beta-radiation detected NMR signals of 8Li nuclei have been observed in 7Li2S and 7Li2O. By doubl... more beta-radiation detected NMR signals of 8Li nuclei have been observed in 7Li2S and 7Li2O. By double frequency irradiation the dipolar linewidth of the 8Li NMR signal was suppressed and lines as narrow as 32 Hz were obtained being among the narrowest ever obtained in solids. This allowed the determination of the 7,8Li hyperfine structure anomaly 7Delta8 = -7.3(1.9) × 10-5.
ABSTRACT Self-diffusion in solid Li was studied via the spin-lattice relaxation of polarised radi... more ABSTRACT Self-diffusion in solid Li was studied via the spin-lattice relaxation of polarised radioactive 8Li nuclei using their asymmetric beta -decay radiation. The diffusion-induced spin-lattice relaxation rate 1/T1diff was measured as a function of temperature from the melting point Tm=454K down to about 1/2Tm and as a function of the magnetic field from 8 to 700 mT. 1/T1diff can be explained assuming the nuclear dipole-dipole interaction alone. The data are analysed in the frame of the encounter model of correlated self-diffusion. The macroscopic self-diffusion coefficient DSD is determined over almost seven decades. A deviation from Arrhenius behaviour at elevated temperatures is interpreted in terms of a combined monovacancy/divacancy (1V/2V) mechanism. The correlation factor obtained from DSD and tracer self-diffusion coefficients DT, measured by mass spectroscopy, has a temperature dependence which is consistent with the 1V/2V model. The question of the possible existence of a non-classical isotope effect cannot be settled by a comparison of the present DSD values with those known from conventional nuclear magnetic resonance on 7Li.
Nuclear magnetic resonance measurements were carried out on neutron activated 20F(T1/2=11s) nucle... more Nuclear magnetic resonance measurements were carried out on neutron activated 20F(T1/2=11s) nuclei in a single crystal of KZnF3. The quadrupolar splitted NMR spectrum, detected via the 20F β-radiation asymmetry, could be observed using a radio frequency modulation technique. The quadrupole coupling constant was determined to e2 q Q/h= + (12.0 ± 1.5) MHz at room temperature. The sign of e2 q Q was obtained from a simultaneous γ-ray anisotropy measurement on the succeeding 20Ne transition. Utilising a calculated field gradient of the fluorine atom, an fQ = 4.6% is determined. This value is compared with literature data of similar compounds.
Solid state physics experiments were conducted on systems belonging to different substance classe... more Solid state physics experiments were conducted on systems belonging to different substance classes. Polarized radioactive probe nuclei were obtained in sample material by activation with spin-polarized thermal reactor neutrons. The decay radiation allows for the determination of nuclear resonance signals as well as die-away curves of the nucleus polarization by spin-lattice relaxation processes. The method was applied to ionic crystals, semiconductors, glasses, and metal melts. Dynamics and structure of intrinsics, radiation and doping effects, self diffusion and electronic properties are determined.
Owing to the structural flexibility of spinels, providing a wide range of physical and chemical b... more Owing to the structural flexibility of spinels, providing a wide range of physical and chemical behavior, these materials have been considered as a convenient model system for the investigation of the size dependent properties of complex ionic systems. In this work, quantitative information is obtained on the crystallite size dependent ionic configuration in nanosized spinel oxides prepared by mechanochemical processing of the corresponding bulk materials. Experimentally determined values of the crystallite size and of the mean degree of inversion of nanostructured spinels are used to calculate the volume fraction of interfaces/surfaces and their thickness in the nanomaterials.
TiO2 photocatalysts with predetermined phase composition (anatase-to-rutile ratio) have been prep... more TiO2 photocatalysts with predetermined phase composition (anatase-to-rutile ratio) have been prepared from strongly acidic aqueous HCl/TiCl4 mixtures with 0.1M≤[HCl]TOT≤5M and 0.05M≤[TiCl4]TOT≤3M (where the subscript TOT denotes total or analytical concentration). During the syntheses, TiCl4 was added to a cold-HCl solution. The initially precipitate free reaction mixture was boiled, resulting in the formation of large amount of solid, nanocrystalline (particle size
Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its a... more Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its application as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Nevertheless, diffusion in Li3N was studied by many groups and various techniques (see [1-3] and references therein) which predestines it to act as a model system for the establishment of new techniques. Li3N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li2N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li2N layer and Li(1) in the Li layer. Li diffusion in the Li2N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the caxis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions ca...
Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its a... more Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its application as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Nevertheless, diffusion in Li3N was studied by many groups and various techniques (see [1-3] and references therein) which predestines it to act as a model system for the establishment of new techniques. Li3N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li2N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li2N layer and Li(1) in the Li layer. Li diffusion in the Li2N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the caxis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions ca...
Sustainable energy storage in the form of secondary Li ion batteries requires both the preparatio... more Sustainable energy storage in the form of secondary Li ion batteries requires both the preparation of advanced materials as well as the development of techniques being capable to characterize the transport properties of ionic conductors preferably on large time and length scales. By combining the various techniques of nuclear magnetic resonance (NMR) [1], which, in particular, include the generation and analysis of stimulated echoes, Li jump rates with values ranging from a few jumps per second up to rates of the order of some millions of jumps per millisecond can be studied [2-4]. In Fig. 1 an overview of the time windows accessible by various NMR techniques is given [2-4].
Sustainable energy storage in the form of secondary Li ion batteries requires both the preparatio... more Sustainable energy storage in the form of secondary Li ion batteries requires both the preparation of advanced materials as well as the development of techniques being capable to characterize the transport properties of ionic conductors preferably on large time and length scales. By combining the various techniques of nuclear magnetic resonance (NMR) [1], which, in particular, include the generation and analysis of stimulated echoes, Li jump rates with values ranging from a few jumps per second up to rates of the order of some millions of jumps per millisecond can be studied [2-4]. In Fig. 1 an overview of the time windows accessible by various NMR techniques is given [2-4].
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In order to improve our understanding of the transport mechanisms of lithium in glasses, we have ... more In order to improve our understanding of the transport mechanisms of lithium in glasses, we have performed diffusion and ionic conductivity studies on spodumene composition (LiAlSi 2 O 6) glasses. In diffusion couple experiments pairs of chemically identical glasses with different lithium isotopy (natural Li vs pure 7 Li) were processed at temperatures between 482 and 732 K. Profiles of lithium isotopes were measured after the diffusion runs innovatively applying femtosecond UV laser ablation combined with inductively coupled plasma mass spectrometry (LA ICP-MS). Self-diffusion coefficients of lithium in the glasses were determined by fitting the isotope profiles. During some of the diffusion experiments the electrical conductivity of the samples was intermittently measured by impedance spectrometry. Combining ionic conductivity and self-diffusivity yields a temperature-independent correlation factor of ∼0.50, indicating that motions of Li ions are strongly correlated in this type of glasses. Lithium self-diffusivity in LiAlSi 2 O 6 glass was found to be very similar to that in lithium silicate glasses although Raman spectroscopy demonstrates structural differences between these glasses; that is, the aluminosilicate is completely polymerized while the lithium silicate glasses contain large fractions of nonbridging oxygen.
A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the ... more A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the synthesis of Li 3 MF 6-type and Li 2 MF 5-type compounds. It is based on a fluorolytic process using transition metal acetylacetonates as precursors. The domain size of the obtained powders can be controlled by modifying the conditions of synthesis. 6 Li and 7 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is used to study local environments of the Li ions in orthorhombic and monoclinic Li 3 VF 6 as well as Li 2 MnF 5. The number of magnetically inequivalent Li sites found by MAS NMR is in agreement with the respective crystal structure of the compounds studied. Quantum chemical calculations show that all materials have high de-lithiation energies making them suitable candidates to be used as high-voltage battery cathode materials.
Within the system Li2O – TiO2, lithium hexatitanate Li2Ti6O13 (i.e. Li2O ∙ 6 TiO2) was already st... more Within the system Li2O – TiO2, lithium hexatitanate Li2Ti6O13 (i.e. Li2O ∙ 6 TiO2) was already studied before by electrochemical methods with respect to its application as a potential Li-ion battery anode material [1, 2]. This compound is also attractive for fundamental cation diffusion studies, in particular due to its channel structure and the fact that Li and Na are interchangeable. The present work examines the effect of different Li : Na ratios in LixNa2-xTi6O13 on diffusion using impedance spectroscopy which measures the conductivity over a wide frequency range and thus on different length scales. This also enables the comparison with NMR results obtained by us in a separate study. Additionally, the Hebb-Wagner polarization (DC polarization) method is being used here to discriminate between the cation and a partial electronic conductivity [3].
Pulsed field gradient (PFG) NMR is applied to measure self-diffusion coefficients of 1,3,5 triiso... more Pulsed field gradient (PFG) NMR is applied to measure self-diffusion coefficients of 1,3,5 triisopropyl-benzene in the particles of several industrial FCC catalysts having different systems of mesoand macropores. Relating these diffusivities to the self-diffusion coefficient of 1,3,5 tri-isopropyl-benzene in the liquid phase, the tortuosity factors for diffusion in the mesoand macropores of the particles were obtained. The values of the tortuosity factors were found to increase with a increasing volumetric fraction of the small (< 20 nm) mesoand macropores in the total intraparticle volume.
Dedicated to Professor Werner MüllerWarmuth on the occasion of his 65th birthday Investigations o... more Dedicated to Professor Werner MüllerWarmuth on the occasion of his 65th birthday Investigations of Li diffusion in stage-1 and stage-2 Li graphite intercalation compounds with neutron time-of-flight and backscattering techniques and ^-radiation detected nuclear magnetic resonance/relaxation (/J-NMR) with the nucleus 8Li(T1/2 = 0.8 s) are reviewed and compared. De pending on temperature, the spin-lattice relaxation-rate T{1 of 8Li is governed by different pro cesses. Above 300 K, Tf1 (T) shows maxima induced by long-range Li+ diffusion. Jump correlation times are estimated. Inspection of the B field dependence of T f1 revealed two-dimensional diffusion behaviour. The neutron spectra showed a quasielastic line broadening above 500 K, which was used to obtain diffusion coefficients and to trace jump vectors of the in-plane motion. The diffusion parameters observed with both techniques are compared, and differences that show up are dis cussed. In addition, the low-temperature spin-la...
beta-radiation detected NMR signals of 8Li nuclei have been observed in 7Li2S and 7Li2O. By doubl... more beta-radiation detected NMR signals of 8Li nuclei have been observed in 7Li2S and 7Li2O. By double frequency irradiation the dipolar linewidth of the 8Li NMR signal was suppressed and lines as narrow as 32 Hz were obtained being among the narrowest ever obtained in solids. This allowed the determination of the 7,8Li hyperfine structure anomaly 7Delta8 = -7.3(1.9) × 10-5.
ABSTRACT Self-diffusion in solid Li was studied via the spin-lattice relaxation of polarised radi... more ABSTRACT Self-diffusion in solid Li was studied via the spin-lattice relaxation of polarised radioactive 8Li nuclei using their asymmetric beta -decay radiation. The diffusion-induced spin-lattice relaxation rate 1/T1diff was measured as a function of temperature from the melting point Tm=454K down to about 1/2Tm and as a function of the magnetic field from 8 to 700 mT. 1/T1diff can be explained assuming the nuclear dipole-dipole interaction alone. The data are analysed in the frame of the encounter model of correlated self-diffusion. The macroscopic self-diffusion coefficient DSD is determined over almost seven decades. A deviation from Arrhenius behaviour at elevated temperatures is interpreted in terms of a combined monovacancy/divacancy (1V/2V) mechanism. The correlation factor obtained from DSD and tracer self-diffusion coefficients DT, measured by mass spectroscopy, has a temperature dependence which is consistent with the 1V/2V model. The question of the possible existence of a non-classical isotope effect cannot be settled by a comparison of the present DSD values with those known from conventional nuclear magnetic resonance on 7Li.
Nuclear magnetic resonance measurements were carried out on neutron activated 20F(T1/2=11s) nucle... more Nuclear magnetic resonance measurements were carried out on neutron activated 20F(T1/2=11s) nuclei in a single crystal of KZnF3. The quadrupolar splitted NMR spectrum, detected via the 20F β-radiation asymmetry, could be observed using a radio frequency modulation technique. The quadrupole coupling constant was determined to e2 q Q/h= + (12.0 ± 1.5) MHz at room temperature. The sign of e2 q Q was obtained from a simultaneous γ-ray anisotropy measurement on the succeeding 20Ne transition. Utilising a calculated field gradient of the fluorine atom, an fQ = 4.6% is determined. This value is compared with literature data of similar compounds.
Solid state physics experiments were conducted on systems belonging to different substance classe... more Solid state physics experiments were conducted on systems belonging to different substance classes. Polarized radioactive probe nuclei were obtained in sample material by activation with spin-polarized thermal reactor neutrons. The decay radiation allows for the determination of nuclear resonance signals as well as die-away curves of the nucleus polarization by spin-lattice relaxation processes. The method was applied to ionic crystals, semiconductors, glasses, and metal melts. Dynamics and structure of intrinsics, radiation and doping effects, self diffusion and electronic properties are determined.
Owing to the structural flexibility of spinels, providing a wide range of physical and chemical b... more Owing to the structural flexibility of spinels, providing a wide range of physical and chemical behavior, these materials have been considered as a convenient model system for the investigation of the size dependent properties of complex ionic systems. In this work, quantitative information is obtained on the crystallite size dependent ionic configuration in nanosized spinel oxides prepared by mechanochemical processing of the corresponding bulk materials. Experimentally determined values of the crystallite size and of the mean degree of inversion of nanostructured spinels are used to calculate the volume fraction of interfaces/surfaces and their thickness in the nanomaterials.
TiO2 photocatalysts with predetermined phase composition (anatase-to-rutile ratio) have been prep... more TiO2 photocatalysts with predetermined phase composition (anatase-to-rutile ratio) have been prepared from strongly acidic aqueous HCl/TiCl4 mixtures with 0.1M≤[HCl]TOT≤5M and 0.05M≤[TiCl4]TOT≤3M (where the subscript TOT denotes total or analytical concentration). During the syntheses, TiCl4 was added to a cold-HCl solution. The initially precipitate free reaction mixture was boiled, resulting in the formation of large amount of solid, nanocrystalline (particle size
Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its a... more Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its application as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Nevertheless, diffusion in Li3N was studied by many groups and various techniques (see [1-3] and references therein) which predestines it to act as a model system for the establishment of new techniques. Li3N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li2N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li2N layer and Li(1) in the Li layer. Li diffusion in the Li2N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the caxis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions ca...
Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its a... more Lithium nitride, Li3N, is one of the best Li conductors at room temperature. Unfortunately, its application as electrolyte in batteries is limited due to the low decomposition potential of only 0.45 V. Nevertheless, diffusion in Li3N was studied by many groups and various techniques (see [1-3] and references therein) which predestines it to act as a model system for the establishment of new techniques. Li3N crystallizes in a layered structure of the hexagonal space group P6/mmm [3,4] (see Fig. 1). There are two alternating types of layers, one with the stoichiometry Li2N, the other containing only Li. As a result, there are two different Li positions, Li(2) in the Li2N layer and Li(1) in the Li layer. Li diffusion in the Li2N layer (ab-plane, intralayer diffusion) is fast, while the Li diffusion parallel to the caxis is moderate. The mechanism of this interlayer diffusion process is directly associated with a Li exchange between the two Li positions (see Fig. 1) since the Li ions ca...
Sustainable energy storage in the form of secondary Li ion batteries requires both the preparatio... more Sustainable energy storage in the form of secondary Li ion batteries requires both the preparation of advanced materials as well as the development of techniques being capable to characterize the transport properties of ionic conductors preferably on large time and length scales. By combining the various techniques of nuclear magnetic resonance (NMR) [1], which, in particular, include the generation and analysis of stimulated echoes, Li jump rates with values ranging from a few jumps per second up to rates of the order of some millions of jumps per millisecond can be studied [2-4]. In Fig. 1 an overview of the time windows accessible by various NMR techniques is given [2-4].
Sustainable energy storage in the form of secondary Li ion batteries requires both the preparatio... more Sustainable energy storage in the form of secondary Li ion batteries requires both the preparation of advanced materials as well as the development of techniques being capable to characterize the transport properties of ionic conductors preferably on large time and length scales. By combining the various techniques of nuclear magnetic resonance (NMR) [1], which, in particular, include the generation and analysis of stimulated echoes, Li jump rates with values ranging from a few jumps per second up to rates of the order of some millions of jumps per millisecond can be studied [2-4]. In Fig. 1 an overview of the time windows accessible by various NMR techniques is given [2-4].
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
In order to improve our understanding of the transport mechanisms of lithium in glasses, we have ... more In order to improve our understanding of the transport mechanisms of lithium in glasses, we have performed diffusion and ionic conductivity studies on spodumene composition (LiAlSi 2 O 6) glasses. In diffusion couple experiments pairs of chemically identical glasses with different lithium isotopy (natural Li vs pure 7 Li) were processed at temperatures between 482 and 732 K. Profiles of lithium isotopes were measured after the diffusion runs innovatively applying femtosecond UV laser ablation combined with inductively coupled plasma mass spectrometry (LA ICP-MS). Self-diffusion coefficients of lithium in the glasses were determined by fitting the isotope profiles. During some of the diffusion experiments the electrical conductivity of the samples was intermittently measured by impedance spectrometry. Combining ionic conductivity and self-diffusivity yields a temperature-independent correlation factor of ∼0.50, indicating that motions of Li ions are strongly correlated in this type of glasses. Lithium self-diffusivity in LiAlSi 2 O 6 glass was found to be very similar to that in lithium silicate glasses although Raman spectroscopy demonstrates structural differences between these glasses; that is, the aluminosilicate is completely polymerized while the lithium silicate glasses contain large fractions of nonbridging oxygen.
A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the ... more A sol-gel route for ternary lithium fluorides of transition metals (M) is presented allowing the synthesis of Li 3 MF 6-type and Li 2 MF 5-type compounds. It is based on a fluorolytic process using transition metal acetylacetonates as precursors. The domain size of the obtained powders can be controlled by modifying the conditions of synthesis. 6 Li and 7 Li magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy is used to study local environments of the Li ions in orthorhombic and monoclinic Li 3 VF 6 as well as Li 2 MnF 5. The number of magnetically inequivalent Li sites found by MAS NMR is in agreement with the respective crystal structure of the compounds studied. Quantum chemical calculations show that all materials have high de-lithiation energies making them suitable candidates to be used as high-voltage battery cathode materials.
Within the system Li2O – TiO2, lithium hexatitanate Li2Ti6O13 (i.e. Li2O ∙ 6 TiO2) was already st... more Within the system Li2O – TiO2, lithium hexatitanate Li2Ti6O13 (i.e. Li2O ∙ 6 TiO2) was already studied before by electrochemical methods with respect to its application as a potential Li-ion battery anode material [1, 2]. This compound is also attractive for fundamental cation diffusion studies, in particular due to its channel structure and the fact that Li and Na are interchangeable. The present work examines the effect of different Li : Na ratios in LixNa2-xTi6O13 on diffusion using impedance spectroscopy which measures the conductivity over a wide frequency range and thus on different length scales. This also enables the comparison with NMR results obtained by us in a separate study. Additionally, the Hebb-Wagner polarization (DC polarization) method is being used here to discriminate between the cation and a partial electronic conductivity [3].
Pulsed field gradient (PFG) NMR is applied to measure self-diffusion coefficients of 1,3,5 triiso... more Pulsed field gradient (PFG) NMR is applied to measure self-diffusion coefficients of 1,3,5 triisopropyl-benzene in the particles of several industrial FCC catalysts having different systems of mesoand macropores. Relating these diffusivities to the self-diffusion coefficient of 1,3,5 tri-isopropyl-benzene in the liquid phase, the tortuosity factors for diffusion in the mesoand macropores of the particles were obtained. The values of the tortuosity factors were found to increase with a increasing volumetric fraction of the small (< 20 nm) mesoand macropores in the total intraparticle volume.
Dedicated to Professor Werner MüllerWarmuth on the occasion of his 65th birthday Investigations o... more Dedicated to Professor Werner MüllerWarmuth on the occasion of his 65th birthday Investigations of Li diffusion in stage-1 and stage-2 Li graphite intercalation compounds with neutron time-of-flight and backscattering techniques and ^-radiation detected nuclear magnetic resonance/relaxation (/J-NMR) with the nucleus 8Li(T1/2 = 0.8 s) are reviewed and compared. De pending on temperature, the spin-lattice relaxation-rate T{1 of 8Li is governed by different pro cesses. Above 300 K, Tf1 (T) shows maxima induced by long-range Li+ diffusion. Jump correlation times are estimated. Inspection of the B field dependence of T f1 revealed two-dimensional diffusion behaviour. The neutron spectra showed a quasielastic line broadening above 500 K, which was used to obtain diffusion coefficients and to trace jump vectors of the in-plane motion. The diffusion parameters observed with both techniques are compared, and differences that show up are dis cussed. In addition, the low-temperature spin-la...
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