Different amplitude and time distribution of the sound of light and classical music

Several pieces of different musical kinds were studied measuring $N(A)$, the output amplitude of a peak detector driven by the electric signal arriving to the loudspeaker. Fixed a suitable threshold $\bar{A}$, we considered $N(A)$, the number of times that $A(t)>\bar{A}$, each of them we named event and $N(t)$, the distribution of times $t$ between two consecutive events. Some $N(A)$ and $N(t)$ distributions are displayed in the reported logarithmic plots, showing that jazz, pop, rock and other popular rhythms have noise-distribution, while classical pieces of music are characterized by more complex statistics. We pointed out the extraordinary case of the aria ``\textit{La calunnia \`{e} un venticello}'', where the words describe an avalanche or seismic process, calumny, and the rossinian music shows $N(A)$ and $N(t)$ distribution typical of earthquakes.Comment: 3 pages with 4 figures, to be published in The European Physical Journal

Sintesi e caratterizzazione di ferriti nanostrutturate

In this thesis, the synthesis of transition and/or metal iron ferrite systems (both in the spinel MFe2O4 and perovskite MFeO3 form) through wet-chemistry synthetic routes was explored. Three specific routes were employed: i) nonaqueous sol-gel synthesis, ii) coprecipitation of oxalates from an aqueous solution and iii) hydrothermal synthesis coupled with oxalate coprecipitation. All three routes successfully allowed to synthesise iron ferrites (though the nature and characteristics of the prepared compounds varied depending on the chosen method). The spinel ferrites CoFe2O4, MgFe2O4, MnFe2O4, NiFe2O4 and ZnFe2O4, as well as the perovskites MnFeO3 and SrFeO3-δ were obtained as crystalline powders. All powders (except MgFe2O4) were obtained as pure, single-phase compounds. The obtained materials were then characterised through a wide array of techniques from the compositional, structural and functional points of view. In particular, bulk atomic ratios were investigated trough ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) and compared with surface composition explored through XPS (X-ray Photoelectron Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) and microanalysis allowed to study the evolution of the system during calcination and to evaluate the presence of residual organic moieties (from the synthesis precursors) in the materials. XRD (X-Ray Diffraction) and TPXRD (Temperature-Programmed XRD) were employed to investigate powder structure and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained was compared with micrographs collected through TEM (Transmission Electron Microscopy). In parallel, XPS, Mössbauer spectroscopy and TPR (Temperature Programmed Reduction) afforded information on the oxidation states and chemical environments of the elements in the material (both in bulk and on the surface). In the case of spinel ferrites, Mössbauer spectroscopy was particularly useful as it allowed to calculate the degree of inversion of the compounds. From a functional point of view, SQUID (Superconducting Quantum Interference Device) measurements were employed to study the magnetic properties of the materials, revealing that the cobalt and manganese spinels displayed ferrimagnetic behaviour (as expected), whereas the manganese perovskite was paramagnetic above 35 K (Néel temperature) and displayed ferrimagnetic behaviour below that temperature. Electric characterisations to gain insight on the conduction properties of the materials were carried out through BES (Broadband Electric Spectroscopy). These measurements revealed relaxations at 30 and 90°C in the cobalt and nickel spinels which are compatible with water intercalation within the crystal structure. As far as the manganese perovskite is concerned, the relaxations at 100°C and higher conductivity displayed compared to the spinels are compatible with ionic conduction. The catalytic activity was investigated through temperature-programmed oxidation of methane (CH4-TPO), showing that the synthesised cobalt, manganese, magnesium and nickel ferrites were active in the oxidation of methane to carbon dioxide, despite not being stable over several cycles. The effect of synthetic parameters (such as nature of the precursors, additives, thermal treatment parameters, aging time etc.) on the final structural and compositional nature of the oxides was the object of particular interest. Based upon the results obtained from these investigations, the synthetic protocols for each route were optimised in order to maximise product purity and yield, as well as to improve synthetic conditions; in particular, efforts were made to lower treatment temperatures and shorten treatment times whilst suffering no losses in terms of product yield and quality. In particular, hydrothermal syntheses of the nickel, cobalt, zinc and manganese spinels were successfully carried out at 75°C with a 4 hour treatment. In addition, the possible application of the coprecipitation of oxalates from an aqueous solution method to prepare iron ferrites containing two metals was explored: the Co0.5Mn0.5Fe2O4, Co0.5Mg0.5Fe2O4 and Co0.5Mn0.5FeO3 systems were successfully prepared and characterised. Measurement of bulk atomic ratios between the three metals in each mixed-metal ferrite (i.e. Co, Fe and either Mg or Mn) revealed that the chosen synthetic route afforded good control over the final stoichiometry of the prepared material

Low-temperature wet chemistry synthetic approaches towards ferrites

Ferrites are a broad class of iron-containing oxides that includes spinel ferrites MFe2O4, perovskites MFeO3, and hexagonal ferrites (hexaferrites) such as BaFe12O19. These materials have a wide array of applications owing to their diverse properties: notable instances include catalysis, piezoelectric components, magnetic components, biomedical applications, heterogeneous catalysis and photocatalysis. Given the growing importance of environmentally friendly, low-temperature methodologies to obtain functional materials, there is a growing interest in synthetic approaches which are compatible with the principles of “green chemistry”. In this context, wet chemistry represents an attractive choice, and furthermore offers the possibility of scale-up for manufacture of materials in volumes for practical application. Though there is a sizeable amount of literature on the synthesis of ferrites, the most common approaches require treatments at temperatures above 200 °C, either as the main synthetic procedure itself (thermal decomposition), or as a post-synthetic step (for example, calcination after sol–gel autocombustion). This review aims at summarising, categorising, classifying and critically discussing the different low-temperature (<200 °C), wet chemistry approaches employed in recent years for the synthesis of ferrites. This will include hydrothermal, solvothermal, sonochemical, and microwave methods, with examples taken from literature making reference to the various sub-classes of ferrites

Avalanches in Breakdown and Fracture Processes

We investigate the breakdown of disordered networks under the action of an increasing external---mechanical or electrical---force. We perform a mean-field analysis and estimate scaling exponents for the approach to the instability. By simulating two-dimensional models of electric breakdown and fracture we observe that the breakdown is preceded by avalanche events. The avalanches can be described by scaling laws, and the estimated values of the exponents are consistent with those found in mean-field theory. The breakdown point is characterized by a discontinuity in the macroscopic properties of the material, such as conductivity or elasticity, indicative of a first order transition. The scaling laws suggest an analogy with the behavior expected in spinodal nucleation.Comment: 15 pages, 12 figures, submitted to Phys. Rev. E, corrected typo in authors name, no changes to the pape

Sintesi e caratterizzazione di ferriti nanostrutturate

In this thesis, the synthesis of transition and/or metal iron ferrite systems (both in the spinel MFe2O4 and perovskite MFeO3 form) through wet-chemistry synthetic routes was explored. Three specific routes were employed: i) nonaqueous sol-gel synthesis, ii) coprecipitation of oxalates from an aqueous solution and iii) hydrothermal synthesis coupled with oxalate coprecipitation. All three routes successfully allowed to synthesise iron ferrites (though the nature and characteristics of the prepared compounds varied depending on the chosen method). The spinel ferrites CoFe2O4, MgFe2O4, MnFe2O4, NiFe2O4 and ZnFe2O4, as well as the perovskites MnFeO3 and SrFeO3-δ were obtained as crystalline powders. All powders (except MgFe2O4) were obtained as pure, single-phase compounds. The obtained materials were then characterised through a wide array of techniques from the compositional, structural and functional points of view. In particular, bulk atomic ratios were investigated trough ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) and compared with surface composition explored through XPS (X-ray Photoelectron Spectroscopy). TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) and microanalysis allowed to study the evolution of the system during calcination and to evaluate the presence of residual organic moieties (from the synthesis precursors) in the materials. XRD (X-Ray Diffraction) and TPXRD (Temperature-Programmed XRD) were employed to investigate powder structure and to calculate average crystallite sizes (through Rietveld refinement), and the data thus obtained was compared with micrographs collected through TEM (Transmission Electron Microscopy). In parallel, XPS, Mössbauer spectroscopy and TPR (Temperature Programmed Reduction) afforded information on the oxidation states and chemical environments of the elements in the material (both in bulk and on the surface). In the case of spinel ferrites, Mössbauer spectroscopy was particularly useful as it allowed to calculate the degree of inversion of the compounds. From a functional point of view, SQUID (Superconducting Quantum Interference Device) measurements were employed to study the magnetic properties of the materials, revealing that the cobalt and manganese spinels displayed ferrimagnetic behaviour (as expected), whereas the manganese perovskite was paramagnetic above 35 K (Néel temperature) and displayed ferrimagnetic behaviour below that temperature. Electric characterisations to gain insight on the conduction properties of the materials were carried out through BES (Broadband Electric Spectroscopy). These measurements revealed relaxations at 30 and 90°C in the cobalt and nickel spinels which are compatible with water intercalation within the crystal structure. As far as the manganese perovskite is concerned, the relaxations at 100°C and higher conductivity displayed compared to the spinels are compatible with ionic conduction. The catalytic activity was investigated through temperature-programmed oxidation of methane (CH4-TPO), showing that the synthesised cobalt, manganese, magnesium and nickel ferrites were active in the oxidation of methane to carbon dioxide, despite not being stable over several cycles. The effect of synthetic parameters (such as nature of the precursors, additives, thermal treatment parameters, aging time etc.) on the final structural and compositional nature of the oxides was the object of particular interest. Based upon the results obtained from these investigations, the synthetic protocols for each route were optimised in order to maximise product purity and yield, as well as to improve synthetic conditions; in particular, efforts were made to lower treatment temperatures and shorten treatment times whilst suffering no losses in terms of product yield and quality. In particular, hydrothermal syntheses of the nickel, cobalt, zinc and manganese spinels were successfully carried out at 75°C with a 4 hour treatment. In addition, the possible application of the coprecipitation of oxalates from an aqueous solution method to prepare iron ferrites containing two metals was explored: the Co0.5Mn0.5Fe2O4, Co0.5Mg0.5Fe2O4 and Co0.5Mn0.5FeO3 systems were successfully prepared and characterised. Measurement of bulk atomic ratios between the three metals in each mixed-metal ferrite (i.e. Co, Fe and either Mg or Mn) revealed that the chosen synthetic route afforded good control over the final stoichiometry of the prepared materialsIn questa tesi è stata esplorata la sintesi di sistemi di ferriti contenenti ferro e uno o più metalli di transizione o alcalino terrosi (sia in forma di spinello MFe2O4 che di perovskite MFeO3) tramite metodi di sintesi per via umida. Sono state impiegate tre specifiche metodologie di sintesi: i) sintesi sol-gel non acquosa ii) coprecipitazione di ossalati da una soluzione acquosa e iii) sintesi idrotermale accoppiata alla coprecipitazione di ossalati. Tutti e tre i metodi hanno permesso di sintetizzare con successo ferriti di ferro (per quanto la natura e le caratteristiche dei composti preparati siano variati in base alla tipologia di sintesi scelta). Sono stati ottenuti gli spinelli CoFe2O4, MgFe2O4, MnFe2O4, NiFe2O4 e ZnFe2O4, oltre alle perovskiti MnFeO3 e SrFeO3-δ. Tutti i prodotti sono stati ottenuti come polveri cristalline e (con l'eccezione di MgFe2O4), sotto forma di una singola fase cristallina. I materiali sintetizzati sono stati successivamente caratterizzati, tramite una vasta gamma di tecniche, dal punto di vista composizionale, strutturale e funzionale. In particolare, il rapporto stechiometrico massivo tra i metalli nei composti è stato studiato tramite ICP-AES (Inductively Coupled Plasma-Atomic Emission Spectroscopy) e confrontato con la composizione superficiale ottenuta tramite XPS (X-ray Photoelectron Spectroscopy). Si è fatto uso delle tecniche di microanalisi e TGA-DSC (ThermoGravimetric Analysis-Differential Scanning Calorimetry) per esplorare l'evoluzione del sistema durante la calcinazione, oltre a valutare la presenza di possibili residui organici (dovuti ai precursori utilizzati durante la sintesi) nei materiali. XRD (X-Ray Diffraction) e TPXRD (Temperature-Programmed XRD) sono stati impiegati per studiare la struttura cristallina delle polveri e per calcolare (tramite raffinamento Rietveld) le dimensioni medie dei cristalliti. I dati così ottenuti sono stati confrontati con le immagini acquisite tramite TEM (Transmission Electron Microscopy). Parallelamente, spettroscopia Mössbauer, XPS e TPR (Temperature Programmed Reduction) hanno fornito informazioni sugli stati di ossidazione degli elementi nei materiali (sia in superficie che nel massivo). Nel caso delle ferriti in forma di spinello, la spettroscopia Mössbauer è stata particolarmente utile, in quanto ha permesso di calcolare il grado di inversione dei composti. Dal punto di vista funzionale, misure SQUID (Superconducting Quantum Interference Device) sono state impiegate per studiare le proprietà magnetiche dei materiali, rivelando che gli spinelli di cobalto e manganese presentano (come previsto) un comportamento ferrimagnetico, mentre la perovskite di manganese ha comportamento paramagnetico sopra i 35 K (temperatura di Néel) e ferrimagnetico al di sotto di tale temperatura. Caratterizzazioni dielettriche per ottenere informazioni sulle proprietà di conduzione dei materiali sono state eseguite tramite BES (Broadband Electric Spectroscopy). Queste misure hanno evidenziato rilassamenti a 30 e 90°C negli spinelli di cobalto e nichel, compatibili con l'intercalazione di acqua all'interno della struttura cristallina. Per quanto concerne la perovskite di manganese, i rilassamenti mostrati attorno a 100°C e la maggiore conducibilità rispetto agli spinelli sono compatibili con la conduzione ionica.. L'attività catalitica dei materiali è stata esplorata tramite l'ossidazione a temperatura programmata del metano (CH4-TPO), mostrando che le ferriti sintetizzate contenenti cobalto, manganese e nichel sono attive nell'ossidazione del metano ad anidride carbonica, pur non essendo stabili nel corso di cicli successivi. L'effetto dei parametri di sintesi (quali la natura dei precursori, additivi, parametri termici, tempo di invecchiamento) sulla natura finale (composizionale e strutturale) degli ossidi prodotti è stato oggetto di particolare interesse. Sulla base dei risultati ottenuti da questi studi, è stato possibile ottimizzare ciascun protocollo di sintesi allo scopo di massimizzare resa e purezza dei prodotti, oltre a migliorare le condizioni di sintesi. In particolare, uno degli scopi principali di questo processo di ottimizzazione è stato quello di abbassare le temperature di trattamento e ridurre i tempi di trattamento termico, senza che al contempo questo causasse perdite dal punto di vista della resa e della qualità dei prodotti. In particolare è stato possibile sintetizzare gli spinelli di cobalto, manganese, nichel e zinco per via idrotermale a 75°C con un trattamento di 4 ore. È stata inoltre esplorata la possibilità di applicare il metodo della coprecipitazione degli ossalati da una soluzione acquosa alla preparazione di ferriti di ferro contenenti due metalli. Sono stati sintetizzati con successo, e successivamente caratterizzati, i sistemi Co0.5Mn0.5Fe2O4, Co0.5Mg0.5Fe2O4 e Co0.5Mn0.5FeO3. La misura dei rapporti stechiometrici massivi tra i metalli in ciascuna ferrite (vale a dire Co, Fe e Mg o Mn) ha mostrato che il metodo di sintesi scelto permette un buon controllo sulla stechiometria finale dei materiali preparat

Ferriti di stronzio nanostrutturate: sintesi e caratterizzazione

Due to their important and diverse properties, together with their thermal and mechanical stability, mixed transition metal oxides having perovskite crystal structures have long been object of study and technological applications. In this framework, strontium ferrite SrFeO3-x holds particular interest due to its capability to act as both an electronic and ionic conductor at high temperatures (becoming capable to conduct O2- ions through vacancies in its crystal structure) and thus employable both in fuel cells (as an electrode) and oxygen concentrating devices[1]. Moreover also the magnetic and catalytic properties of this compound are also to be considered. In this work, the perovskite SrFeO3-x has been obtained through coprecipitation. Three synthetic paths have been explored: coprecipitation of hydroxides from an aqueous solution, coprecipitation of oxalates from an aqueous solution and polyol-assisted coprecipitation[2]. Products of all three synthetic paths were analyzed by means of powder XRD and XPS to determine the purity of the sample and to optimize the synthetic process itself. Pure samples were further characterized by means of ICP analysis, nitrogen adsorption, elemental analysis and Mössbauer spectroscopy. In particular, XRD and Mössbauer spectroscopy were used respectively to deduce the crystal structure of the obtained powders and to analyze the oxidation states and magnetic properties of the iron atoms contained in the sample, thus allowing to estimate the magnitude of the defects (as an oxygen vacancy would result in the presence of Fe(III) rather than Fe(IV))

Coprecipitated transition metal ferrites investigated by XPS

In the present contribution, four transition metal ferrites, namely the manganese perovskite MnFeO3 and the nickel, cobalt and zinc spinels NiFe2O4, CoFe2O4, and ZnFe2O4, were investigated through XPS (X-ray Photoelectron Spectroscopy). The synthesis route for the analyzed materials involved the precipitation of metal oxalates from an aqueous solution of metallic salts and oxalic acid. The precipitate was then isolated and calcined at 900\u2009\ub0C in order to obtain the crystalline ferrite powders. Along with survey scans of the analyzed samples, detailed spectra of the O 1s, C 1s, Fe 2p and M 2p (where M = Mn, Ni, Co, Zn depending on the compound in question) regions were collected. The data resulting from these analyses is discussed

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt (CoFe2O4), nickel (NiFe2O4), zinc (ZnFe2O4) and manganese (MnFe2O4) spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of coprecipitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining coprecipitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low temperature of 75 \ub0C and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction (XRPD), while X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy (TEM) observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer (SQUID) revealing hard and soft ferrimagnetic behavior, respectively

Very low temperature wet-chemistry colloidal routes for mono- and polymetallic nanosized crystalline inorganic compounds

The use of low temperature, sustainable processes based on cheap and safe chemicals as well as nontoxic, easy to handle chemicals and solvents is a challenging issue in modern inorganic chemistry; moreover the obtainment of crystalline functional nanostructures at low or even room temperature is the goal of many synthetic efforts. Within this framework, in these last years, we have developed in our group different room or low temperature (T < 150 \ub0C) wet chemistry colloidal routes to prepare different inorganic functional nanomaterials. These compounds range from (1) ferrites to (2) pure and doped metal oxides, sulphides and halogenides, to (3) metal/metal oxide nanocomposites. The adopted wet chemistry routes encompassed (1) miniemulsions, (2) coprecipitation combined with hydrothermal route and (3) more classical colloidal routes, though revised in some critical aspects. This mini-review provides an overview of the main features as well as the pros and cons of the proposed routes for the obtainment of targeted inorganic systems for applications in optical bioimaging or in energy applications. It not only summarises already published work, but also presents some exciting perspectives disclosed by performed studies and past experience as well as comparisons with state-of-the-art research