Synthesis, structural characterization and ferroelectric properties of Pb(0.76)Ca(0.24)TiO(3) nanotubes

A capillary-enforced template-based method has been applied to fabricate Pb(0.76)Ca(0.24)TiO(3) (PCT24) nanotubes via filling PCT24 precursor solution, prepared by modified sol-gel method, into nanochannels of anodic aluminum oxide templates. The morphology and structure of as-prepared PCT24 were examined by scanning electron microscopy, transmission electron microscopy (TEM) and X-ray diffraction techniques. The obtained PCT24 nanotubes with diameter of similar to 200 nm and wall thickness of similar to 20 nm exhibited a tetragonal perovskite structure. High resolution TEM (HRTEM) analysis confirmed that as-obtained PCT24 nanotubes made up of nanoparticles (5-8 nm) which were randomly aligned in the nanotubes. Formation of some solid crystalline PCT24 nanorods, Y-junctions and multi-branches were observed. Interconnections in the pores of template are responsible for the growth of Y-junctions and multi-branches. The possible formation mechanism of PCT24 nanotubes/nanorods was discussed. Ferroelectric hysteresis loops of PCT24 nanotube arrays were measured, showing a room temperature ferroelectric characteristic of as-prepared PCT24 nanotubes. (C) 2011 Elsevier B.V. All rights reserved.

Synthesis and nonlinear optical properties of Lead Telluride nanorods

Lead Telluride (PbTe) nanorods have been uniformly grown on silicon substrates, using the thermal evaporation technique under high vacuum conditions. The structural and morphological studies are done using X-ray diffraction and scanning electron microscopy. Optical nonlinearity studies using the open aperture z-scan employing 5 ns and 100 fs laser pulses reveal a three-photon type absorption. For nanosecond excitation the nonlinear absorption coefficients (gamma) are in the order of 10(-22) m(3) W-2 and for femtosecond excitation it is in the order of 10(-29) m(3) W-2. The role of free carriers and excitons in causing the nonlinearity in both excitation time domains is discussed. Results indicate that PbTe nanorods are good optical limiters with potential device applications. (C) 2011 Elsevier B.V. All rights reserved.

Compositionally modulated Pb(Mg1/3Nb2/3)O-3-PbTiO3 relaxor thin films deposited by pulsed excimer laser ablation technique

Thin films of (1-x)Pb(Mg1/3Nb2/3)O-3 - xPbTiO(3) (x = 0.1 to 0.3)(PMN-PT) were deposited on the platinum coated silicon substrate by pulsed excimer laser ablation technique. A template layer of LaSr0.5Co0.5O3 (LSCO) was deposited on platinum substrate prior to the deposition of PMN-PT thin films. The composition and the structure of the films were modulated via proper variation of the deposition parameter such as substrate temperature, laser fluence and thickness of the template layers. We observed the impact of the thickness of LSCO template layer on the orientation of the films. A room temperature dielectric constant varying from 2000 to 4500 was noted for different composition of the films. The dielectric properties of the films were studied over the frequency range of 100 Hz - 100 kHz over a wide range of temperatures. The films exhibited the relaxor- type behavior that was characterized by the frequency dispersion of the temperature of dielectric constant maxima (T-m) and also diffuse phase transition. C1 Indian Inst Sci, Mat Res Ctr, Bangalore, Karnataka 560012 India.

Compositionally and structurally modulated Pb(Mg1/3Nb2/3)O3-PbTiO3 relaxor thin films for microactuator application

Thin films of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3(x = 0.1 to 0.3) (PMN-PT) were successfully grown on the platinum coated silicon substrate by pulsed excimer laser ablation technique. A thin template layer of LaSr0.5Co0.5O3 (LSCO) was deposited on platinum substrate prior to the deposition of PMN-PT thin films. The composition and the structure of the films were modulated via proper variation of the deposition parameter such as substrate temperature, laser fluence and thickness of the template layers. We observed the impact of the thickness of LSCO template layer on the orientation of the films. The crystallographic structure and compositional variation were confirmed with x-ray diffraction and energy diffraction x-ray (EDX) analysis. A room temperature dielectric constant varying from 2000 to 4500 was noted for different composition of the films. The dielectric properties of the films were studied over the frequency range of 100 Hz - 100 kHz over a wide range of temperatures. The films exhibited the relaxor-type behavior that was characterized by the frequency dispersion of the temperature of dielectric constant maxima (Tm) and also diffuse phase transition. This relaxor nature in PMN-PT thin films was attributed to freezing of the dipole moment, which takes place below a certain temperature. This phenomenon was found to be very similar to spin glass system, where spins are observed to freeze after certain temperature.

Nano Al2O3-Pb AND SiO2-Pb cermets by sol-gel technique and the phase transformation study of the embedded Pb particles

Sol-gel processing followed by H2 reduction is used to produce dispersions of nanosized Pb in amorphous SiO2 and ultrafine γ Al2O3 matrices. A depression of 3–5K in Pb melting point is reported. The size and shape of these metastable particles in molten and solid state are discussed in the light of the experimental observations and expectations from the intersection group theory for equilibrium shape.

Chemically functionalized glassy carbon spheres: a new covalent bulk modified composite electrode for the simultaneous determination of lead and cadmium

A new type of covalent bulk modified glassy carbon composite electrode has been fabricated and utilized in the simultaneous determination of lead and cadmium ions in aqueous medium. The covalent bulk modification was achieved by the chemical reduction of 2-hydroxybenzoic acid diazonium tetrafluroborate in the presence of hypophosphorous acid as a chemical reducing agent. The covalent attachment of the modifier molecule was examined by studying Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and the surface morphology was examined by scanning electron microscopy images. The electrochemistry of modified glassy carbon spheres was studied by its cyclic voltammetry to decipher the complexing ability of the modifier molecules towards Pb2+ and Cd2+ ions. The developed sensor showed a linear response in the concentration range 1-10 mu M with a detection limit of 0.18 and 0.20 mu M for lead and cadmium, respectively. The applicability of the proposed sensor has been checked by measuring the lead and cadmium levels quantitatively from sewage water and battery effluent samples.

Lead ion sensor with electrodes modified by imidazole-functionalized polyaniline

Glassy carbon electrodes (GCE) and carbon paste electrodes (CPE) were modified with imidazole functionalized polyaniline with the aim to develop a sensor for lead (II) in both acidic and basic aqueous solution. The electrodes were characterized by cyclic voltammetry and differential pulse adsorptive stripping voltammetry. The limit of detections obtained with glassy carbon electrode and carbon paste electrode are 20 ng mL(-1) and 2 ng mL(-1) of lead ion, respectively. An interference study was carried out with Cd(II), As(III), Hg(II) and Co(II) ions. Cd(II) ions interfere significantly (peak overlap) and As(III) has a depressing effect on the lead signal. The influence of pH was investigated indicating that bare and modified GCE and CPE show optimum response at pH 4.0 +/- 0.05.

Enhanced J-protein interaction and compromised protein stability of mtHsp70 variants lead to mitochondrial dysfunction in Parkinsons disease

Parkinsons disease (PD) is the second most prevalent progressive neurological disorder commonly associated with impaired mitochondrial function in dopaminergic neurons. Although familial PD is multifactorial in nature, a recent genetic screen involving PD patients identified two mitochondrial Hsp70 variants (P509S and R126W) that are suggested in PD pathogenesis. However, molecular mechanisms underlying how mtHsp70 PD variants are centrally involved in PD progression is totally elusive. In this article, we provide mechanistic insights into the mitochondrial dysfunction associated with human mtHsp70 PD variants. Biochemically, the R126W variant showed severely compromised protein stability and was found highly susceptible to aggregation at physiological conditions. Strikingly, on the other hand, the P509S variant exhibits significantly enhanced interaction with J-protein cochaperones involved in folding and import machinery, thus altering the overall regulation of chaperone-mediated folding cycle and protein homeostasis. To assess the impact of mtHsp70 PD mutations at the cellular level, we developed yeast as a model system by making analogous mutations in Ssc1 ortholog. Interestingly, PD mutations in yeast (R103W and P486S) exhibit multiple in vivo phenotypes, which are associated with omitochondrial dysfunction', including compromised growth, impairment in protein translocation, reduced functional mitochondrial mass, mitochondrial DNA loss, respiratory incompetency and increased susceptibility to oxidative stress. In addition to that, R103W protein is prone to aggregate in vivo due to reduced stability, whereas P486S showed enhanced interaction with J-proteins, thus remarkably recapitulating the cellular defects that are observed in human PD variants. Taken together, our findings provide evidence in favor of direct involvement of mtHsp70 as a susceptibility factor in PD.

Modeling of Ascending/Descending Velocity of Metal Droplet Emulsified in Pb-Salt System

Metal-slag emulsion is an important process to enhance the reaction rate between the two phases; thus, it improves the heat and mass transfer of the process significantly. Various experimental studies have been carried out, and some system specific relations have been proposed by various investigators. A unified, theoretical study is lacking to model this complex phenomenon. Therefore, two simple models based on fundamental laws for metal droplet velocity (both ascending and descending) and bubble velocity, as well as its position at any instant of time, have been proposed. Analytical solutions have been obtained for the developed equations. Analytical solutions have been verified for the droplet velocity, traveling time, and size distribution in slag phase by performing high-temperature experiments in a Pb-salt system and comparing the obtained data with theory. The proposed model has also been verified with published experimental data for various liquid systems with a wide range of physical properties. A good agreement has been found between the analytical solution and the experimental and published data in all cases.

Synthesis, luminescence and EPR studies on CaSiO 3: Pb, Mn-nano phosphors synthesized by the solution combustion method

Nano-ceramic phosphor CaSiO 3 doped with Pb and Mn was synthesized by the low temperature solution combustion method. The materials were characterized by Powder X-Ray Diffraction (XRD), Thermo-gravimetric and Differential Thermal Analysis (TG-DTA), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). The Electron Paramagnetic Resonance (EPR) spectrum of the investigated sample exhibits a broad resonance signal centered at g=1.994. The number of spins participating in resonance (N) and its paramagnetic susceptibility (�) have been evaluated. Photoluminescence of doped CaSiO 3 was investigated when excited by UV radiation of 256 nm. The phosphor exhibits an emission peak at 353 nm in the UV range due to Pb 2+. Further, a broad emission peak in the visible range 550-625 nm can be attributed to 4T 1� 6A 1 transition of Mn 2+ ions. The investigation reveals that doping perovskite nano-ceramics with transition metal ions leads to excellent phosphor materials for potential applications. © 2012 Elsevier Ltd and Techna Group S.r.l.

Synthesis, characterisation, and DC conductivity of polyaniline-lead oxide composites

The polyaniline-PbO composites of various mass fractions were prepared by in situ polymerisation. The prepared samples were characterised by FTIR, and the dominant peaks confirmed the formation of polyaniline-PbO composites. The SEM study shows a granular agglomerated morphology, and increases with an increase in the lead oxide mass % in polyaniline. Direct current (DC) conductivity (sigma (DC)) was studied as a function of temperature (T). From these studies, it was found that conductivity increased at higher temperatures due to the polarons hopping from one localised state to another. DSC studies reveal, the decrease in peak temperature from 273A degrees C (pure PANI) to 169.2A degrees C, 193.5A degrees C, 218.4A degrees C, 235.2A degrees C, and 224.2A degrees C, respectively for the various mass fractions (10 %, 30 %, 20 %, 40 %, and 50 %) of polyaniline-PbO composites.

Thermoelectric properties of PbTe with encapsulated bismuth secondary phase

Lead Telluride (PbTe) with bismuth secondary phase embedded in the bulk has been prepared by matrix encapsulation technique. X-Ray Diffraction results indicated crystalline PbTe, while Rietveld analysis showed that Bi did not substitute at either Pb or Te site, which was further confirmed by Raman and X-Ray Photoelectron Spectroscopy. Scanning Electron Microscopy showed the expected presence of a secondary phase, while Energy Dispersive Spectroscopy results showed a slight deficiency of tellurium in the PbTe matrix, which might have occurred during synthesis due to higher vapor pressure of Te. Transmission Electron Microscopy results did not show any nanometer sized Bi phase. Seebeck coefficient (S) and electrical conductivity (sigma) were measured from room temperature to 725 K. A decrease in S and sigma with increasing Bi content showed an increased scattering of electrons from PbTe-Bi interfaces, along with a possible electron acceptor role of Bi secondary phase. An overall decrease in the power factor was thus observed. Thermal conductivity, measured from 400K to 725K, was smaller at starting temperature with increasing Bi concentration, and almost comparable to that of PbTe at higher temperatures, indicating a more important role of electrons as compared to phonons at PbTe-Bi interfaces. Still, a reasonable zT of 0.8 at 725K was achieved for undoped PbTe, but no improvement was found for bismuth added samples with micrometer inclusions. (C) 2013 American Institute of Physics. http://dx.doi.org/10.1063/1.4796148]

A new approach for understanding ion transport in glasses; example of complex alkali diborate glasses containing lead, bismuth and tellurium oxides

Mechanism of ion transport in glasses continues to be incompletely understood. Several of the theoretical models in vogue fail to rationalize conductivity behaviour when d.c. and a.c. measurements are considered together. While they seem to involve the presence of at least two components in d.c. activation energy, experiments fail to reveal that feature. Further, only minor importance is given to the influence of structure of the glass on the ionic conductivity behaviour. In this paper, we have examined several general aspects of ion transport taking the example of ionically conducting glasses in pseudo binary, yNa(2)B(4)O(7)center dot(1-y) M (a) O (b) (with y = 0 center dot 25-0 center dot 79 and M (a) O (b) = PbO, TeO2 and Bi2O3) system of glasses which have also been recently characterized. Ion transport in them has been studied in detail. We have proposed that non-bridging oxygen (NBO) participation is crucial to the understanding of the observed conductivity behaviour. NBO-BO switching is projected as the first important step in ion transport and alkali ion jump is a subsequent event with a characteristically lower barrier which is, therefore, not observed in any study. All important observations in d.c. and a.c. transport in glasses are found consistent with this model.

Fine scale characterization of surface/subsurface and nanosized debris particles on worn Cu-10 % Pb nanocomposites

The identification of the damage mechanisms involved in the wear process demands the finer scale characterization of the surface, as well as the subsurface region of the wear scar region, and to this end, this article discusses the results obtained with Cu-10 wt% Pb-based metallic nanocomposites using a host of characterization techniques, including transmission electron microscopy and ion milling microscopy. Apart from finer scale characterization to understand deformation and cracking during the wear process, X-ray photoelectron spectroscopy analysis of wear debris confirms the occurrence of oxidation of Pb phase to Pb3O4. In order to understand the role of oxides on friction and wear, sliding wear tests in argon were also carried out and such tests did not result in the formation of any tribo-oxides, as confirmed using electron probe microanalysis. Conclusively, oxidative wear is attributed as the dominant wear mechanism in ambient conditions for Cu-10 wt% Pb composite.

Densification kinetics, phase assemblage and hardness of spark plasma sintered Cu-10 wt% TiB2 and Cu-10 wt% TiB2-10 wt% Pb composites

The present work demonstrates the synthesis of Cu-10 wt% TiB2 composites with a theoretical density of more than 90% by tailoring the spark plasma sintering (SPS) conditions in the temperature range of 400-700 degrees C. Interestingly, 10 wt% Pb addition to Cu-10 wt% TiB2 lowers the sinter density and the difference in the densification behavior of the investigated compositions was discussed in reference to the current profile recorded during a SPS cycle. The sintering kinetics and phase assemblage were also discussed in reference to surface melting of the constituents prior to bulk melting temperature, temperature dependent wettability of Pb on Cu, diffusion kinetics of Cu as well as the formation of various oxides. An important result is that a high hardness of around 2 GPa and relative density close to 92% qtheoretical was achieved for the Cu-10 wt% TiB2-10 wt% Pb composite, and such a combination has never been achieved before using any conventional processing route.