L. Pardi

INO - Istituto Nazionale di Ottica, Florens, Tuscany, Italy

Are you L. Pardi?

Claim your profile

Publications (160)489.58 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: A study is undertaken to ascertain whether changes in the speciation of inorganic radicals are occurring during the ceramic industrial production that involves abundant silica powders as raw material. Industrial dusts were sampled in two ceramic firms, immediately after the wet mixing stage, performed with the aid of a relevant pressure. The dusts were then characterised by means of X-ray diffraction, analysis of the trace elements through chemical methods, granulometry, continuous-wave electron paramagnetic resonance (EPR) and pulsed electron spin echo envelope modulation (ESEEM) spectroscopies. The results of the characterisation point to a relevant change in the speciation of the two samples; namely, a prevailing contribution due to an inorganic radical different from that pertaining to pure quartz is pointed out. The combined interpretation of EPR and ESEEM data suggests the attribution of the main paramagnetic contribution to the A-centre in kaolinite, a constituent that is added to pure quartz at the initial stage of the ceramic production. In one of the two samples, a second weak EPR signal is attributed to the quartz’s hAl species. By taking into account the relative quantities of quartz and kaolinite mixed in the two samples, and the relative abundances of the two radical species, we propose that the partial or complete suppression of the hAl species in favour of the A-centre of kaolinite has occurred. Although this change is apparently fostered by the mixture between quartz and another radical-bearing raw material, kaolinite, the suppression of the hAl centre of quartz is ascribed to the role played by the pressure and the wet environment during the industrial mixing procedure. This suppression provides a net change of radical speciation associated with quartz, when this phase is in contact with workers’ respiratory system.
    Physics and Chemistry of Minerals 12/2014; 42(5). DOI:10.1007/s00269-014-0726-5 · 1.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reorientation of TEMPO spin probe in semicrystalline poly(dimethylsiloxane) (PDMS) is investigated in the temperature range from the glassy region (below 147 K) up to the melt (above about 230 K) by high-field electron paramagnetic resonance (HF-EPR) spectroscopy at two different Larmor frequencies (190 and 285 GHz). The spin probe is confined in the disordered phase. Accurate numerical simulations evidence that the spin probe undergoes activated jump reorientation overcoming an exponential distribution of barrier heights characteristic of highly constrained systems and resulting in a power-law distribution of the reorientation times. Below 180 K the spin probe is coupled to local relaxations and does not sense the glass transition. A strong narrowing of the distribution of the reorientation times and a sudden drop of the mean value are observed at similar or equal to 213 K, above the onset of the melting at similar or equal to 209 K. Strikingly, it is found that the faster fraction of the spin probes does not sense the melting and couples to the segmental motion of the bulk amorphous PDMS from about 200 K onward. Our findings support the conclusion that the faster and the slower TEMPO molecules are located in (or very close to) the mobile (MAP) and the rigid (RAF) amorphous fractions of PDMS, respectively. The results suggest that MAP is negligible close to the glass transition but it is present above about 200 K, whereas RAF at about 211 K is reduced to about 896 and softens above 213 K, well below the melting transition (similar or equal to 230 K). Similarities between the disordered phase of semicrystalline PDMS and the PDMS layers in poly(styrene) PDMS diblock are discussed.
    Macromolecules 10/2014; 47(19):6748-6756. DOI:10.1021/ma501565z · 5.80 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The reorientation of a small paramagnetic tracer in poly(dimethylsiloxane) (PDMS) has been investigated by high-field electron paramagnetic resonance spectroscopy at a Larmor frequency of 285 GHz. The tracer is confined in the disordered phase of the semicrystalline PDMS. A sudden change of the rotational dynamics is observed close to the melting point (213 K) of the crystallites. This points to strong coupling between the crystalline and the disordered fractions of PDMS. Below the glass transition ( \(T_\mathrm{g} \sim 150 \mathrm{K}\) ), the tracer reorientation occurs via small angle jumps, with no apparent distribution of the correlation times. Above \(T_\mathrm{g}\) , a power-law distribution of correlation times is evidenced.
    Applied Magnetic Resonance 07/2014; 45(7):693-706. DOI:10.1007/s00723-014-0547-1 · 1.17 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We investigated the speciation of Fe in bulk and in suspended respirable quartz dusts coming from ceramic and iron-casting industrial processes via X-ray absorption spectroscopy, with the aim of contributing to a better understanding of the variability of crystalline silica toxicity. Four different bulk industrial quartz powders, nominally pure quartz samples with Fe contents below 200 ppm, and three respirable dusts filters were selected. Fe speciation was determined in all samples through a coupled study of the X-ray absorption near-edge structure and extended X-ray absorption fine structure regions, operating at the Fe-K edge. Fe speciation revealed common features at the beginning of the different production processes, whereas significant differences were observed on both respirable dusts and bulk dusts exiting from the production process. Namely, a common pollution of the raw quartz dusts by elemental Fe was evidenced and attributed to residuals of the industrial production of quartz materials. Moreover, the respirable samples indicated that reactivity occurs after the suspension of the powders in air. The gravitational selection during the particle suspension consistently allowed us to clearly discriminate between suspended and bulk dusts. On the basis of the obtained results, we provide an apparent spectroscopic discrimination between the raw materials used in the considered industrial processes, and those that are effectively inhaled by workers. In particular, an amorphous FeIII oxide, with an unsaturated coordination sphere, can be related to silica reactivity (and health consequences).
    Physics and Chemistry of Minerals 11/2013; 41(3). DOI:10.1007/s00269-013-0640-2 · 1.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: X-ray absorption spectroscopy investigation has been carried out at the Cu K edge on synthetic materials belonging to the ternary Cu-Sn-S system. In particular, Cu3SnS4 nanocrystalline powders, obtained through a solvothermal approach, and Cu4SnS4 microcrystalline powders, obtained through standard solid state reactions, were investigated.From the XANES spectra, Cu is confirmed to be monovalent in both samples, thus implying a complex mechanism to achieve charge balance in Cu3SnS4. In this sample, the Cu-S EXAFS distance is found surprisingly short, and this suggests that Cu ions could be shifted outside the barycentre of the tetrahedra. (© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 08/2013; 10(7‐8). DOI:10.1002/pssc.201200753
  • [Show abstract] [Hide abstract]
    ABSTRACT: High-field high-frequency Electron Paramagnetic Resonance spectroscopy (HF2-EPR) is a powerful tool to investigate, with ultra-high angular resolution, the rotational dynamics of complex systems like polymers, viscous fluids and glasses. Usually, information is drawn by detailed numerical analysis of the overall lineshape. Here, we present a simplified analytical model of the line shifts due to the rotational dynamics of the paramagnetic centre. The model captures the basic features of the reorientation process (time scale and size of the angular jump). It is compared with experimental results concerning the reorientation of a paramagnetic guest molecule dissolved in polystyrene. We find that, if the rotational model to describe the reorientation of the radical is consistent, the best-fit parameters yield equally acceptable best-fits of the overall spectrum by numerical simulations and dynamical line shifts by independent analytic expressions.
    Zeitschrift für Physikalische Chemie 12/2012; 226(11-12):1379-1394. DOI:10.1524/zpch.2012.0283 · 1.36 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The behaviour of a disc-shaped dielectric resonator (DR) working in the Whispering-Gallery Modes (WGM) when used for X-band ESR experiments has been tested. It has been verified that the WGM in the resonator can be excited by using the microwave bridge of a Bruker spectrometer. The microwave field is well confined in the DR also in the absence of metal shieldings as demonstrated by the high Q values of the detected resonances. A large number of such resonances has been detected from eight up to twelve gigahertz making the DR a very broadband device. ESR spectra of various powder and aqueous samples have been obtained and compared with those of the same samples recorded by using a metal cavity. The relative amplitude of the spectra demonstrated that for aqueous samples the sensitivity of DR is similar to that of the metallic cavity. Further investigations are in progress to enhance the overall performance.
    Applied Magnetic Resonance 10/2012; 3(5):827-840. DOI:10.1007/BF03260114 · 1.17 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Transition metal sulphides, grown in alternate layers by Electrochemical Atomic Layer Deposition (ECALD) to form thin films, are relevant candidates as photovoltaic materials for solar-cell production. However, the knowledge of the phase composition of the deposited sulphide, which is a fundamental information to assign and predict its effective semiconducting properties, is often hindered by the limited amount of material and by its morphological constraints. In the present study, an X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM) investigation of a copper sulphide thin film, synthesised according to the ECALD method, is proposed as an alternative and efficient way to identify the deposited semiconductor. The detailed XPS analysis of the Cu and S contents in the film points to a 1:1 stoichiometric ratio, corresponding to the CuS compound. Moreover, Cu is observed only as monovalent, and the possible co-existence of sulphide ions and of disulphide units is inferred. Accordingly, the attribution of the structure of the thin film to covellite, CuS, is proposed, as being the only one able to account for all experimental evidences. We suggest that the covellite structure can be set up by spontaneous rearrangement starting from a wurtzite-type CuS deposit, driven by the negative Gibbs energy involved in the formation of the compound from the elements. Finally the morphological characterisation of the film confirms its spatial homogeneity, thus making the covellite film a potential candidate for solar-cell applications.
    European Journal of Mineralogy 10/2012; 24(5):879-884. DOI:10.1127/0935-1221/2012/0024-2229 · 1.48 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The EPR spectrum of Mn 2+ in microcrystalline calcite geomaterials (e.g., marbles, travertinespossesses exceptional diagnostic characteristics, allowing to relate samples to their origin (natural/synthetic, inorganic, organogenic, ⋯and to evaluate the details of impurities clustering. This information, beyond their mineralogical and geochemical interest, is of paramount importance for environmental, palaeoclimatic, and cultural heritage studies. Accessing the information hidden in the Mn 2+ EPR spectrum relies on disentangling spurious self-correlation among spin Hamiltonian parameters in the powder spectrum. In the present study, this goal is achieved through a systematic comparison of the temperature dependencies of four different microcrystalline calcite geomaterials. Accordingly, an assessment of the internal correlation structure of the spin Hamiltonian parameters is provided and the most sensitive discriminating parameters, which are able to mark samples, are identified. It has been found that the spin Hamiltonian parameters useful for discrimination purposes are those which are dependent on the ligand field interaction, whereas the Fermi contact interaction, as well as the spin-spin, spin-phonon, and spin-lattice interactions, are not able to "store" information related to formation processes, nor post-depositional events. This characteristic behavior is ascribed to the occurrence of mosaic structure and to the clustering among Mn 2+ and other impurity ions, which are able to induce a strong and variable ligand field interaction. In particular, the proposed method appears fully able to reveal the biogenic origin of microcrystalline calcites and to trace post-depositional events.
    American Mineralogist 10/2012; 97(10):1619-1626. DOI:10.2138/am.2012.4168 · 1.96 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A set of raw industrial materials, that is, pure quartz and quartz-rich mixtures, were investigated through electron paramagnetic resonance and electron spin echo-envelope modulation spectroscopies, with the aim of evaluating the effective role played by defect centres and of assessing whether they can be used to monitor changes in the physical properties of quartz powders with reference to their health effects. The obtained results point to two interactions of the Al defect centres with H+, hosted in sites within the channels parallel and perpendicular to the c axis of quartz, respectively. These two Al/H+ (hAl) centres exhibit a weak chemical bond, and their relative amounts appear to be modified/controlled by the thermo-mechanical processes underwent by powders. Indeed, a mechanically promoted inter-conversion between the two kinds of site is suggested. As a consequence, the hAl centres are effective in monitoring even modest activations of powders, through thermal or mechanical processes, and they are also supposed to play a specific, relevant role in quartz reactivity during the considered industrial processes.
    Physics and Chemistry of Minerals 06/2012; 39(6). DOI:10.1007/s00269-012-0502-3 · 1.54 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: At frequencies above 150 GHz conventional microwave techniques become unsuitable for electron magnetic resonance (EMR) spectroscopy applications. Quasi-optical techniques are the general frame into which the different approaches to high-field high-frequency EMR (HF2-EMR) have been developed. Beyond the single-pass approach the existing HF2-EMR spectrometers make use of Fabry-Perot resonators. In this paper the use of an alternative resonating structure on the basis of the use of whispering gallery mode dielectric resonators is shown. The physics of these resonators and their implementation in a HF2-EMR probe head are described. Their use in HF2-EMR experiments performed on standard samples is described and the results of these experiments critically discussed in order to have insight into the open problems of the employed spectrometer; the more promising solutions to these problems, actually under development, are briefly outlined.
    Applied Magnetic Resonance 04/2012; 19(3):495-506. DOI:10.1007/BF03162393 · 1.17 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We have applied pulsed laser deposition (PLD) to fabricate YBCO/YSZ films (short length) onto biaxially textured NiFe substrates. Macroscopic characterization of the samples has been carried out by electrical measurements, XRD patterns and pole figures. Our best films are characterized by Tcs around 89 K and transition widths around 5–6 K. Bragg–Brentano spectra and pole figures acquired on the {111} peak for YSZ and {013} for YBCO show the achievement of the correct crystalline structure and stoichiometry both in YSZ and in YBCO layers. They are largely in-plane textured (respectively (001) <110> for YSZ and (001) <100> for YBCO), and the superconducting YBCO layer exhibits a relatively low mosaicity. Atomic-force microscopy (AFM) analysis confirmed the presence of large grains (1–2 μm typical dimensions), and the occurrence of a complex morphology in the YBCO layer.
    International Journal of Modern Physics B 01/2012; 17(04n06). DOI:10.1142/S0217979203016546 · 0.94 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A multidisciplinary characterization of an active thermal spring in central Italy has been undertaken with the aim of (i) ascertaining whether microbiological activity plays a relevant role in hot-depositing travertines and (ii) establishing an experimental protocol able to identify similar effects in fossil travertines. Water, gas, and travertine samples were investigated by chemical (ICP/MS, SEM/EDS), physical (DTA–DTG), isotopic (δ18O, δD, and δ13C), mineralogical (XRPD), and spectroscopic (EPR) techniques. Twenty-four samples (three for each phase) were collected every 5°C temperature drop, along a ∼100m long artificial channel near Viterbo (Bullicame 3, Latium, central Italy). A microbiological characterization was carried out in parallel, sampling the channel every 10°C temperature drop.The Bullicame 3 system is revealed to be composed of two markedly different subsystems: a water/gas interface, where a kinetically fast exchange allows equilibrium of components both in water and in gases; a solid/water interface, where travertine precipitation occurs, influenced by microbiological activity. A peculiar lattice shrinking of calcite was identified, as well as an anomalous value of the zero-field splitting parameter from the EPR measurements. The interpretation of these anomalies is confirmed by the identification of calcifying cyanobacteria throughout the channel path.Our results point out that microbiological activity can play a significant role in travertine deposition from hot springs. Furthermore, the proposed approach, representing a tool to identify crystal chemical remnants of past microbiological activity, could be applicable to fossil travertines.
    Geochimica et Cosmochimica Acta 08/2011; 75(16):4441-4455. DOI:10.1016/j.gca.2011.05.011 · 4.33 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An extensive characterisation of the magnetic properties of synthetic powders of kuramite, with formal composition Cu3SnS4, was performed. Powders were investigated through superconducting quantum interference device (SQUID) magnetometry, electron paramagnetic resonance (EPR) spectroscopy, X-ray powder diffraction (XRPD), scanning and transmission electron microscopies (SEM and TEM) and microanalysis. SEM and TEM reveal the presence of nanodimensioned particles. XRPD clearly shows that Cu3SnS4 crystallised in a cubic sphalerite-type structural model, in spite of the stannite-type tetragonal structure described for the natural phase. This difference arises from a full random distribution of cations. Synthetic kuramite nanopowders exhibit a marked paramagnetism, originated by the presence of Cu(II), definitely assessed by EPR measurements. Moreover, the overall magnetic behaviour of the sample cannot be simply ascribed to diluted paramagnetism, and this suggests the presence of strong superexchange interactions among Cu(II) ions even at room temperature. The main consequences of these results are the definitive assessment of the chemical formula Cu(I)2Cu(II)SnS4 and of a random distribution of Cu(II), Cu(I) and Sn(IV) ions within the available tetrahedral sites.
    Physics and Chemistry of Minerals 06/2011; 38(6):483-490. DOI:10.1007/s00269-011-0421-8 · 1.54 Impact Factor
  • ChemInform 12/2010; 29(48). DOI:10.1002/chin.199848347
    [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 09/2010; 26(37). DOI:10.1002/chin.199537285
  • D. Gatteschi · L. Pardi
    ChemInform 03/2010; 25(10):no-no. DOI:10.1002/chin.199410319
  • [Show abstract] [Hide abstract]
    ABSTRACT: A multifrequency Electron Paramagnetic Resonance (EPR) investigation of Ce3+ impurities in PbWO4 single-crystals at the conventional microwave frequency (CMF) (X-band: 9.43GHz) and at the high frequencies/fields (HF) 95, 190 and 285GHz was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective spin one-half system in a tetragonal site symmetry. The diagonal values of the effective g matrix of the lowest doublet of the ground multiplet, g‖ and g⊥, are frequency dependent at high fields. For the magnetic field perpendicular to the tetragonal axis, the g⊥-parameter exhibits also a small azimuthal angular dependence, which is frequency dependent, corresponding to the tetragonal S4 symmetry. These HF effects are associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. The CMF and multifrequency HF-EPR analysis gives a good description of the magnetic properties and allows an estimation of the crystal field splitting of the ground multiplet of Ce3+ ions with tetragonal symmetry S4 in the PbWO4 scintillator.
    Optical Materials 03/2010; 32(5):570-575. DOI:10.1016/j.optmat.2009.11.015 · 1.98 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A multifrequency electron paramagnetic resonance (EPR) investigation of Nd(3+) impurities in PbWO(4) single-crystals at the conventional microwave frequency (MF) 9.43 GHz, and at the 95, 190, and 285 GHz high frequencies was carried out. The resulting spectra are well described at all frequencies by an axial spin-Hamiltonian corresponding to an effective electron spin of one-half and to a tetragonal symmetry. For the magnetic field along the tetragonal axis, the g(parallel)-factor and the hyperfine constant A(parallel) of the lowest doublet of the ground multiplet decreases with frequency increase. For the magnetic field perpendicular to the tetragonal axis, the g(perpendicular)-factor exhibits a small azimuthal angular dependence that increases with increasing the frequency due to the S(4) site symmetry. The azimuthal angular dependence allows to clearly distinguish between different local axial symmetries. These properties are interpreted as high field/frequency (HF) effects associated with the mixing by the large Zeeman interaction of some of the upper-lying doublets of the ground multiplet into the lowest-lying doublet states. We show that from the combined analysis of the multifrequency MF- and HF-EPR spectra and of the optical data, an accurate description of the ground multiplet of the Kramers rare earth ions in solid matrices can be derived.
    The Journal of Chemical Physics 08/2009; 131(3):034505. DOI:10.1063/1.3180697 · 2.95 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: An X-ray absorption spectroscopy (XAS) study of the Fe local environment in natural amethyst (a variety of α-quartz, SiO2) has been carried out. Room temperature measurements were performed at the Fe K-edge (7,112eV), at both the X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) regions. Experimental results were then compared with DFT calculations. XANES experimental spectra suggest Fe to occur mainly in the trivalent state, although a fraction of Fe2+ is identified. EXAFS spectra, on the other hand, reveal an unusual short distance for the first coordination shell: <Fe–O>=1.78(2)Å, the coordination number being 2.7(5). These results allow to establish that Fe replaces Si in its tetrahedral site, and that numerous local distortions are occurring as a consequence of the presence of Fe3+ variably compensated by protons and/or alkaline ions, or uncompensated. The formal valence of Fe, on the basis of both experimental and DFT structural features, can be either 4+ or 3+. Taking into account the XANES evidences, we suggest that Fe mainly occurs in the trivalent state, compensated by protons, and that a minor fraction of Fe4+ is stabilised by the favourable local structural arrangement. KeywordsAmethyst-Fe-XANES-EXAFS-DFT calculations-Fe bioavailability
    Physics and Chemistry of Minerals 05/2009; 37(5):283-289. DOI:10.1007/s00269-009-0332-0 · 1.54 Impact Factor

Publication Stats

4k Citations
489.58 Total Impact Points


  • 2008–2014
    • INO - Istituto Nazionale di Ottica
      Florens, Tuscany, Italy
  • 1988–2013
    • University of Florence
      • Dipartimento di Chimica "Ugo Schiff"
      Florens, Tuscany, Italy
    • Università degli Studi di Perugia
      Perugia, Umbria, Italy
  • 1984–2012
    • Università di Pisa
      • • Department of Physics "E.Fermi"
      • • Department of Information Engineering
      Pisa, Tuscany, Italy
  • 1975–2011
    • National Research Council
      • Institute of Chemistry of Organometallic Compounds ICCOM
      Roma, Latium, Italy
  • 1997–2002
    • Florida State University
      • Department of Chemistry and Biochemistry
      Tallahassee, Florida, United States
  • 1998–2000
    • Roosevelt University
      • Department of Biological, Chemical and Physical Sciences
      Chicago, Illinois, United States
  • 1999
    • Indiana University Bloomington
      • Department of Chemistry
      Bloomington, Indiana, United States
  • 1997–1998
    • National High Magnetic Field Laboratory
      Tallahassee, Florida, United States
  • 1986
    • Università degli studi di Parma
      Parma, Emilia-Romagna, Italy