Effect of milling time and heat treatment on the composition of CuIn<Subscript>0.75</Subscript>Ga<Subscript>0.25</Subscript>Se<Subscript>2</Subscript> nanoparticle precursors and films

Preparation of pure phase CuIn_0.75Ga_0.25Se₂ nanoparticle powder by ball milling technique has been confirmed for the milling time of more than 45 min at 1200 rpm. Formation of shear bands responsible for breakdown of grains and generation of nanostructure during mechanical alloying, dislocation and defects induced due to milling has been studied by High-Resolution Transmission Electron Microscopy (HRTEM) analysis. Deviation in final composition of the products from those of starting materials has been discussed based on low volatilization of Se. Effect of milling time on the phase formation, particle size, and composition has been discussed in detail. Decrease in grain size from 12.44 to 7.96 nm has been observed with the increase in milling time. Mechanically induced self-propagating reaction mechanism which occurred during milling process is also discussed. Nanoparticle precursor was mixed with organic binder material for rheology of mixture to be adjusted for screen printing, and the films are subjected to heat treatment at five different temperatures in nitrogen ambient for 25 min. Average grain size calculated by Scherrer’s formula was almost the same irrespective of temperature. Reproducibility of precursor composition in the deposited films has been discussed in detail.     

One-step fastest method of nanocrystalline CuAlS<Subscript>2</Subscript> chalcopyrite synthesis,and its nanostructure characterization

Nanocrystalline CuAlS₂ chalcopyrite has been mechanosynthesized at room temperature for the first time by ball milling the stoichiometric mixture of elemental of Cu, Al, and S powders under argon atmosphere. Initially, the CuAlS₂ phase is formed by solid state reaction of elemental powders within 15 min of milling and in the course of milling crystallite size decreases slowly to ~5 nm within 10 h of milling. Microstructure characterization and phase transformation kinetics of the elemental powders toward the chalcopyrite phase formation has been made by employing the Rietveld analysis using X-ray diffraction data of unmilled and ball-milled samples.     

Disintegration of a coarse-grained vanadium monoxide VO<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript> powder

A coarse-grained powder of nonstoichiometric cubic vanadium monoxide VO _y is disintegrated in a Retch PM 200 planetary ball mill. Milling of the coarse-grained vanadium monoxide powder VO _y at a rate of rotation of 500 rpm for 2 h significantly broadens diffraction lines, and the crystal structure of vanadium monoxide VO_1.00 after milling remains the same. High-resolution scanning electron microscopy and X-ray diffraction studies of the microstructure of vanadium monoxide demonstrate that high-energy milling can produce vanadium monoxide powders with an average crystallite size of 23 ± 10 nm. The vanadium monoxide produced by milling has a crystallite size that is half the crystallite size in the titanium monoxide produced by severe plastic deformation.     

Preparation and properties of Zn<Subscript>0.9</Subscript>Ni<Subscript>0.1</Subscript>O diluted magnetic semiconductor nanoparticles

With a view to study the structural, electronic, magnetic, and electrical properties of Zn_0.9Ni_0.1O diluted magnetic semiconductor nanoparticles, systematic investigation has been undertaken. Samples were prepared for the first time by hydrazine-assisted polyol method, and the powders were annealed at various temperatures in order to obtain the samples with different grain sizes. From the Rietveld refined XRD data, lattice parameters, the average crystallite size values, and r.m.s micro-strain values were computed. From the AFM and TEM studies, the average particle sizes were obtained and are found to be in the range 12–46 nm. XPS measurements clearly indicate that the chemical states as +2 for both Zn and Ni ions and are stable with varying annealing temperature. Further, using XPS and optical studies, the electronic structure of the materials was analyzed. A careful phase analysis of the Rietveld refined XRD data (at logarithmic scale) selected area electron diffraction patterns, FTIR, Raman, and XPS studies; it was concluded that all the samples are having hexagonal wurtzite structure without any detectable impurity phases. The optical band gap values are found to exhibit a clear blue shift. The influence of oxygen vacancies on the emission spectra was studied by Photo Luminescence measurement. The magnetization studies were undertaken by VSM, MFM, and FMR techniques and confirmed the presence of clear room temperature ferromagnetism without any magnetic clusters. The carrier concentration (n) values obtained from the thermo power studies are found to decrease with increasing annealing temperature and depend on the local defects which are critically influenced by the annealing temperature and crystallite size of the nanomaterials.     

Morphology modification of TiO<Subscript>2</Subscript> nanotubes by controlling the starting material crystallite size for chemical synthesis

TiO₂ nanotubes (NTs) were prepared by low-temperature chemical synthesis using anatase TiO₂ particles with different crystallite sizes in a NaOH solution followed by water washing and HCl neutralization. The synthesized TiO₂ NTs showed diverse morphologies depending on the starting materials. The crystallite size of TiO₂ raw materials increased with an increase in annealing temperature, and larger TiO₂ NTs, around 31 nm in diameter, were obtained from large raw powder with a crystallite size of 117 nm. X-ray diffraction and Raman spectroscopy revealed that the obtained TiO₂ NT exhibited lower crystallinity; however, Raman vibration seems to be more likely than a rutile structure.     

Structural evolutions of the mechanically alloyed Al<Subscript>70</Subscript>Cu<Subscript>20</Subscript>Fe<Subscript>10</Subscript> powders

Elemental mixtures of Al, Cu, Fe powders with the nominal composition of Al₇₀Cu₂₀Fe₁₀ were mechanically alloyed in a planetary ball mill for 80 h. Subsequent annealing of the as-milled powders were performed at 600–800°C temperature range for 4 h. Structural characteristics of the mechanically alloyed Al₇₀Cu₂₀Fe₁₀ powders with the milling time and the heat treatment were investigated by X-ray diffraction (XRD), differential scanning calorimeter (DSC) and differential thermal analysis (DTA). Mechanical alloying of the Al₇₀Cu₂₀Fe₁₀ did not result in the formation of icosahedral quasicrystalline phase (i-phase) and a long time milling resulted in the formation of β-Al(Cu,Fe) solid solution phase (β-phase). The i-phase was observed only for short-time milled powders after heat treatment above 600°C. The β-phase was one of the major phases in the Al₇₀Cu₂₀Fe₁₀ alloy. The w-Al₇Cu₂Fe₁ phase (w-phase) was obtained only after heat treatment of the short-time milled and unmilled samples. The present investigation indicated that a suitable technique to obtain a large amount of quasicrystalline powders is to use a combination of short-time milling and subsequent annealing.     

Preparation of Y<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript> pyrochlore using high-energy ball milling and their structural,thermal and conducting properties

Pyrochlore-structured materials are very important materials due to their structural and conducting properties. These properties can be further modified by changing processing conditions. In the present study, pyrochlore (Y₂Ti₂O₇) is synthesized using high-energy ball milling. During various stages of ball milling, the ball-milled powder is taken for investigating the structural and thermal properties. The replacement of Ti₂O₃ by TiO₂ in nominal composition leads to lower ball milling duration to form Y₂Ti₂O₇. Differential thermal analysis showed the single exothermic peak below 800 °C, which indicates formation of disordered pyrochlore phase. The as prepared powders (40-h ball milled) were compacted and heat treated at 1,450 °C for 12 h. The conductivity of sintered sample is found to be one order higher than earlier reported pure Y₂Ti₂O₇ pyrochlore.     

Temperature dependence of the lowest frequency <Emphasis Type="BoldItalic">E</Emphasis><Subscript><Emphasis Type="Bold">g</Emphasis></Subscript> Raman mode in laser-synthesized anatase TiO<Subscript>2</Subscript> nanopowder

Nanosized titanium dioxide (TiO₂) powder was prepared by a laser-induced pyrolysis. Specific surface area of the as-grown powder measured by BET method was 109 m²/g. The grain size (14.5 nm) estimated from these data coincides well with the crystallite size (12.3 nm) determined by XRD measurements. The average grain size (∼35 nm) obtained from the subsequent SEM measurements refers to considerable agglomeration of nanoparticles. Raman spectroscopy has been used to investigate the structural properties of TiO₂ nanopowder and its anatase structure is confirmed. The blueshift and broadening of the lowest frequency E_g Raman mode at temperature range ∼25–550 K have been analyzed using a phonon-confinement model. Dominant influence of the strong anharmonic effect at higher temperatures was demonstrated. PACS 81.07.Wx; 78.30.-j; 63.22.+m     

Magnetic and dielectric properties of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.8</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> nanoparticles synthesized by PEG-assisted hydrothermal method

We present a systematic investigation on the structural and magnetic properties of Mn_0.2Ni_0.8Fe₂O₄ nanoparticles synthesized by a polyethylene glycol (PEG)-assisted hydrothermal route. XRD, FT-IR, TEM and VSM were used for the structural, morphological, dielectric properties and magnetic investigation of the products, respectively. Average crystallite size of product was estimated using Line profile fitting as 6 ± 1 nm and particle size as 6.5 ± 1.0 nm from TEM micrographs. Magnetization measurements have shown that the particles have a blocking temperature of 134 K. Magnetization and the coercive field of the sample increase by decreasing the temperature. The conductivity measurements reveal the semiconducting behaviour for the sample. Temperature-dependent dielectric properties: dielectric permittivity (ε) and ac conductivity (σ_ac) for the sample were studied as a function of applied frequency in the range from 1 Hz to 3 MHz. These studies indicated that the dielectric dispersion curve for the sample showed usual dielectric dispersion which can be explained on the basis of Koop’s theory, which is based on the Maxwell–Wagner model for the interfacial polarization of homogeneous double structure.     

Mechanochemical reactions in Co<Subscript>80</Subscript>B<Subscript>20</Subscript> and Co<Subscript>60</Subscript>B<Subscript>40</Subscript> mixtures during ball milling and postannealing

The solid-phase interaction of cobalt with boron during high-energy ball milling of Co₈₀B₂₀ and Co₆₀B₄₀ mixtures was studied. It was found that Co₃B boride forms during the mechanical alloying of components in the presence of both modifications of Co with a reduction in the size of blocks of up to 7–15 nm. The transformation of the metastable Co₃B phase into stable Co₂B and CoB borides is observed in the temperature range of 590–700°C.     

Growth of AgInSe<Subscript>2</Subscript> on Si(100) substrate by thermal evaporation technique

AgInSe₂ films were prepared by a thermal evaporation technique onto Si(100) substrates at a pressure of 10⁻⁵ mbar. Structural and optical properties of films deposited at 300 and 473 K have been investigated. The film composition was studied by energy dispersive analysis through X-rays. X-ray diffraction patterns indicate that AgInSe₂ films have chalcopyrite structure with strong preferred orientation in the (112) direction. Average vertical crystallite size of 25 nm was observed. The optical energy gaps of 1.20 and 1.90 eV were obtained due to the fundamental absorption edge and a transition originating from crystal field splitting, respectively. Field emission scanning electron microscopy shows loosely packed grains of spherical symmetry with some facets.     

Synthesis,structural and electrical properties of double perovskite Sr<Subscript>2</Subscript>NiMoO<Subscript>6</Subscript> ceramics

The double perovskite Sr₂NiMoO₆ powders and ceramics were prepared by two different (conventional and precursor) solid-state reaction methods. The phase structure was characterized by XRD and TEM techniques. It has been indicated that single-phase perovskite powders were obtained when calcined in air at 1300°C. However, nano-particles of the size 30–60 nm have been found in powders prepared with the precursor method, while those from the conventional route exhibit large irregular shaped particles with aggregation. The dielectric properties (ε _r and tanδ) were also examined in the sintered ceramics. The results showed the transition point at 280°C for conventional route, while no clear phase change was observed in ceramics from the precursor route. These observations clearly indicate that the different starting processes affected the phase formation behavior and the electrical properties of Sr₂NiMoO₆ ceramics.     

The magnetic and hyperthermia studies of bare and silica-coated La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> nanoparticles

The magnetic nanoparticles of La_0.75Sr_0.25MnO₃ perovskite manganite with a controlled size were prepared via sol–gel procedure, followed by thermal treatment and subsequent mechanical processing of the resulting raw product. The prepared materials were structurally studied by the XRD and TEM methods and probed by DC magnetic measurements. The nanoparticles of the mean crystallite sizes 11–40 nm exhibit T _C in the range of ≈310–347 K and the sample possessing 20-nm crystallites was identified as the most suitable for hyperthermia experiments. In order to obtain a colloidally stable suspension and prevent toxic effects, the selected magnetic cores were further encapsulated into silica shell using tetraethoxysilane. The detailed magnetic studies were focused on the comparison of the raw product, the bare nanoparticles after mechanical processing and the silica-coated nanoparticles, dealing also with effects of size distribution and magnetic interactions. The heating experiments were carried out in an AC field of frequencies 100 kHz–1 MHz and amplitude 3.0–8.9 kA m⁻¹ on water dispersions of the samples, and the generated heat was deduced from their warming rate taking into account experimentally determined thermal losses into surroundings. The experiments demonstrate that the heating efficiency of the coated nanoparticles is generally higher than that of the bare magnetic cores. It is also shown that the aggregation of the bare nanoparticles increases heating efficiency at least in a certain concentration range.     

Impedance spectroscopy study of Pb<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript> compound

The lead pyrophosphate, Pb₂P₂O₇, compound was prepared by conventional solid-state reaction and identified by X-ray powder diffractometer. Pb₂P₂O₇ has a triclinic structure whose electrical properties were studied using impedance spectroscopy technique. Both impedance and modulus analysis exhibit the grain and grain boundary contribution to the electrical response of the sample. The temperature dependence of the bulk and grain boundary conductivity were found to obey the Arrhenius law with activation energies E _g = 0.66 eV and E _gb = 0.67 eV, respectively. The scaling behavior of the imaginary part of the complex impedance suggests that the relaxation describes the same mechanism at various temperatures.     

Properties of powders produced by evaporating CeO<Subscript>2</Subscript>/Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> targets exposed to pulsed-periodic radiation of a CO<Subscript>2</Subscript> laser

The characteristics (phase composition, grain shape, grain size distribution, and specific surface area) of Ce_0.78Gd_0.22O_2-δ nanopowders produced by exposing the target to pulsed CO₂ laser radiation are reported. Reasons for a threefold increase in the output of the experimental powder-preparation unit (up to 60 g/h) with the characteristic grain size (≈10 nm) remaining unchanged are discussed.     

Effect of PVA addition on formation of spray-deposited Sm<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>CoO<Subscript>3</Subscript> thin films on CeO<Subscript>2</Subscript> substrates

Nano-crystalline films of Sm_0.5Sr_0.5CoO₃ (SSC) have been formed on CeO₂ substrates by spraying stoichiometric aqueous solution containing Sm, Sr, and Co ions. Effect of polyvinyl alcohol (PVA) addition as a complexing agent in spray solution on stoichiometry, crystallite size, morphology, and transport properties of film are studied. The results showed that the SSC cathode had maximum crystallite size for 40% PVA addition. Electrical performance of film decreases with decrease in the particle size, while the electronic to ionic predominance transition temperature decreases with decreasing particle size. These films are studied for their potential application as a cathodic material in developing intermediate temperature solid oxide fuel cells.     

Impedance investigation on porous Sr-doped LaMnO<Subscript>3</Subscript> films onto Sr-Mg-doped LaGaO<Subscript>3</Subscript> electrolyte

The use of Sr-Mg-doped LaGaO₃ (LSGM), a highly conducting oxygen ion electrolyte, in intermediate temperature solid oxide fuel cells (IT-SOFC) technology requires suitable electrode materials. Because the Sr-doped LaMnO₃ (LSM) cathode coupled with the YSZ electrolyte had shown relatively good performances, it has been also suggested for LSGM-based cells. As cathode overpotential is the main performance limitation, the optimization of the LSM/LSGM interface might be of fundamental relevance in the technology development of LSGM-based IT-SOFC. LSM films with different porosities were screen printed on both faces of the LSGM pellets; their morphology and electrical properties were investigated by scanning electron microscopy and impedance spectroscopy, respectively. Porosity was induced by the addition of icing sugar (3–5 wt%) to the LSM powder during ink preparation. Homogeneous electrode layers with a thickness of about 30 μm were obtained. The higher the sugar amount, the higher the film porosity and the lower the LSM grain size. The Nyquist plots show two low frequency arcs to which the charge transfer and mass transfer process or oxygen dissociation process were associated, respectively. One can expect that the best electrochemical performances are obtained using highly porous electrode. Paper presented at the 11th EuroConference on the Science and Technology of Ionics, Batz-sur-Mer, Sept. 9–15, 2007.     

Influence of carbon additive on the properties of spherical Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> and LiFePO<Subscript>4</Subscript> materials for lithium-ion batteries

Preparing spherical particles with carbon additive is considered as one effective way to improve both high rate performance and tap density of Li₄Ti₅O₁₂ and LiFePO₄ materials. Spherical Li₄Ti₅O₁₂/C and LiFePO₄/C composites are prepared by spray-drying–solid-state reaction method and controlled crystallization–carbothermal reduction method, respectively. The X-ray diffraction characterization, scanning electron microscope, Brunauer–Emmett–Teller, alternating current impedance analyzing, tap density testing, and electrochemical property measurements are investigated. After hybridizing carbon with a proper quantity, the crystal grain size of active materials is remarkably decreased and the electrochemical properties are obviously improved. The Li₄Ti₅O₁₂/C and LiFePO₄/C composites prepared in this work are spherical. The tap density and the specific surface area are as high as 1.71 g cm⁻³ and 8.26 m² g⁻¹ for spherical Li₄Ti₅O₁₂/C, which are 1.35 g cm⁻³ and 18.86 m² g⁻¹ for spherical LiFePO₄/C powders. Between 1.0 and 3.0 V versus Li, the reversible specific capacity of the Li₄Ti₅O₁₂/C is more than 150 mAh g⁻¹ at 1.0-C rate. Between 2.5 and 4.2 V versus Li, the reversible capacity of the LiFePO₄/C is close to 140 mAh g⁻¹ at 1.0-C rate.     

Peroxide-based route assisted with inverse microemulsion process to well-dispersed Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> nanocrystals

Well-dispersed bismuth titanate (BIT) nanocrystals with an average size ranged from 3 to 60 nm were synthesized via a peroxide-based route assisted with an inverse microemulsion process. The crystallite size and lattice parameter of BIT upon variable-temperature were determined by X-ray diffraction (XRD). The particle size was confirmed by transmission electron microscopy (TEM). Thermal decomposition behaviour of Ti-peroxy and BIT gel and crystallization kinetics of BIT nanocrystals were investigated by differential scanning calorimetry/thermogravimetry (DSC/TG) and Fourier-Transform infrared spectroscopy (FTIR). Analysis of nonisothermal DSC data yielded a value of 220.84 ± 2.73 KJ/mol and 2.25 ± 0.26 for the activation energy of crystallization (E _a) and the Avrami exponent (n), respectively.     

Phase transitions of SC(NH<Subscript>2</Subscript>)<Subscript>2</Subscript> ferroelectrics in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-based nanoporous matrices

Temperature dependences of the linear permittivity ε' and the third harmonic amplitude γ_3ω of composites prepared by introducing ferroelectrics SC(NH₂)₂ into matrices of porous aluminum oxide Al₂O₃ with pore sizes 60 and 100 nm are determined. It is found that temperature T _c of the ferroelectric phase transition and the temperature T _i of the phase transition from incommensurable phase to the paraphrase increase significantly. The transition shifts increase as pore diameters decrease.