Neutron diffraction study of the interaction of iron with amorphous fullerite

The amorphous fullerite C₆₀ has been prepared by mechanical activation (grinding in a ball mill), and its interaction with iron during sintering of powders with 0–95 at % Fe has been studied. After sintering in the range 800–1200°C under a pressure of 70 MPa, the samples have nonequilibrium structures different from the structures of both annealed and quenched steels. In this case, the carbon phase, i.e., amorphous fullerite, undergoes a polyamorphous transition to amorphous graphite. It has also been shown that the interaction of amorphous fullerite with iron is weaker compared to crystalline fullerite or crystalline graphite.     

A magnetic and Mössbauer study of melt-spun Nd60Fe30Al10

Nd₆₀Fe₃₀Al₁₀ alloys were rapidly quenched by the melt-spinning technique with different wheel surface speeds ranging from 5 to 30 m/s. The microstructure and the magnetic properties were strongly dependent on the quenching rate. A high quenching rate led to an amorphous structure with a low coercivity at room temperature, while a mixture of amorphous and crystalline phases was found after melt-spinning at 5 m/s, which exhibited hard magnetic properties at room temperature. For both the ribbons melt-spun at 5 and 30 m/s respectively, coercivity increased with decreasing temperature and reached a maximum at around 50 K. Maximum magnetization at 10 T increased dramatically at low temperature. Our magnetic study has shown that the presence of crystalline Nd was responsible for the increase of magnetization and the decrease of coercivity, as Nd became magnetically ordered at low temperatures. The Mössbauer study has shown that the magnetic microstructures of melt-spun ribbons were not uniform, as the spectra needed to be fitted by magnetic and non-magnetic components.     

Unusual magnetization anisotropy in amorphous Nd–Fe–Al ribbons

Nd₆₀Fe₃₀Al₁₀ ribbons has been prepared by chill-block melt-spinning with different wheel speeds from 5 to 30 m/s. Fully amorphous ribbons were obtained at wheel speeds of 25 and 30 m/s. These ribbons exhibited an unusually large anisotropy in magnetization. The effect of the magnetic anisotropy decreased with decreasing wheel speed, and nearly disappeared at the wheel speed of 5 m/s, at which the ribbon consisted of a mixture of a more stable Fe-rich amorphous phase and a crystalline Nd phase with a strong crystallographic texture.     

Effect of nanocrystallization on the electronic conductivity of vanadate–phosphate glasses

Electronically conducting glasses of the composition xV₂O₅·(100 − x)P₂O₅ for 60 < x < 90 were prepared. The glasses of the composition corresponding to x = 90 exhibited the highest electrical conductivity and they were studied in more detail. The effects of the annealing of the samples on their electrical conductivity, structure and other characteristics were studied by impedance spectroscopy, X-ray diffractometry, DSC and SEM microscopy. It was shown that, at temperatures close to the crystallization temperature T_c (determined from DSC), these glasses turned into nanomaterials consisting of crystalline grains of V₂O₅ (average size 25–35 nm) embedded in the glassy matrix. Their electrical conductivity was higher and the temperature stability was better than those of the starting glasses. It is postulated that the major role in this conductivity enhancement is played by the interfacial regions between crystalline and amorphous phases. The annealing at temperatures exceeding T_c led to massive crystallization and to a conductivity drop. The XRD and SEM observations have shown that the material under study undergoes structural changes: from amorphous at the beginning, to partly crystalline after the annealing at 340 °C and to polycrystalline after the annealing at 530 °C.The obtained results are in agreement with those of our earlier studies on mixed electronic–ionic conducting glasses of the ternary Li₂O–V₂O₅–P₂O₅ system.     

Preparation of carbon nanoparticles from electrolysis of molten carbonates and use as anode materials in lithium-ion batteries

The electrochemical reduction of molten Li–Na–K carbonates at 450 °C provides “quasi-spherical” carbon nanoparticles with size comprised between 40 and 80 nm (deduced from AFM measurements). XRD analyses performed after washing and heat-treatment at various temperatures have revealed the presence of graphitised and amorphous phases. The d₀₀₂ values were close to the ideal one obtained for pure graphite. Raman spectroscopy has pointed out surface disordering which increases with increasing temperature of the heat-treatment. The presence of Na and Li on the surface of the carbon powder has been evidenced by SIMS. The maximum Na and Li contents were observed for carbon samples heat-treated at 400 °C. Their electrochemical performances vs. the insertion/deinsertion of lithium cations were studied in 1 M LiPF₆–EC : DEC : DMC (2 : 1 : 2). The first charge–discharge cycle is characterised by a high irreversible capacity as in the case of hard-disordered carbon materials. However, the potential profile in galvanostatic mode is intermediate between that usually observed for graphite and amorphous carbon: rather continuous charge–discharge curves sloping between 1.5 and 0.3 V vs. Li / Li⁺, and successive phase transformations between 0.3 and 0.02 V vs. Li / Li⁺. The best electrochemical performances were obtained with carbon powders heat-treated at 400 °C which exhibits a reversible capacity value of 1080 mAh g^− 1 (composition of Li_2.9C₆). This sample has also both the lowest surface disordering (deduced from Raman spectroscopy), and the highest Na and Li surface contents (deduced from SIMS).     

The investigation of transport properties of mesoscopic graphite in high magnetic field

The electrical transport properties of mesoscopic graphite have been investigated in a gate voltage configuration. Few layer graphene structures made from Kish graphite exhibit Shubnikov-de Haas (SdH) oscillations in magnetic fields up to 33 T, with a strong gate voltage dependence. A two band model can be used to explain the linear dependence of the SdH frequency on the gate voltage. The temperature dependence of the SdH oscillation amplitude allows the determination of the effective masses of the carriers, which remain comparable between mesoscopic and bulk graphite samples. However, mesoscopic graphite thinner than 130 nm does not exhibit the field induced charge density wave transition seen in bulk samples above 25 T at low temperatures.     

A new carbon nitride synthesized by shock compression of organic precursors

A series of shock recovery experiments up to ∼50 GPa were carried out on three nitrogen-rich materials of a C–N–O amorphous precursor, dicyandiamide and melamine. The powder X-ray diffractions (XRD) of recovered samples show that carbon nitride phases are formed. They are β-C₃N₄ and a new crystalline phase. The new phase is indexed as a monoclinic cell with a=0.981 nm, b=0.723 nm, c=0.561 nm, β=95.2° and V_cell=0.3966 nm³. Melamine was very stable and did not decompose up to ∼37 GPa. This new phase is considered to form during the adiabatic release process with an extremely high quenching rate (∼10⁹ K/s) and shock compression may provide a novel synthesis route for various C–N phases from appropriate organic materials.     

Microstructural properties of plasma-enhanced chemical vapor deposited WNx films using WF6–H2–N2 precursor system

A WF₆–H₂–N₂ precursor system was used for plasma-enhanced chemical vapor deposition (PECVD) of WN_x films. We examined the microstructural changes of the WN_x films depending on N₂/H₂ flow-rate ratio and post-annealing (600–800 °C for 1 h). As the N₂/H₂ flow rate was increased from 0 to 1.5, as-deposited WN_x films exhibited various different crystalline states, such as nanocrystalline and/or amorphous structure comprising W, WN, and W₂N phases, a fine W₂N granular structure embedded in an amorphous matrix, and a crystalline structure of β-W₂N phase. After post-annealing above 600 °C, crystalline recovery with phase separation to β-W₂N and α-W was observed from the WN_x films deposited at an optimized deposition condition (flow-rate ratio = 0.25). From this PECVD method, an excellent step coverage of ∼90% was obtained from the WN_x films at a contact diameter of 0.4 μm and an aspect ratio of 3.5.     

Control of crystalline phases in magnetic Fe nanoparticles inserted inside a matrix of porous carbon

Two magnetic composites made up of Fe nanoparticles (Fe-NPs) embedded in a porous amorphous carbon matrix are presented. One of the samples, Fe-S-AC, was obtained with the aid of sucrose and the other, Fe-AC, in the absence of this substance. The XRD patterns show Bragg diffraction peaks associated with α-Fe and γ-Fe crystalline phases in the Fe-AC sample, while only peaks corresponding to the α-Fe phase are observed for Fe-S-AC powders. The Fe-NPs exhibit broad particle-size distributions for both samples, 5–50 nm for Fe-AC, whereas two populations (2–8 and 10–70 nm) for the Fe-S-AC composite are found. This fact gives rise to poorly defined blocking temperatures, as it can be deduced from the broad maxima observed in M_ZFC(T) variations. In addition, M(H) curves for both Fe-AC and Fe-S-AC samples reveal the existence of exchange-bias effect for T<60 K, probably due to a magnetic coupling within a core/shell structure of the Fe-NPs, although this effect was observed to be less significant for Fe-S-AC.     

Investigations on the sulphur incorporation in sputtered Cu,In multilayer precursors

High quality CuInS₂ layers have been grown using a two step process. Multiple Cu, In bilayers were deposited by RF magnetron sputtering on Mo-coated glass substrates followed by sulphurisation using elemental sulphur in a closed graphite box at different temperatures up to 550°C. The layers were characterised to study their structure and composition using XRD, SEM and EDAX. More sulphur was incorporated at lower annealing temperatures with sulphur content higher than 50 at.%, while the Cu/In ratio ranges between 0.9 to 1.1. As the annealing temperature increases beyond 400°C, the composition of sulphur decreases to 46 at.% with an incorporation of Mo in the layers. The secondary phases observed at different annealing temperatures were identified and reported. Polycrystalline, single phase and densely packed CuInS₂ layers with (1 1 2) preferred orientation were obtained for annealing temperatures of about 350°C.     

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.     

Densification and microstructure of lead zirconate titanate ceramics fabricated from a triol sol–gel powder

Lead zirconate titanate (PZT) nano-powder was prepared by a triol sol–gel process. X-ray diffraction and transmission electron microscopy results showed that as-synthesized amorphous powder started to crystallize at the calcination temperature above 500 °C. The crystalline powder was formed into pellets and sintered at temperatures between 900 and 1300 °C. Co-existence of tetragonal and rhombohedral phase was observed in all ceramics. Microstructural investigation of PZT ceramics showed that uniform grain size distribution with average grain size of ∼0.8–2.5 μm were received with sintering temperature up to 1200 °C. Further increasing the temperature caused abnormal grain growth with the grain as large as 13.5 μm. An attempt to optimize densification with uniform grain size distribution was also performed by varying heating rate and holding time during sintering. It was found that dense (∼97%) sol–gel derived PZT ceramic with uniform microstructure was achieved at 1100 °C with a heating rate of 5 °C min⁻¹ and 6 h dwell time.     

Magnetic properties of nanocrystalline Fe86.7Zr3.3B4Ag6 thin film

The changes of magnetic properties with annealing temperature were studied in the amorphous Fe_86.7Zr_3.3B₄Ag₆ thin film. The thin films were deposited by a DC magnetron sputtering method, annealed at 300–700°C for 1 h in vacuum under a field of 1.5 kOe parallel to the film plane, and then furnace-cooled. As a result, it has been found that the Ag addition to Fe–Zr–B amorphous thin films resulted in the decrease of crystallization temperature to 400°C due to promoted crystallization ability. Also, it gave rise to formation of fine BCC α-Fe crystalline precipitates with a grain size smaller than 10 nm in the amorphous matrix near 400°C, and led to prominent enhancement in the magnetic properties of the Fe_86.7Zr_3.3B₄Ag₆ thin films. Significantly, excellent magnetic properties such as a saturation magnetization of 1.7 T, a coercive force of 1 Oe and a permeability of 7800 at 50 MHz were obtained in the amorphous Fe_86.7Zr_3.3B₄Ag₆ thin film containing 7.2 nm-size BCC α-Fe, which was annealed at 400°C. Also, core loss of 1.4 W cm⁻³ (B_m=0.1 T) at 1 MHz in the thin film was obtained, and it is a much lower value than had been obtained in any existing soft magnetic materials. Such excellent properties are inferred to originate from the uniform dispersion of nano-size BCC α-Fe in the amorphous matrix.     

Cavitation milling of natural cellulose to nanofibrils

Cavitation holds the promise of a new and exciting approach to fabricate both top down and bottom up nanostructures. Cavitation bubbles are created when a liquid boils under less than atmospheric pressure. The collapse process occurs supersonically and generates a host of physical and chemical effects. We have made an attempt to fabricate natural cellulose material using hydrodynamic as well as acoustic cavitation. The cellulose material having initial size of 63 micron was used for the experiments. 1% (w/v) slurry of cellulose sample was circulated through the hydrodynamic cavitation device or devices (orifice) for 6 h. The average velocity of the fluid through the device was 10.81 m/s while average pressure applied was 7.8 kg/cm². Cavitation number was found to be 2.61. The average particle size obtained after treatment was 1.36 micron. This hydrodynamically processed sample was sonicated for 1 h 50 min. The average size of ultrasonically processed particles was found to be 301 nm. Further, the cellulose particles were characterized with X-ray diffraction (XRD) and differential scanning calorimetry (DSC) to see the effect of cavitation on crystallinity (X_c) as well as on melting temperature (T_m). Cellulose structures consist of amorphous as well as crystalline regions. The initial raw sample was 86.56% crystalline but due to the effect of cavitation, the crystallinity reduced to 37.76%. Also the melting temperature (T_m) was found to be reduced from 101.78 °C of the original to 60.13 °C of the processed sample. SEM images for the cellulose (processed and unprocessed) shows the status and fiber–fiber alignment and its orientation with each other. Finally cavitation has proved to be very efficient tool for reduction in size from millimeter to nano scale for highly crystalline materials.     

High lithium ion conductivity glass-ceramics in Li2O–Al2O3–TiO2–P2O5 from nanoscaled glassy powders by mechanical milling

Mechanical milling (MM) has been used to prepare the nanosized Li_1.4Al_0.4Ti_1.6(PO₄)₃ (denoted LATP) glassy powders, which was converted into glass-ceramics through thermal treating at 700–1000 °C. The XRD, TEM, FESEM and ac impedance techniques were used to characterize the products. The results showed that completely amorphous products were prepared by MM for 40 h, and single-phase LiTi₂(PO₄)₃-type structured glass-ceramics were obtained by further heat treatment. The lithium ion conductivity of the glass-ceramics increased with the growth of the crystalline phase and decrease of the grain size. The highest bulk conductivity (σ_b) of 1.09 × 10^− 3 S cm^− 1 with an energy of activation as low as 0.28 eV was obtained at room temperature for the specimen treated at 900 °C for 6 h. The high conductivity, easy fabrication and low cost make the LATP glass-ceramics promising to be used as inorganic solid electrolyte for all-solid-state Li-ion rechargeable batteries.     

Effect of ultrasound energy on the zeolitization of chemical extracts from fused coal fly ash

This paper investigates the effects of ultrasound (UTS) energy at different temperatures on the zeolitization of aluminosilicate constituents of coal fly ash. UTS energy irradiated directly into the reaction mixture utilizing a probe immersed into the reaction mixture, unlike previously reported works that have used UTS baths. Controlled synthesis was also conducted at constant stirring and at the same temperatures using conventional heating. The precursor reaction solution was obtained by first fusing the coal fly ash with sodium hydroxide at 550 °C followed by dissolution in water and filtration. The synthesized samples were characterized by XRF, XRD, SEM and TGA. The crystallinity of crystals produced with UTS assisted conversion compared to conventional conversion at 85 °C was twice as high. UTS energy also reduced the induction time from 60 min to 40 min and from 80 min to 60 min for reaction temperatures of 95 °C and 85 °C, respectively. Prolonging the UTS irradiation at 95 °C resulted in the conversion of zeolite-A crystals to hydroxysodalite, which is a more stable zeolitic phase. It was found that at 85 °C coupled with ultrasound energy produced the best crystalline structure with a pure single phase of zeolite-A. It has been shown that crystallization using UTS energy can produce zeolitic crystals at lower temperatures and within 1 h, dramatically cutting the synthesis time of zeolite.     

Dense stripe domains in a nanocrystalline CoFeSiB thin film

We recently reported a possible antiferromagnetically coupled phase in a Co-rich CoFeSiB thin film, that had a partially nanocrystalline Co phase in an amorphous CoFeSiB matrix. Although an amorphous CoFeSiB film should show a ferromagnetic behavior, we observed an antiferromagnetic coupling associated with a nanocrystalline Co phase in the hysteresis-loop measurements of Co-rich CoFeSiB thin films. We ascribed the observed antiferromagnetic coupling to dense stripe domains consisting of periodically up and down domains perpendicular to the surface of the film. The configuration of the stripe domains was confirmed with magnetic force microscopy images. When a longitudinal magnetic field was applied, the size of the stripe domain was reduced. While for a transverse field, the domain structure became tilted and zigzagged, but no in-plane magnetic anisotropy was noted. When the magnetic field was increased to values above the saturation magnetic field, H_S = 2.5 kOe, the domain structure disappeared.     

Nanocrystalline diamond thin films deposited by 35 kHz Ar-rich plasmas

We give evidence of nanometric size (5–15 nm) crystalline diamonds in carbon thin films obtained at low substrate temperature (15 °C) under the action of low pressure (0.1–0.3 Torr) 35 kHz excited CH₄/Ar (80–95%) plasmas. The decrease in Ar concentration was found to lead to higher film hardness while crystalline nanodiamonds are observed in a wide interval (1–3.5 h) of deposition times but only for very high Ar concentration (95%). The polycrystalline nanodiamond grains are found over 10–20% within an amorphous carbon matrix. It is suggested that the distribution of nanodiamond grains might be connected to the nonuniform ion energy distribution in the Ar-rich plasma generated at 35 kHz. Morphological and structural features of the deposited films were also investigated.     

Giant magneto-impedance effect in CoMnSiB amorphous microwires

The giant magneto-impedance (GMI) ratio, ΔZ/Z=[(Z(H)−Z(H_max)]/Z(H_max), in a nearly zero magnetostrictive Co_68.5Mn_6.5Si₁₀B₁₅ amorphous microwire has been investigated for the frequency range 0.5–10 MHz, driving current amplitude of 0.5–2.5 mA, bias DC magnetic field up to 2400 A/m and under applied tensile stress up to 132 MPa. A maximum relative change in the GMI ratio up to around 130% is observed at a frequency of 10 MHz, magnetic DC field of about 180 A/m, driving current amplitude of 1 mA and under tension of 60 MPa. The tensile stress dependence of the magnetic field, H_m, corresponding to the maximum ΔZ/Z ratio allows to estimate the magnetostriction constant (λ_s≈−2×10⁻⁷) to be in good agreement with λ_s values estimated by different methods and in amorphous alloys with similar compositions.     

Synthesis and investigations on the stability of La0.8Sr0.2CuO2.4+δ at high temperatures

For application in solid oxide fuel cells La_0.8Sr_0.2CuO_2.4+δ was synthesized and the phase evolution was characterized after quenching from different temperatures and after slow cooling. A single phase perovskite was found after quenching from 950 °C. The electrical conductivity of the La_0.8Sr_0.2CuO_2.4+δ perovskite exhibited metallic behavior reaching values of about 270 S/cm at 800 °C in air. The thermal expansion between 30 and 800 °C gave a thermal expansion coefficient of 11.1 × 10^− 6 K^− 1.At higher temperatures, the perovskite was transformed to the K₂NiF₄-type structure via an intermediate stage that can be best described as a LaSrCuO₄ phase with preferential growing of {020} lattice planes. After sintering at 1100 °C and slow cooling in the furnace a phase mixture of (La,Sr)CuO_4+δ and (La,Sr)CuO_2.4+δ perovskite was obtained. This phase mixture showed higher electrical conductivity (400 S/cm at 800 °C) and smaller thermal expansion coefficient (9.6 × 10^− 6 K^− 1) than the single phase La_0.8Sr_0.2CuO_2.4+δ perovskite.