Marcello Mazzani | Università degli Studi di Parma (Italy) (original) (raw)
Papers by Marcello Mazzani
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetal... more The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetallic [Co 8 Pt 4 C 2 (CO) 24 ] 2-, [1] 2-, carbonyl cluster.
Physical Review B, 2007
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e − ) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
Europhysics Letters (epl), 2011
Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based supercon... more Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based superconductors PACS 74.25.nj -Nuclear magnetic resonance
Physica Status Solidi B-basic Solid State Physics, 2008
The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated... more The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated ampoules, has been studied by monitoring the evolution of the Raman spectra. Reduction of some Raman bands associated with “in-plane” structural defects, such as vacancies, dislocations or grain boundaries, and those associated with “out-of-plane” defects, such as stacking faults, is accompanied by the rise of new bands around 1180 and 2000 cm–1. The development of these bands is suppressed in nanographite samples exposed to a flux of pure anhydrous hydrogen. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physical Review B, 2011
We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) study of nanosized graphite particles prepared by ball milling. In as-prepared samples a very intense and sharp EPR resonance at g=2.0035 has been measured. The EPR line width shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere, changes in the EPR signal suggest gradual structural reconstruction where the localized edge states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈23K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) study of nano-sized graphite particles prepared by ball-milling. In as-prepared samples a very intense and sharp EPR resonance at g = 2.0035 has been measured. The EPR linewidth shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere changes in the EPR signal suggest gradual structural reconstruction where the localized edge-states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈ 23 K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
Physical Review Letters, 2009
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
![Research paper thumbnail of Magnetic Behavior of Odd and Even-Electron Metal Carbonyl Clusters: The Case Study of [Co 8 Pt 4 C 2 (CO) 24 ] n − ( n = 1, 2) Carbide Cluster](https://attachments.academia-assets.com/49894467/thumbnails/1.jpg)
](Journal of The American Chemical Society, 2010
The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetal... more The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetallic [Co 8 Pt 4 C 2 (CO) 24 ] 2-, [1] 2-, carbonyl cluster.
New Journal of Physics, 2008
In this report we combine synchrotron powder X-ray diffraction, 7 Li nuclear magnetic resonance (... more In this report we combine synchrotron powder X-ray diffraction, 7 Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li 4 C 60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR however reveals the presence of intrinsic centers originating from broken C 60 -C 60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7 Li NMR shift. Li + ions are at low temperatures on the 7 Li NMR timescale statically disordered. The observed 7 Li NMR line narrowing T > 200 K is ascribed to the Li + diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results in the gradual depolymerisation to the metallic monomer fcc high temperature structure. The transformation is first order and polymer as well as monomer phases coexist over broad temperature interval (130 K).
Physical Review B, 2007
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e − ) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
Europhysics Letters (epl), 2011
Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based supercon... more Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based superconductors PACS 74.25.nj -Nuclear magnetic resonance
Physical Review Letters, 2010
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Physica Status Solidi B-basic Solid State Physics, 2008
The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated... more The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated ampoules, has been studied by monitoring the evolution of the Raman spectra. Reduction of some Raman bands associated with “in-plane” structural defects, such as vacancies, dislocations or grain boundaries, and those associated with “out-of-plane” defects, such as stacking faults, is accompanied by the rise of new bands around 1180 and 2000 cm–1. The development of these bands is suppressed in nanographite samples exposed to a flux of pure anhydrous hydrogen. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of The American Chemical Society, 2010
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
Physical Review Letters, 2010
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Journal of The American Chemical Society, 2010
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
Physical Review B, 2011
We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) study of nanosized graphite particles prepared by ball milling. In as-prepared samples a very intense and sharp EPR resonance at g=2.0035 has been measured. The EPR line width shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere, changes in the EPR signal suggest gradual structural reconstruction where the localized edge states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈23K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) study of nano-sized graphite particles prepared by ball-milling. In as-prepared samples a very intense and sharp EPR resonance at g = 2.0035 has been measured. The EPR linewidth shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere changes in the EPR signal suggest gradual structural reconstruction where the localized edge-states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈ 23 K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
Physical Review Letters, 2009
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetal... more The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetallic [Co 8 Pt 4 C 2 (CO) 24 ] 2-, [1] 2-, carbonyl cluster.
Physical Review B, 2007
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e − ) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
Europhysics Letters (epl), 2011
Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based supercon... more Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based superconductors PACS 74.25.nj -Nuclear magnetic resonance
Physica Status Solidi B-basic Solid State Physics, 2008
The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated... more The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated ampoules, has been studied by monitoring the evolution of the Raman spectra. Reduction of some Raman bands associated with “in-plane” structural defects, such as vacancies, dislocations or grain boundaries, and those associated with “out-of-plane” defects, such as stacking faults, is accompanied by the rise of new bands around 1180 and 2000 cm–1. The development of these bands is suppressed in nanographite samples exposed to a flux of pure anhydrous hydrogen. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Physical Review B, 2011
We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) study of nanosized graphite particles prepared by ball milling. In as-prepared samples a very intense and sharp EPR resonance at g=2.0035 has been measured. The EPR line width shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere, changes in the EPR signal suggest gradual structural reconstruction where the localized edge states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈23K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) study of nano-sized graphite particles prepared by ball-milling. In as-prepared samples a very intense and sharp EPR resonance at g = 2.0035 has been measured. The EPR linewidth shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere changes in the EPR signal suggest gradual structural reconstruction where the localized edge-states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈ 23 K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
Physical Review Letters, 2009
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
Journal of The American Chemical Society, 2010
The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetal... more The reaction of [Co 6 C(CO) 15 ] 2with 2 equiv of PtCl 2 (Et 2 S) 2 affords the new heterobimetallic [Co 8 Pt 4 C 2 (CO) 24 ] 2-, [1] 2-, carbonyl cluster.
New Journal of Physics, 2008
In this report we combine synchrotron powder X-ray diffraction, 7 Li nuclear magnetic resonance (... more In this report we combine synchrotron powder X-ray diffraction, 7 Li nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR) experiments to study the structural evolution of Li 4 C 60 and how its electronic ground state depends on the crystal symmetry. The compound in the two-dimensional polymer phase with mixed interfullerene bonding motifs is a band gap insulator. EPR however reveals the presence of intrinsic centers originating from broken C 60 -C 60 bonds and local Li off-stoichiometry that create states in the band gap and account for the complex temperature dependence of the spin susceptibility as well as the residual temperature dependence of the 7 Li NMR shift. Li + ions are at low temperatures on the 7 Li NMR timescale statically disordered. The observed 7 Li NMR line narrowing T > 200 K is ascribed to the Li + diffusion dynamics and above room temperature the polymer phase is already a good ionic conductor. Heating the sample to temperatures above ∼470 K results in the gradual depolymerisation to the metallic monomer fcc high temperature structure. The transformation is first order and polymer as well as monomer phases coexist over broad temperature interval (130 K).
Physical Review B, 2007
The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remark... more The restoration of metallicity in the high-temperature, cubic phase of Li4C60 represents a remarkable feature for a member of the A4C60 family (A = alkali metal), invariably found to be insulators. Structural and resonance technique investigations on Li4C60 at T ¿ 600 K, show that its fcc structure is associated with a complete (4e − ) charge transfer to C60 and a sparsely populated Fermi level. These findings not only emphasize the crucial role played by lattice symmetry in fulleride transport properties, but also re-dimension the role of Jahn-Teller effects in band structure determination.
Europhysics Letters (epl), 2011
Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based supercon... more Metal-insulator transitions and other electronic transitions PACS 74.70.Wz -Carbon-based superconductors PACS 74.25.nj -Nuclear magnetic resonance
Physical Review Letters, 2010
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Physica Status Solidi B-basic Solid State Physics, 2008
The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated... more The structural relaxation of nanographite ball-milled in argon atmosphere and stored in evacuated ampoules, has been studied by monitoring the evolution of the Raman spectra. Reduction of some Raman bands associated with “in-plane” structural defects, such as vacancies, dislocations or grain boundaries, and those associated with “out-of-plane” defects, such as stacking faults, is accompanied by the rise of new bands around 1180 and 2000 cm–1. The development of these bands is suppressed in nanographite samples exposed to a flux of pure anhydrous hydrogen. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Journal of The American Chemical Society, 2010
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
Physical Review Letters, 2010
We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its... more We report an NMR and magnetometry study on the expanded intercalated fulleride Cs3C60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures pc and temperatures Tc. Though the ground state magnetism of the Mott phases differs, their high T paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.
Journal of The American Chemical Society, 2010
We report here on the preparation and characterization of a fullerenium salt in the solid state, ... more We report here on the preparation and characterization of a fullerenium salt in the solid state, where the fullerene is in the 2+ oxidized state. To succeed in this long-standing challenge, we exploit the oxidizing power of one of the strongest Lewis acids, AsF 5 . The weak nucleophilic character of its conjugate base is essential in stabilizing the fullerene dication in a crystal lattice. High-resolution structural analysis of this compound, with the formula C 60 (AsF 6 ) 2 , indicates that the highly reactive C 60 2+ units are arranged according to a novel 1D "zigzag" polymer structure. The molecules are connected by an alternating sequence of four-membered carbon rings ([2 + 2] cycloaddition) and single C-C bonds. The long awaited high-T c superconductivity and magnetism, expected in a hole-doped C 60 compound, are replaced instead by a semiconducting behavior, quite probably originating from the reduced crystal and molecular symmetry upon polymerization. The small value of the energy gap (approximately 70 meV) suggests, nevertheless, the proximity of a metallic phase.
Physical Review B, 2011
We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature-dependent x-band electron paramagnetic resonance (EPR) study of nanosized graphite particles prepared by ball milling. In as-prepared samples a very intense and sharp EPR resonance at g=2.0035 has been measured. The EPR line width shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere, changes in the EPR signal suggest gradual structural reconstruction where the localized edge states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈23K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) stud... more We report on a systematic temperature dependent X-band electron paramagnetic resonance (EPR) study of nano-sized graphite particles prepared by ball-milling. In as-prepared samples a very intense and sharp EPR resonance at g = 2.0035 has been measured. The EPR linewidth shows a Korringa-like linear temperature dependence arising due to the coexistence and strong exchange coupling of itinerant and localized edge states. With a prolonged aging in inert atmosphere changes in the EPR signal suggest gradual structural reconstruction where the localized edge-states dominate the EPR signal. In this case the EPR spin susceptibility shows a maximum at ≈ 23 K indicating the development of antiferromagnetic correlations as expected for the graphene lattice with a bipartite symmetry.
Physical Review Letters, 2009
We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a cry... more We report on the extraordinary superionic conductivity in the fulleride polymer Li 4 C 60 , a crystalline material with no disorder. 7 Li, NMR, and dc frequency dependent conductivity show uncorrelated ionic hopping across small energy barriers (ÁE a $ 200 meV) and an ionic conductivity of 10 À2 S=cm at room temperature, higher than in ''standard'' ionic conductors. Ab initio calculations of the molecular structure find intrinsic unoccupied interstitial sites that can be filled by Li þ cations in stoichiometric Li 4 C 60 even at low temperatures. The low energy required for the occupation of these sites allows a sizable Li þ diffusion above 130 K. The results suggest novel application of lithium intercalated fullerides as electrodes in Li ions batteries.
Macroscopic quantities of graphenes have been prepared by different chemical methods and characte... more Macroscopic quantities of graphenes have been prepared by different chemical methods and characterized by µSR spectroscopy, which proved a useful tool to study the interactions of the hydrogen atom with the defective graphene plane. A clear muon spin precession is observed in all the samples, contrary to the standard behaviour of graphite. Its origin lies in the magnetic dipolar interactions of hydrogen nuclei present at defects and reveal the formation of an extremely stable CHM u (CH 2 ) state. The signal amplitude suggests that vacancies saturated by hydrogen have an extraordinary hydrogen capture cross-section. In addition the µSR results, together with our SQUID investigations, pose important limits on the debated possibility of magnetism in graphene: µSR, indeed, is very sensitive to the local internal field and does not show the presence of any magnetization.
Il fullerene ei suoi derivati sono materiali molecolari di recente scoperta, che suscitano intere... more Il fullerene ei suoi derivati sono materiali molecolari di recente scoperta, che suscitano interesse nella comunita scientifica sia per l'affascinante varieta delle loro proprieta fisiche, che per le potenziali applicazioni tecnologiche.