Showing papers in "Bulletin of Materials Science in 2003"

Projector augmented wave method:ab initio molecular dynamics with full wave functions

Abstract: A brief introduction to the projector augmented wave method is given and recent developments are reviewed. The projector augmented wave method is an all-electron method for efficient ab initio molecular dynamics simulations with full wave functions. It extends and combines the traditions of existing augmented wave methods and the pseudopotential approach. Without sacrificing efficiency, the PAW method avoids transferability problems of the pseudopotential approach and it has been valuable to predict properties that depend on the full wave functions.

Band gap determination of Ni-Zn ferrites

Abstract: Nanocomposites of Ni-Zn with copolymer matrix of aniline and formaldehyde in presence of varying concentrations of zinc ions have been studied at room temperature and normal pressure. The energy band gap of these materials are determined by reflection spectra in the wavelength range 400–850 nm by spectrophotometer at room temperature. From the analysis of reflection spectra, nanocomposites of copolymer of aniline and formaldehyde with Ni1-xZnxFe2O4 (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 10) have been found to have direct band gaps ranging from 1.50–1.66 eV.

Development of a fully injectable calcium phosphate cement for orthopedic and dental applications

Abstract: A study on the development of a fully injectable calcium phosphate cement for orthopedic and dental applications is presented. The paper describes its characteristic properties including results of biocompatibility studies.

Impedance spectroscopy study of polycrystalline Bi6Fe2Ti3O18

Abstract: The electrical properties of polycrystalline Bi6Fe2Ti3O18 are investigated by impedance spectroscopy in the temperature range 30–550°C. The imaginary part of impedance as a function of frequency shows Debye like relaxation. Impedance data are presented in the Nyquist plot which is used to identify an equivalent circuit and the fundamental circuit parameters are determined at different temperatures. The grain and grain-boundary contributions are estimated. The results of bulk a.c. conductivity as a function of temperature and frequency are presented. The activation energies for the a.c. conductivity are calculated. The polaron hopping frequencies are estimated from the a.c. conductivity data.

Electrochemical synthesis and characterization of chloride doped polyaniline

Abstract: Chloride doped polyaniline conducting polymer films have been prepared in a protic acid medium (HCl) by potentiodynamic method in an electrochemical cell and studied by cyclic voltammetry and FTIR techniques. The FTIR spectra confirmed Cl- ion doping in the polymers. The polymerization rate was found to increase with increasing concentration of aniline monomer. But the films obtained at high monomer concentration were rough having a nonuniform flaky polyaniline distribution. Results showed that the polymerization rate did not increase beyond a critical HCl concentration. Cyclic voltammetry suggested that, the oxidation-reduction current increased with an increase in scan rate and that the undoped polyaniline films were not hygroscopic whereas chloride doped polyaniline films were found to be highly hygroscopic.

Heat-deproteinated xenogeneic bone from slaughterhouse waste: Physico-chemical properties

Abstract: Xenogeneic bone procured from the slaughterhouse waste was deproteinated by heat treatment method intended for use as a bone substitute. The effect of heat treatment was investigated by thermal ana - lysis and by physico -chemical methods such as X -ray powder diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. The heat treatment temperatures for the bovine bone samples were pre - determined by thermogravime tric (TG) analysis. The XRD results revealed that the process of heat treatment promoted the crystallinity of bone samples, particularly at 700 and 900°C. There was no secondary phase transformation detected for heat-deproteinated bone except the presence of the hydroxyapatite (HA) phase, which indicated its phase purity even at a higher t emperature. The FTIR spectra of raw bone and bone heated at 300°C indicated the presence of organic macromolecules whereas these disappeared in the samples heated at 500, 700 and 900°C, which suggested the removal of antigenic organic matters around 500°C. The same results were also confirmed quantitatively by calculating the amount of collagen using hydroxyproline esti - mation. There was no significant change in the TG-thermogram of bone heated at 500, 700 and 900°C, which indicated their thermal stability. These findings implied that the heat treated bone at 500°C had properties similar to carbonated HA with low crystallinity, while 700 and 900°C samples had the same with higher crystallinity. As low temperature treatment does not alter morphological and structural properties, we propose that the 500°C heat treated xenogeneic bone may act as an excellent osteogenic bone substitute.

Conductivity behaviour of polymer gel electrolytes: Role of polymer

Abstract: Polymer is an important constituent of polymer gel electrolytes along with salt and solvent. The salt provides ions for conduction and the solvent helps in the dissolution of the salt and also provides the medium for ion conduction. Although the polymer added provides mechanical stability to the electrolytes yet its effect on the conductivity behaviour of gel electrolytes as well as the interaction of polymer with salt and solvent has not been conclusively established. The conductivity of lithium ion conducting polymer gel electrolytes decreases with the addition of polymer whereas in the case of proton conducting polymer gel electrolytes an increase in conductivity has been observed with polymer addition. This has been explained to be due to the role of polymer in increasing viscosity and carrier concentration in these gel electrolytes.

Morphology and conductivity studies of a new solid polymer electrolyte: (PEG)xLiClO4

Abstract: A new solid polymer electrolyte, (PEG)xLiClO4, consisting of poly(ethylene)glycol of molecular weight 2000 and LiClO4 was prepared and characterized using XRD, IR, SEM, DSC, NMR and impedance spectroscopy techniques. XRD and IR results show the formation of the polymer-salt complex. The samples with higher salt concentration are softer, less opaque and less smooth compared to the low salt concentration samples. DSC studies show an increase in the glass transition temperature and a decrease in the degree of crystallinity with increase in the salt concentration. Melting temperature of SPEs is lower than the pure PEG 2000. Room temperature 1H and 7Li NMR studies were also carried out for the (PEG)xLiClO4 system. The 1H linewidth decreases as salt concentration increases in a similar way to the decrease in the crystalline fraction and reaches a minimum at around x = 46 and then increases. 7Li linewidth was found to decrease first and then to slightly increase after reaching a minimum at x = 46 signifying the highest mobility of Li ions for this composition. Room temperature conductivity first increases with salt concentration and reaches a maximum value $(\sigma = 7.3 x 10^-^7 S/cm)$ at x = 46 and subsequently decreases. The temperature dependence of the conductivity can be fitted to the Arrhenius and the VTF equations in different temperature ranges. The ionic conductivity reaches a high value of ~ $10^-^4$ S/cm close to the melting temperature.

Synthesis, characterization and low frequency a.c. conduction of polyaniline/fly ash composites

Abstract: In situ polymerization of aniline was carried out in the presence of fly ash (FA) to synthesize polyaniline/ fly ash (PANI/FA) composites. The PANI/FA composites have been synthesized with various compositions (15, 20, 30 and 40 wt%) of FA in PANI. The composites, thus synthesized have been characterized by infrared spectroscopy and X-ray diffraction. The morphology of these samples was studied by scanning electron microscopy. Further the a.c. conductivity of these composites have been investigated in the frequency range 102–106 Hz. The presence of polarons and bipolarons are made responsible for frequency dependence of a.c. conductivity in these composites. The Cole-Cole plots indicate clear shift in the distribution of relaxation times as the wt% of FA in PANI changes. These composites show almost symmetric semicircles of Cole-Cole plots indicating the Debye-type relaxation in their polarization response.

Dielectric properties of Na1-xKxNbO3 in orthorhombic phase

Abstract: Pellets of ceramic Na1−xKxNbO3 (x = 0, 0.2 and 0.5), were prepared by conventional solid-state reaction method. Prepared samples were characterized using XRD and SEM. The frequency and temperature variation of dielectric constant, loss tangent and dielectric conductivity of prepared samples were measured in the frequency range from 10 KHz-1 MHz, and in the temperature range from 50–250°C for x = 0.2 and 0.5, and between 50 and 480°C for x = 0 compositions. It was observed that the dielectric constant and loss tangent decrease, and conductivity increases with increasing frequency. Near the transition temperature the material shows anomalous behaviour for the observed properties, and the peaks of dielectric constant and loss tangent were observed shifting towards lower temperature with increasing frequency.

Dielectric, electrical and infrared studies of γ-Fe2O3 prepared by combustion method

Abstract: This paper reports the electrical and spectroscopic investigation of the gamma ferrite synthesized through combustion route. The electrical study and dielectric behaviour showed a typical ferrite nature for the samples. The γ → α transition is observed from the electrical conductivity data. Infrared spectral study showed the transition of a typical ferrite. The effect of the presence of α-impurities in γ-Fe2O3 is also explained here.

Aging of trivalent metal hydroxide/oxide gels in divalent metal salt solutions: Mechanism of formation of layered double hydroxides (LDHs)

Abstract: While the aging of freshly precipitated Al(OH)3 gels in solutions of Mg and Ni salts leads to LDH formation at high (> 12) pH, aging of ‘Fe(OH)3“ leads to LDH formation in Mg salt solutions but not in Ni salt3’ gels do not form LDHs on aging in any of the divalent metal salts. In general, conditions that promote the redissolution of the trivalent hydroxide also promote LDH formation showing that oxoanionic species such as AlO-2 have a role in LDH formation.

Third-generation muffin—tin orbitals

Abstract: By the example of sp3-bonded semiconductors, we illustrate what 3rd-generation muffin-tin orbitals (MTOs) are. We demonstrate that they can be downfolded to smaller and smaller basis sets: sp3d10,sp3, and bond orbitals. For isolated bands, it is possible to generate Wannier functions a priori. Also for bands, which overlap other bands, Wannier-like MTOs can be generated a priori. Hence, MTOs have a unique capability for providing chemical understanding.

Space charge limited conduction in CdSe thin films

Abstract: The current (I)-voltage (V) characteristics of thermally evaporated CdSe thin films having thickness in the range 850–3000 A and deposited within the substrate temperature of 303–573 K show nearly linear dependence at low voltage and afterwards a non-linear behaviour at higher voltage range. A detailed study ofI-V curves in dark and under illumination clearly reveals the mechanism as ohmic at low voltage and that of trap limited space charge limited conduction (SCLC) at higher voltage. The transition voltage (Vt) from ohmic to SCLC is found to be quite independent of ambient temperature as well as intensity of illumination. SCLC is explained on the basis of the exponential trap distribution in CdSe films. Trap depths estimated from the lnI vs 103/T plots are found to be within 0.60-0.37 eV. Using the relevant SCLC theory, the carrier concentration, n0, total trap concentration, Nt, and the ratio of free charge to trapped charge, θ, have been calculated and correlated with ambient temperature and intensity of illumination.

Tribological behaviour of conventional Al-Sn and equivalent Al-Pb alloys under lubrication

Abstract: Two compositions of conventional aluminium base alloys were selected and equal amounts of tin and lead as a soft phase were incorporated separately. Impeller mixing and chill casting technique were employed for the preparation of the alloys. Mechanical properties of as cast alloys were evaluated at room temperature. Frictional behaviour of the alloys was studied in detail under lubrication while creating different frictional states by imposing 5–60 kg of normal load on the bearing (bush) mating surface. It was found that aluminium tin and leaded aluminium alloys slightly differ in mechanical properties. Frictional states created during sliding against steel shaft (hardness 55–60 Rc) under oil lubrication were not much different. Leaded aluminium alloy bushes show marginally lower friction than the conventional ones.

Thermogravimetry-evolved gas analysis-mass spectrometry system for materials research

Abstract: Thermal analysis is a widely used analytical technique for materials research. However, thermal analysis with simultaneous evolved gas analysis describes the thermal event more precisely and completely. Among various gas analytical techniques, mass spectrometry has many advantages. Hence, an ultra high vacuum (UHV) compatible mass spectrometry based evolved gas analysis (EGA-MS) system has been developed. This system consists of a measurement chamber housing a mass spectrometer, spinning rotor gauge and vacuum gauges coupled to a high vacuum, high temperature reaction chamber. A commercial thermogravimetric analyser (TGA: TG + DTA) is interfaced to it. Additional mass flow based gas/vapour delivery system and calibration gas inlets have been added to make it a versatile TGA-EGA-MS facility. This system which gives complete information on weight change, heat change, nature and content of evolved gases is being used for (i) temperature programmed decomposition (TPD), (ii) synthesis of nanocrystalline materials, (iii) gas-solid interactions and (iv) analysis of gas mixtures. The TPD of various inorganic oxyanion solids are studied and reaction intermediates/products are analysed off-line. The dynamic operating conditions are found to yield nanocrystalline products in many cases. This paper essentially describes design features involved in coupling the existing EGA-MS system to TGA, associated fluid handling systems, the system calibration procedures and results on temperature programmed decomposition. In addition, synthesis of a few nanocrystalline oxides by vacuum thermal decomposition, gas analysis and potential use of this facility as controlled atmosphere exposure facility for studying gas-solid interactions are also described.

A study of phase separation in ternary alloys

Abstract: We have studied the evolution of microstructure when a disordered ternary alloy is quenched into a ternary miscibility gap. We have used computer simulations based on multicomponent Cahn-Hilliard (CH) equations for c A and cB, the compositions (in mole fraction) of A and B, respectively. In this work, we present our results on the effect of relative interfacial energies on the temporal evolution of morphologies during spinodal phase separation of an alloy with average composition, cA = 1/4, cB = 1/4 and cc = 1/2. Interfacial energies between the ‘A’ rich, ‘B’ rich and ‘C’ rich phases are varied by changing the gradient energy coefficients. The phases associated with a higher interfacial energy are found to be more rounded than those with lower energy. Further, the kinetic paths (i.e. the history of A-rich, B-rich and C-rich regions in the microstructure) are also affected significantly by the relative interfacial energies of the three phases.

Structural and magnetic properties of Co1+ySnyFe2-2y-xCrxO4 ferrite system

Abstract: The samples of the series Co1+ySnyFe2- 2y- xCrxO4 ferrites with x = 0.0, 0.1, 0.2, 0.3, 0.4, 0.5 and y = 0.05, were prepared by the usual double sintering ceramic technique. The single- phase spinel structure of the samples was confirmed by using X- ray diffractometry technique. The lattice parameter ’a’ with an accuracy of ± 0.002 A were determined using Bragg peaks of XRD pattern. The lattice parameter ’a’ decreases with concentration, x, which is due to the difference in the ionic radii of Cr3+ and Fe3+ ions. The X- ray intensity calculations were carried out in order to determine the possible cation distribution amongst tetrahedral (A) and octahedral [B] sites. The X- ray intensity calculations show Cr3+ ions occupying B site. The saturation magnetization, σs, and magneton number, nB (the saturation magnetization per formula unit), measured at 300 K determined from high field hysteresis loop technique decrease with increase in concentration, x, suggesting a decrease in ferrimagnetic behaviour. Thermal variation of low field a.c. susceptibility measurements from room temperature to about 800 K exhibits almost normal ferrimagnetic behaviour and the Curie temperature, TC determined from a.c. susceptibility data decreases with increase in x.

Irradiation induced grain growth and surface emission enhancement of chemically tailored ZnS : Mn/PVOH nanoparticles by Cl+9 ion impact

Abstract: Manganese doped zinc sulfide nanoparticles are fabricated on polyvinyl alcohol dielectric matrix. They are bombarded with energetic chlorine ions (100 MeV). The size of the crystallites is found to increase with ion fluence due to melting led grain growth under ion irradiation. The increased size as a result of grain growth has been observed both in the optical absorption spectra in terms of redshift and in electron microscopic images. The photoluminescence (PL) study was carried out by band to band excitation (λex = 220 nm) upon ZnS : Mn, which results into two emission peaks corresponding to surface states and Mn+2 emission, respectively. The ion fluence for irradiation experiment so chosen were 1 × 1011, 5 × 1011, 5 × 1012 and 1013 Cl/cm2.

The promise of fuel cell-based automobiles

Abstract: Fuel cell-based automobiles have gained attention in the last few years due to growing public concern about urban air pollution and consequent environmental problems. From an analysis of the power and energy requirements of a modern car, it is estimated that a base sustainable power of ca. 50 kW supplemented with short bursts up to 80 kW will suffice in most driving requirements. The energy demand depends greatly on driving characteristics but under normal usage is expected to be 200 Wh/km. The advantages and disadvantages of candidate fuel-cell systems and various fuels are considered together with the issue of whether the fuel should be converted directly in the fuel cell or should be reformed to hydrogen onboard the vehicle. For fuel cell vehicles to compete successfully with conventional internal-combustion engine vehicles, it appears that direct conversion fuel cells using probably hydrogen, but possibly methanol, are the only realistic contenders for road transportation applications. Among the available fuel cell technologies, polymer-electrolyte fuel cells directly fueled with hydrogen appear to be the best option for powering fuel cell vehicles as there is every prospect that these will exceed the performance of the internal-combustion engine vehicles but for their first cost. A target cost of $ 50/kW would be mandatory to make polymer-electrolyte fuel cells competitive with the internal combustion engines and can only be achieved with design changes that would substantially reduce the quantity of materials used. At present, prominent car manufacturers are deploying important research and development efforts to develop fuel cell vehicles and are projecting to start production by 2005.

Deposition of TiN/CrN hard superlattices by reactive d.c. magnetron sputtering

Abstract: Multilayer superlattice coatings of TiN/CrN were deposited on silicon substrates using a reactive d.c. magnetron sputtering process. Superlattice period, also known as modulation wavelength (?), was controlled by controlling the dwell time of the substrate underneath Ti and Cr targets. X-ray diffraction (XRD), nanoindentation and atomic force microscopy (AFM) were used to characterize the films. The XRD data showed 1st and 2nd order satellite reflections along the principal reflection for films having 132 A? ? ? ? 84 A?, thus confirming the formation of superlattice. The multilayer coatings exhibited hardness (H) as high as 3200 kg/mm2, which is 2 times the rule-of-mixtures value (i.e. HTiN = 2200 kg/mm2 and HCrN = 1000 kg/mm2). Detailed investigations on the effect of various process parameters indicated that hardness of the superlattice coatings was affected not only by modulation wavelength but also by nitrogen partial pressure and ion bombardment during deposition.

Optical absorption and fluorescent behaviour of titanium ions in silicate glasses

Abstract: Titanium in normal melting conditions in air atmosphere present as Ti4+ ion in basic silicate glasses exhibited an ultra-violet cut-off in silicate glasses, viz soda-magnesia-silica, soda-magnesia-lime-silica and soda-lime-silica glasses This indicates that Ti4+ ion can be a good replacement for Ce4+ ion in producing UV-absorbing silicate glasses for commercial applications The wavelength maxima at which the infinite absorption takes place in glasses was found to be around 310 nm against Ti-free blank glass in UV-region The mechanism of electronic transition from O2- ligands to Ti4+ ion was suggested as L→ M charge transfer The low energy tails of the ultra-violet cut-off were found to obey Urbach’s rule in the optical range 360–500 nm The fluorescence spectra of these glasses were also studied and based on the radiative fluorescent properties it was suggested that the soda-lime-silica glass containing Ti4+ ion with greater emission cross-section would emit a better fluorescence than the corresponding soda-magnesia-lime-silica and sodamagnesia-silica glasses The shift of emission wavelengths maxima towards longer wavelength in titania introduced silicate glasses was observed on replacement of MgO by CaO which may be attributed due to an increase in basicity of the glass system

Crystallization study of Te-Bi-Se glasses

Abstract: Crystallization studies are carried out under non -isothermal conditions with samples heated at several uniform rates. The dependence of the glass transition te mperature (Tg), the crystalline temperature (Tc) and the peak temperature of crystallization ( Tp) on the composition and heating rate (β) has been studied. For a memory/switching material, the thermal stability and ease of glass formation are of crucial impo rtance. The glass transition temperature, Tg, increases slightly with the vari ation of Bi content. From the heating rate dependence of Tg, the activation energy for glass transition ( Et) has been evaluated. The results are discussed on the basis of Kis singer's approach and are interpreted using the chemically ordered network model (CONM).

Carbonization and demineralization of coals: A study by means of FT-IR spectroscopy

Abstract: Coal basically consists of two parts—a crystalline, inorganic part, and an amorphous, organic part. Based on this, we intended to study the changes that occurred on the composition and on the chemical structure of coals after carbonization at 1000 or 900° C and demineralization treatments with hydrochloric and hydrofluoric acids. For this, four coals of different categories (or levels) were chosen: semianthracite (A-O) and high volatile bituminous coal (B-O), which are high level coals, and lignite (Li-O) and leonardite (Le-O), these being low level coals. The coals were first analysed in terms of their proximate and elemental compositions and then carbonized and demineralized. Also, the starting coals and the prepared samples were examined by infrared spectroscopy. In addition, a study of the optimization of the application of this technique for only A-O was carried out. For A-O and B-O, the spectra recorded intense absorption bands that are ascribable to vibration modes in mineral components as quartz and aluminosilicates, such as kaolinite. For Li-O and Le-O, the spectra displayed some other bands as well, also quite intense, which have been assigned to bond vibrations in functional groups and structures of their organic part. The carbonization of the coals resulted in significant changes in their inorganic part as the content of quartz increased and the content of aluminosilicates decreased. In addition, the thermal decomposition of mineral carbonates occurred. The carbonization greatly affects the organic part of the coals, especially in Li-O and Le-O, as most functional groups and structures are not thermally stable under heating conditions. With regard to demineralization, HF is a more effective agent than HCl, achieving products with higher organic content. The mass losses are higher in Li-O and Le-O than in A-O and B-O. So, the infrared spectroscopy allows the analysis of both inorganic and organic parts of the coals and of their carbonization and demineralization products. These processes facilitate subsequent analysis of the inorganic and organic parts of coals by infrared spectroscopy. In the application of this technique, both the coal: KBr ratio and the thickness for the disks should be controlled, owing to the influence on the infrared absorption.

Linear and nonlinear optical properties of borate crystals as calculated from the first principles

Abstract: With the development of the state-of-the-art band calculation scheme and massively parallel processing in the high performance computing, we are now able to calculate all important physical properties, including (i) the nonlinear susceptibility; (ii) the multiphoton absorption rate; (iii) the birefringence; and (iv) the energy gap, from the first principles for complex practical nonlinear optical crystals, such as the borate crystal series, with an accuracy acceptable for materials development/design, and answer the questions often raised by the material scientists.

Charge dynamics in conducting polyaniline-metal oxalate composites

Abstract: Polyaniline (Pani) and its metal oxalate composites (∼10 wt.%) of trivalent metal ions of Cr, Fe, Mn, Co and Al were synthesized by chemical oxidative polymerization technique with potassium perdisulphate oxidant in aqueous sulphuric acid medium. These materials were characterized by UV-VIS and EPR spectral techniques. Their d.c. electrical conductivities at room temperature and also as a function of temperature (307-453 K) were measured by four- probe technique. Presence of radical cation/polaron transition was indicated by UV- VIS absorption peak and EPR signals. Further, a close correlation existed between the conductivities and EPR parameters such as line width and peak ratio, which demonstrated that both mobile and fixed spins are involved in these composites. The dependence of conductivity on temperature, when analysed graphically by VRH, GB and TC mechanisms, pointed out that VRH is the predominant charge transport mechanism in these materials.

Synthesis and characterization of biocompatible hydroxyapatite coated ferrite

Abstract: Ferrite particles coated with biocompatible phases can be used for hyperthermia treatment of cancer. We have synthesized substituted calcium hexaferrite, which is not stable on its own but is stabilized with small substitution of La. Hexaferrite of chemical composition (CaO)0.75(La203)0.20(Fe2O3)6 was prepared using citrate gel method. Hydroxyapatite was prepared by precipitating it from aqueous solution of Ca(NO3)2 and (NH4)2HPO4 maintaining pH above 11. Four different methods were used for coating of hydroxyapatite on ferrite particles. SEM with EDX and X-ray diffraction analysis shows clear evidence of coating of hydroxyapatite on ferrite particles. These coated ferrite particles exhibited coercive field up to 2 kOe, which could be made useful for hysteresis heating in hyperthermia. Studies by culturing BHK-21 cells and WBC over the samples show evidence of biocompatibility. SEM micrographs and cell counts give clear indication of cell growth on the surface of the sample. Finally coated ferrite particle was implanted in Kasaulli mouse to test its biocompatibility. The magnetic properties and biocompatibility studies show that these hydroxyapatite coated ferrites could be useful for hyperthermia.

Corrosion of reinforcement induced by environment containing chloride and carbon dioxide

Abstract: Reinforced concrete structures during their exploitation may be exposed to the common action of carbonation and chlorides causing corrosion of steel reinforcement. Therefore, the related data seem to be interesting and important when the evaluation of the service life of the structures is the object of interest. This fact was a motivation for the present experimental study on the sequence of action of chloride solutions and carbonation of the embedding concrete. The results obtained show that carbonation of concrete foregoing the action of chloride solutions may intensify the process of corrosion of steel reinforcement in comparison to the converse sequence of the action of mentioned media. At the same time the natrium chloride solution has been shown as a more aggressive medium opposite to the calcium and magnesium chloride solutions.

Preparation of microwave dielectric, Sn 0.2 Zr 0.8 TiO 4

Abstract: A simple coprecipitation technique is described for the preparation of tin substituted zirconium titanate ceramic powders.

Preparation and characterization of Eu3+ activated CaSiO3, (CaA)SiO3 [A = Ba or Sr] phosphors

Abstract: Eu3+ activated CaSiO3, (Ca, Ba) SiO3 and (Ca, Sr) SiO3 have been prepared by sol-gel technique. Residual solvent and organic contents in the gel were removed by firing at 100°C for 3–4 h at 300 and 600°C for 2 h. Small exothermic shoulder around 850 to 875°C, as observed in DTA curve, corresponds to crystallization temperature of the doped calcium silicate. Influence of firing temperature on the luminescence of Eu3+ shows the maximum emission intensity in gel fired at 850°C. Photoluminescence emission peak is observed at 614 nm due to5D0 →7F2 transition of Eu3+ ion in (Ca, Ba) SiO3 and (Ca, Sr) SiO3 phosphors, when excited by 254 nm. The (Ca, Ba) SiO3 material is proposed as an efficient red phosphor.