy ◽  
Mossbauer Spectroscopy ◽  
Fluorite Structure ◽  
Mixed Conductor ◽  
Fluoride Ion ◽  
Ionic Conductors ◽  
Mößbauer Spectroscopy ◽  
Electron Contribution ◽  
Fluorite Type

ABSTRACTMössbauer spectroscopy has been seldom used for the characterization of ionic conductors. However, since the introduction of divalent tin in MF2 fluorites (M = Sr, Pb and Ba) to form MSnF4, PbSn4F10 or the Pb1−xSnxF2 solid solution, all of which have structures closely related to the fluorite type, results in an enhancement of the fluoride ion conductivity by up to three orders of magnitude, and since 119 Sn is the second best Mössbauer nuclide, it seems that the Mössbauer technique could provide useful information about how tin(II) modifies the fluorite structure and leads to such a tremendous enhancement of the fluoride ion mobility. The MF2/SnF2 systems contain some number of materials that show order/disorder phenomena (between M and Sn, and also between different fluorine atoms) which make it difficult to understand them from diffraction data only. Mössbauer spectroscopy has been invaluable in helping understand the local structure at tin. By probing the valence electronic structure of tin, we can also make predictions on the possible long range mobility of the tin(II) non-bonded electron pair, which would make the material an electronic conductor or a mixed conductor.

Study of Fluoride Ion Motions in PbSnF4 and BaSnF4 Compounds With Molecular Dynamics Simulation and Solid State NMR Techniques

2000 ◽  
Vol 658 ◽  
Author(s):  
Santanu Chaudhuri ◽  
Michael Castiglione ◽  
Francis Wang ◽  
Mark Wilson ◽  
Paul A. Madden ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Solid State ◽  
Solid State Nmr ◽  
Md Simulations ◽  
Dynamics Simulation ◽  
Double Layers ◽  
Fluoride Ion ◽  
Fluoride Ions ◽  
Ion Motion ◽  
Fluorine Ions

ABSTRACTA combined approach, using solid state NMR and Molecular Dynamics (MD) simulations, has been employed in this work to investigate fluoride-ion motion in the PbSnF4 family of anionic conductors, materials that contain double layers of Sn2+ and M2+ cations. 19F MAS NMR spectra of PbSnF4 and BaSnF4 show that the fluoride ions are mobile on the NMR timescale (10−4 s), even at room temperature. In the case of BaSnF4, two different groups of fluoride ions were observed, one group corresponding to fluorine atoms between the layers of Ba2+ cations, and the other set, corresponding to mobile fluoride ions undergoing exchange between sites in the Ba-Sn and Sn-Sn layers. The 119Sn NMR suggests a highly distorted Sn environment in these compounds, consistent with the presence of stereoactive Sn lone pairs. MD simulations, using the Polarizable Ion Model, have been carried out to probe the conduction mechanism. These simulations are able to reproduce elements of the structure such as the reduction in the occupancy of the fluorine ions between the Sn-Sn layers. Anisotropic conductivity, involving primarily motion in the M-Sn layers, is predicted, consistent with the NMR results. In the case of BaSnF4, no motion involving the fluoride ions in the Ba-Ba layers is observed on the simulation timescale (10−12 s) and a cyclic mechanism of fluoride-ion motion involving two types of fluoride ions in the Ba-Sn layers is proposed.

High fluoride-ion conductivity and fluoride-ion conductor−insulator transition in fluorinated hexagonal boron nitride

2021 ◽  
Vol 21 ◽  
pp. 100523
Author(s):  
Tsuyoshi Takami ◽  
Takashi Saito ◽  
Takashi Kamiyama ◽  
Katsumi Kawahara ◽  
Toshiharu Fukunaga ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Hexagonal Boron Nitride ◽  
Insulator Transition ◽  
Ion Conductivity ◽  
Fluoride Ion ◽  
Ion Conductor ◽  
High Fluoride

scholarly journals Studies on Structural and Morphological Properties of Multidoped Ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ(x=0.2) as Solid Solutions

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Marija Stojmenović ◽  
Maja C. Pagnacco ◽  
Vladimir Dodevski ◽  
Jelena Gulicovski ◽  
Milan Žunić ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Solid Solutions ◽  
Room Temperature ◽  
Oxygen Vacancies ◽  
Room Temperature Ferromagnetism ◽  
Fluorite Structure ◽  
Lattice Parameter ◽  
Morphological Properties ◽  
Fluorite Type ◽  
Potential Improvement

The nanopowdery solid solutions of multidoped ceria Ce0.8Nd0.0025Sm0.0025Gd0.005Dy0.095Y0.095O2-δ(x=0.2) with the fluorite type crystal structure of CeO2were synthesized for the first time. Two synthesis procedures were applied: the modified glycine-nitrate procedure (MGNP method) and room temperature self-propagating reaction (SPRT method). All nanopowders were characterized by XRPD analysis, Raman spectroscopy, low temperature nitrogen physisorption, TEM, and SEM methods. According to the XRPD and Raman spectroscopy results, single phase solid solutions of fluorite structure were evidenced regardless of the number of dopants and synthesis procedure. Both XRPD and TEM were analyses evidenced nanometer particle dimensions. The SPRT method results in obtaining sample with higher specific surface area, smaller crystallite and particles sizes, and the same values of the lattice parameter in comparison to pure CeO2. Raman spectroscopy was confirmed to the oxygen vacancies introduced into the ceria lattice when Ce4+ions were replaced with cations (dopants) of lower valence state (3+), which may indicate the potential improvement of ionic conductivity. Additionally, the presence of oxygen vacancies in the lattice ceria, as well as very developed grain boundaries, gives a new possibility for potential application of obtained nanopowders in the area of room temperature ferromagnetism as spintronics.

Si-corrole-based fluoride fluorometric turn-on sensor

2020 ◽  
Vol 24 (05n07) ◽  
pp. 929-937
Author(s):  
Ewa Jaworska ◽  
Fabrizio Caroleo ◽  
Corrado Di Natale ◽  
Krzysztof Maksymiuk ◽  
Roberto Paolesse ◽  
...  
Keyword(s):  
Optical Sensors ◽  
Linear Dependence ◽  
Porous Membrane ◽  
Ion Concentration ◽  
Fluoride Ion ◽  
Fluoride Ions ◽  
Acidic Solutions ◽  
Turn On ◽  
New Type ◽  
Receptor Layer

We present here a new type of fluoride ion optode, constituted by a highly lipophilic PVDF porous membrane modified with a liquid receptor layer containing the emission-active Si corrole F[Formula: see text] selective ionophore. For the optimized composition of the receptor layer, in acidic solutions an increase of Si-corrole emission was observed by increasing fluoride ion concentration, a behavior different from most porphyrinoid-based optical sensors. An observed linear dependence of the Si corrole emission intensity (read at 635 nm) was within the range 10[Formula: see text] to 10[Formula: see text] M of fluoride ions.

scholarly journals Mechanical and Functional Properties of a Novel Apatite-Ionomer Cement for Prevention and Remineralization of Dental Caries

Materials ◽  
2019 ◽  
Vol 12 (23) ◽  
pp. 3998 ◽  
Author(s):  
Rie Imataki ◽  
Yukari Shinonaga ◽  
Takako Nishimura ◽  
Yoko Abe ◽  
Kenji Arita
Keyword(s):  
Fracture Toughness ◽  
Functional Properties ◽  
Glass Ionomer Cement ◽  
Pediatric Dentistry ◽  
Cement Matrix ◽  
Fluoride Ion ◽  
Ion Release ◽  
Fluoride Ions ◽  
Acid Buffer ◽  
Ionomer Cement

Especially in pediatric dentistry, prevention by the control of initial lesions prior to cavitation is very important, and application of a pit and fissure sealant is essential to achieve this. Numerous reports have suggested that resin-based sealants are inferior to sealants based on glass-ionomer cement (GIC), because of GIC’s many advantages, such as fluoride ion release properties and its good adhesion to tooth structures. However, the use of GIC is impeded due to its low flexural strength and fracture toughness. In this paper, we developed and characterized an apatite-ionomer cement (AIC) that incorporates hydroxyapatite (HAp) into the GIC; this development was aimed at not only reinforcing the flexural and compressive strength but also improving some functional properties for the creation of the material suitable for sealant. We examined the influence of differences in the compounding conditions of GIC powder, liquid, and HAp on flexural and compressive strengths, fracture toughness, fluoride ion release property, shear bond strength to bovine enamel, surface pH of setting cements, and acid buffer capability. These methods were aimed at elucidating the reaction mechanism of porous spherical-shaped HAp (HApS) in AIC. The following observations were deduced. (1) HAp can improve the mechanical strengths of AIC by strengthening the cement matrix. (2) The functional properties of AIC, such as acid buffer capability, improved by increasing the releasing amounts of various ions including fluoride ions. The novel AIC developed in this study is a clinically effective dental material for prevention and remineralization of tooth and initial carious lesion.

scholarly journals Ratiometric sensing of fluoride ions using Raman spectroscopy

2020 ◽  
Vol 56 (92) ◽  
pp. 14463-14466
Author(s):  
William J. Tipping ◽  
Liam T. Wilson ◽  
Sonja K. Blaseio ◽  
Nicholas C. O. Tomkinson ◽  
Karen Faulds ◽  
...  
Keyword(s):  
Raman Spectroscopy ◽  
Fluoride Ion ◽  
Ion Detection ◽  
Fluoride Ions ◽  
Ratiometric Sensing ◽  
Ratiometric Sensor

A simple ratiometric sensor based on Raman spectroscopy enables rapid fluoride ion detection in a paper-based assay using a portable spectrometer.

scholarly journals Fluoride ion adsorption from wastewater using magnesium(II), aluminum(III) and titanium(IV) modified natural zeolite: kinetics, thermodynamics, and mechanistic aspects of adsorption

2017 ◽  
Vol 8 (4) ◽  
pp. 479-489 ◽  
Author(s):  
Zhijun Ma ◽  
Qi Zhang ◽  
Xingyuan Weng ◽  
Changye Mang ◽  
Liwei Si ◽  
...  
Keyword(s):  
Natural Zeolite ◽  
Adsorption Process ◽  
Fluoride Ion ◽  
Ion Adsorption ◽  
Order Model ◽  
Fluoride Ions ◽  
Modified Zeolite ◽  
Fluoride Adsorption ◽  
Pseudo Second Order ◽  
Modified Zeolites

Abstract Natural zeolite was modified using metal ions, including magnesium(II), aluminum(III) and titanium(IV). The modified zeolite was then used as an adsorbent for the investigation of the adsorption kinetics, isotherms, and thermodynamic parameters of fluoride ions in wastewater at various pHs and temperatures. The kinetics and thermodynamics for the removal of the fluoride ions onto the modified zeolite have also been investigated. The fluoride ion adsorption capacity of the three types of modified zeolites exhibited an increase, then decrease, with rising pH. The fluoride adsorption capacity of the modified zeolites decreased with an increase in temperature. The pseudo-second-order model is more suitable for describing the adsorption kinetic data than the pseudo-first-order model for modified zeolite and the adsorption process of the fluoride ions reveals pseudo-second-order kinetic behavior, respectively. It was found that the adsorption equilibrium data fit the Freundlich isothermal equation better than that of the Langmuir isothermal and Dubinin–Radushkevich (D–R) isothermal equations. Thermodynamic analysis suggests that the negative values of ΔG0 and ΔH0 further indicate that the fluoride adsorption process is both spontaneous and exothermic. The results of competitive adsorption tests suggest that the modified metal zeolite materials adsorb fluoride ions with high selectivity.

Purification of Water from Fluoride Ions by a Lanthanum-Containing Ceramic Material

2018 ◽  
Vol 22 (8) ◽  
pp. 28-31 ◽  
Author(s):  
V.Yu. Chukhlanov ◽  
O.G. Selivanov ◽  
E.S. Pikalov ◽  
C.M. Chesnokova ◽  
A.A. Podolets
Keyword(s):  
Ceramic Material ◽  
Mechanical Characteristics ◽  
Binding Capacity ◽  
Environmental Safety ◽  
Fluoride Ion ◽  
Ion Content ◽  
Fluoride Ions ◽  
Phosphate Ions ◽  
Environmentally Safe ◽  
Purification Of Water

Studies have been carried out to create a lanthanum-containing ceramic material that can be used to purify water from fluoride ions. A composition was developed for the preparation of a ceramic material, the physico-mechanical characteristics of its samples were determined, and their binding capacity to fluoride ions was investigated. There was researched environmental safety of a material. It is proved that when 6% by weight of lanthanum carbonate is added to the charge, an environmentally safe material for cleaning aqueous systems with a fluoride ion content of up to 10 mg/l can be obtained. It has been established that this material can be used with sufficient efficiency to purify water from phosphate ions.

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