Increasing Pb Content Research Articles

Growth of Ultra-Thin PtxPb1-x Electrocatalysts By Surface Limited Redox Replacement and Study of Their Adsorption Properties

The development of inexpensive, active and stable Pt catalysts relevant to fuel cell applications remains a very active area of research. The most promising approaches to improve the performance of Pt catalysts while reducing the total noble metal content include Pt thin-film overlayers1 and Pt-X alloy skin and skeleton structures that comprise a Pt-rich surface supported on a Pt-X alloy2. The confinement of the dimensions to a few atomic layers, coupled with the neighbourhood of Pt to another metal, causes electronic and geometrical effects that substantially alter the catalytic performance and adsorption binding energies. Furthermore, this work is motivated by promising results concerning the catalytic activity of PtxPb1-x alloys for formic acid oxidation3 and the suppression of CO poisoning4. Thus, in this work we have explored the effect of controlling film thickness and Pb content on adsorption and catalytic activity.One of the most successful methods to grow thin film overlayers is known as Surface Limited Redox Replacement (SLRR)5. In this method, a monolayer of underpotentially deposited (UPD) metal is galvanically displaced by Pt. Recently, it was demonstrated that both the UPD step and the redox replacement by more noble ions can be performed in a single electrochemical cell, assisted by Pb UPD6. Recent work has shown the application of Pb UPD to the formation of Pt4Cu overlayers7. However, the application of this method to Pt alloy thin films has not been thoroughly explored.In this work, we explored the SLRR-based deposition of PtxPb1-x alloys in a single solution containing 0.1 M NaClO4, 1 mM Pb(ClO4)2, 1 mM HClO4 and 0.5 mM K2PtCl4. The deposition protocol included (1) Pb UPD on a Au substrate by application of a 1 s pulse at -0.85V vs MSE and (2) a redox replacement reaction under open circuit conditions. The OCP was monitored and interrupted at selected values in the potential region for Pb UPD on Pt. In this way, the Pb content in each layer was controlled. Films of 10 ML in thickness of different composition were grown by repeated deposition cycles.The variation in surface composition with upper limit potential and thickness has been verified by XPS measurements. The coverage of H UPD has been shown to decrease dramatically with Pb content, as shown in Figure 1A. In fact, the estimated Pt active areas obtained from the H UPD charge are much lower than the ones measured by XPS on the same alloys. This observation can possibly be explained by a screening effect of Pb causing an inhibition of H-adsorption. A similar effect has been observed in other Pt bimetallic systems8,9.In this work, we have also examined the CO stripping behaviour on alloys. CO stripping was performed by polarising the electrode at -0.6 V in CO saturated 0.5 M H2SO4solution. Linear sweeps in the CO free solution are presented in Figure 1B.A negative shift of the onset potential for CO stripping and change in peak shape as the Pb content increases can be observed. These changes can be ascribed to an electronic effect from Pb, or a bifunctional effect affecting the onset of OH adsorption10. The charges obtained by integration of the stripping peaks are in quantitative agreement with those obtained by H UPD, indicating the coverage obtained by CO follows the same trend. References 1 R.R. Adzic, J. Zhang et al., Top. Catal. 46, 13 (2007). 2 V. R. Stamenkovic, B. S. Mun et al., J. Am. Chem. Soc. 128, 8813 (2006). 3 S.-M. Hwang, J. E. Bonevich et al., J. Electrochem. Soc. 158, B1019 (2011). 4 N. de-los-Santos-Álvarez, L.R. Alden et al., J. Electroanal. Chem. 626, 14 (2009). 5 S. R. Brankovic, J. X. Wang et al., Surf. Sci. 474, L173 (2001). 6 M. Fayette, Y. Liu et al., Langmuir 27, 5650 (2011). 7 L. Bromberg, M. Fayette et al., Electrocatalysis 4, 24 (2013). 8 Dennis F. van der Vliet, Chao Wang et al., Angew. Chem. Int. Ed. 51, 3139 (2012). 9 H. Schulenburg, J. Durst et al., J. Electroanal. Chem. 642, 52 (2010). 10 H. A. Gasteiger, N. M. Markovic et al., J. Phys. Chem. 98, 617 (1994).

Loading Rate-Dependent Mechanical Properties of Bulk Two-Phase Nanocrystalline Al-Pb Alloys Studied by Nanoindentation

Bulk samples (dia. = 20 mm) of various nanocrystalline (nc) Al-Pb alloys with Pb content varying from 1 to 4 at. pct are fabricated using spark plasma sintering of ball-milled powders. Al matrix in Al-2 at. pct Pb alloy had a grain size of 53 nm, and Pb particle size was 6 ± 2 nm. High angle annular dark-field image obtained in STEM mode of TEM indicates the presence of Pb along the nc Al grain boundaries as well as dispersion of smaller Pb particles in the intra-granular regions. Hardness studies are carried out using microindentation and nanoindentation with load varying over three orders of magnitude (100 − 0.1 g). Microindentation yielded slightly smaller hardness values in comparison to nanoindentation possibly because of indentation size effect. Nevertheless both microindentation and nanoindentation resulted in the same trend of hardness for various nc Al-Pb alloys. Hardness of Al-Pb alloys increased with increase in Pb content up to the additions of 2 at. pct Pb, beyond that the hardness is decreased for higher Pb additions of 3 and 4 pct. The initial hardening behavior is explained based on the Orowan particle strengthening. Strain rate sensitivity (SRS) has increased with increase in Pb content reaching a value of 0.1 for Al-4 at. pct Pb alloy. Activation volumes measured are between 2.84 and 6.15 b 3. Higher SRS and lower activation volume suggest that grain boundary-mediated processes are controlling the deformation characteristics.

An Investigation Into the Role of Lead as a Suppressant for Tin Whisker Growth in Electronics

The effect on Sn electrodeposits of up to 10 wt.% codeposited Pb was investigated. The influence of Pb on cathodic polarization of the electrodeposition process, the microstructural and crystallographic characteristics of as-deposited films, the Sn-Cu intermetallic compound (IMC) formation between the deposits and Cu substrate and surface oxidation after ambient storage were examined. During electrodeposition, the plumbous (Pb <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) ions were observed to inhibit stannous (Sn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2+</sup> ) ion reduction. The use of a metallographic cross sectioning approach enabled the observation of a grain structure evolution toward a more equiaxed morphology with increasing Pb content. This was accompanied by a duplex-phase structure consisting of isolated Pb-rich particles at grain boundary intersections together with a continuous Sn-rich phase. X-ray diffraction measurements corroborate the existence of the duplex-phase structure and also indicate an as-deposited texture transition from (112) through (200) and further toward (220) with an increase in Pb content from 0 to 8 wt.%. A marked topological transition of the interfacial Cu-Sn IMCs from wedge-shaped and discretely distributed to relatively even and uniformly distributed was found to occur concurrently. After tin whisker growth had occurred from low-Pb content (up to 5 wt.%) electrodeposits on brass, Pb was generally observed to be strongly associated with actual Sn whiskers themselves, thus the spontaneous redistribution of Pb after electrodeposition has been evidenced. X-ray photoelectron spectroscopy sputter profiling indicates the absence of Pb in the Sn oxide layer and the enrichment of metallic Pb beneath the Sn oxide from a 90Sn-10Pb deposit ambient stored for 270 days. The whisker-inhibiting effect of Pb codeposition is postulated to emanate from more than one source: not only those reflected in grain structure modification, grain texture transition, and changes in the growth mode of the interfacial Cu-Sn IMCs as prevailingly acknowledged, but also significantly, the universal distribution of the soft Pb-rich phase, providing simultaneous diffusion toward potential whisker sites as well as effective strain dissipation.

Enhanced Magnetization of Sol‐Gel Synthesized Pb‐Doped Strontium Hexaferrites Nanocrystallites at Low Temperature

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12−xO19 (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized by sol‐gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M‐type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution. The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required. The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature.

Influence of Pb doping on the electrical transport properties of BiCuSeO

The effect of Pb doping on the thermoelectric properties of p-type BiCuSeO from 25 K to 873 K has been studied. The electrical resistivity and Seebeck coefficient of Bi1−xPbxCuSeO both decreased monotonically in all temperature range with increasing Pb content due to the increased carrier concentration. The power factor of Bi1−xPbxCuSeO (x = 0.03) reaches 5.3 μW cm−1 K−2 at 873 K. The influence of Pb2+ doping on the electronic structure is the same as the one obtained with Sr2+, however, the decrease of the holes mobility is reduced as compared to Sr2+ doping, which could be beneficial to the thermoelectric performances.

On-line phase transitions of bulk and nanocrystalline La1−xPbxMnO3 (x = 0.3, 0.4, and 0.5) perovskite manganite materials using ultrasonic measurements

Bulk and nanostructured La1−xPbxMnO3 perovskite manganite samples for different Pb contents (x=0.30, 0.40 and 0.50) were synthesised using solid-state reaction and sonochemical methods, respectively. XRD, FTIR, SEM, EDAX, BET and TEM studies were carried out to characterise the prepared bulk and nanosamples. The XRD characterization studies confirmed that the prepared bulk and nano perovskite manganite samples were crystalline in nature. The SEM and TEM studies revealed that the particle sizes of bulk perovskite samples is in the range of 0.75–85μm, whereas it ranges from 50 to 90nm in the case of nano perovskite samples. Further, it has been confirmed that there is an increase in particle size with an increase in Pb content both in bulk and nano perovskite samples. In addition, ultrasonic velocities and attenuations of bulk and nanosamples were measured using the on-line ultrasonic through transmission method. The temperature-dependent ultrasonic parameters showed an interesting anomaly in both bulk and nano perovskite samples. The observed marked softening and hardening in sound velocities and attenuation were related to ferromagnetic to paramagnetic phase transition temperature (TC). In nano perovskites samples, the existence of diffused phase transition took place at a lower temperature compared with the corresponding bulk samples. The observed broad ferromagnetic (FM)–paramagnetic (PM) transition in nano perovskites confirms the absence of sharp transition, which is attributed to the coexistence of orbitally, ordered and disordered phases. The spin–phonon and electron–phonon couplings are known to exist because of single ion magnetostriction and dynamic Jahn–Teller effect, respectively, are evidenced by the observed anomalies in both velocities and attenuations.

Influence of Pb doping on structural, electrical and magnetic properties of Sr-hexaferrites

Sol–gel auto-ignition technique was used for the synthesis of Pb-doped strontium ferrites with compositions Sr1−xPbxFe12O19 (x=0.00, 0.05, 0.10, 0.15, 0.20). Sintering of the samples at 800°C for 2h developed a stable hexagonal phase which was confirmed by X-ray diffraction analysis. Lattice parameters and unit cell volume were calculated utilizing the data received from this analysis and it was observed that their values were increased with increasing concentration of Pb doping. The Pb doping decreased the porosity making the ferrites samples more compact. A small increase in crystallite size, determined with the help of Scherrer’s formula, could be attributed to the substitution of Pb2+ having slightly larger ionic radius than that of Sr2+. Frequency and temperature dependent dielectric constant and dielectric tangent loss were determined for all the compositions, and it was observed that their values were decreased with the increase in frequency and increased slightly with the increase in temperature of the samples. The increase in Pb contents decreased dielectric constant and dielectric tangent loss that favors the use of materials in high frequency appliances. The magnetic properties of the samples were investigated, using a vibrating sample magnetometer and the results showed that the increasing ratio of diamagnetic Pb decreased saturation magnetization and remanence, and increased the coercivity that made the materials useful for the fabrication of devices which require hard magnetic properties.

Electrical properties of non-stoichiometric PZT 95/5 ferroelectric ceramics

Pb0.99(Zr0.95Ti0.05)0.98Nb0.02O3 (denoted as PZT 95/5) ceramics were prepared according to the nominal composition of Pb0.99+x (Zr0.95Ti0.05)0.98Nb0.02O3+x (−0.01 ≤ x ≤ 0.04). The electrical properties as a function of lead oxide (Pb) stoichiometry were evaluated. X-ray diffraction analysis shows that all the as-synthesized PZT 95/5 powders are pure perovskite phase and the unit cell volume increases with the addition of Pb. SEM micrographs indicate the fracture mode tends to be predominately intergranular and grain size gets bigger with the increase of Pb content. The coercive field decreases with the increase of Pb till x = 0.02 and then increases when the excess Pb is over x = 0.02. The remnant polarization first increases and then decreases with the increasing amount of excess Pb. Sample with excess Pb x = 0.03 has the biggest value of remnant polarization.

Variations in Structural and Electrical Properties of Ba-Hexaferrite due to Pb Substitution

BaFe2-xPbxO9 (x=0.0 to 1.0) samples were prepared by co-precipitation method. All samples were sintered at 960±5°C for three hours. Structural properties were investigated by X-ray diffraction (XRD) and Scanning electron microscopy (SEM). Variation in structural parameters was calculated from XRD obtained data. SEM micrographs were used to study the morphology and grain growth. No regular increase or decrease in structural parameters and morphology is observed with increase in Pb content. For dc electrical characterizations, dc resistivity was measured as a function of temperature up to 750K. Data obtained was further analyzed and different dc parameters like activation energy and mobility were measured. For dielectric analysis, capacitance C was measured in the frequency range from 100 kHz to 3MHz. High dielectric constant for this material makes this material suitable for applications like multilayer capacitors (MLC), microwave devices and dynamic random access memory (DRAM).

Composition-dependent metal-insulator transition in perovskite CaXPb(1−X) TiO3 (CPT) ceramic

Ceramic compositions of a complex perovskite CaXPb(1−X)TiO3 (CPT) systems with x=0.6, 0.7 and 0.8 were prepared by mechanical mixing of their oxides (CaTiO3 and PbTiO3). The structure of the (CPT) ceramics was characterized by X-ray diffraction (XRD) The ceramics transform gradually from orthorhombic phase (pseudo cubic phase) to cubic phase by increasing pb content percent. The dc resistivity ρ(t) versus temperature (range 300–525K) for x=0.6, 0.7 and 0.8. The ρ.T/curves reveal that samples exhibit a metallic behaviour at low temperature and undergo a metal-semiconductor transition with increasing temperature at Tp=373K, 343K and 333K, for x=0.6, 0.7 and 0.8, respectively. The nature of conduction mechanism is studied in semiconductor region by studying the current–voltage temperature characteristics. The current–voltage characteristics were interpreted in terms of Poole–Frenkel type of conduction mechanism.

Physical properties of La1−xPbxMnO3 perovskites with 0.24 ≤ x ≤ 0.40

The La1−xPbxMnO3 perovskites with 0.24≤x≤0.40 crystallize in a rhombohedral structure having R3¯c space group. The temperature dependences of the lattice parameters for samples with x=0.24 and 0.40 evidenced no structural phase transitions between 10 and 295K. The saturation magnetizations, at 4.2K, increase as the Pb content is higher. A gradual transition from spin glass to ferromagnetic ordering was shown as the Pb content increases. Paramagnetic measurements and X-ray photoelectron spectroscopy studies evidenced that the relative content of Mn4+ ions is close to that of Pb2+ ions. The resistivities increase with temperature and a metallic to semiconducting transition is shown at temperatures smaller than the Curie points. The field and temperature dependences of the magnetoresistivities were analysed.

Pb-DOPING EFFECTS ON THE DIELECTRIC AND PYROELECTRIC PROPERTIES OF (Sr,Pb)TiO3 SYSTEM

Lead strontium titanate ( Sr 1-x Pb x) TiO 3 (0.20 ≤ x ≤ 0.45,step = 0.05) ceramics were prepared by conventional mixed oxide method. The X-ray diffraction patterns indicate that the prepared samples have perovskite-type structure. With the increase of Pb content, there is a tendency from the cubic to tetragonal structure. The scanning electron microscopy micrographs reveal that the addition of Pb can affect microstructure. The dependent temperature dielectric permittivity and dielectric loss were investigated in the frequency range from 100 Hz to 1 MHz. The maximum peak of the dielectric permittivity versus temperature curve was broadened and a frequency dispersion of the dielectric permittivity was observed for the (Sr0.8Pb0.2)TiO3 ceramics. The results obtained at the frequency of 10 kHz reveal the Curie temperature linearly increased with the lead content. The fitted curves of temperature versus inverse dielectric permittivity at 10 kHz for ( Sr 1-x Pb x) TiO3 ceramics are consistent with Curie–Weiss law. The Pyroelectric properties were also investigated. The high pyroelectric coefficients and figure of merits indicate that the SPT ceramics are potential materials for pyroelectric sensors.

Biomass and Yield of Peanut Grown on Tropical Soil Amended with Sewage Sludge Contaminated with Lead

Application of sewage sludge with high lead (Pb) contents may pollute soils and contaminate crops. The objective of this work was to evaluate peanut responses to application of sewage sludge with varying Pb contents in order to supply phosphorus (P) to the plant. A greenhouse experiment was carried out with peanut grown on soil sample from a medium-textured Haplustox. Treatments were arranged in 3 × 2 + 2 factorial scheme, replicated three times, distributed in randomized block design, and consisted of: three Pb rates applied to soil with sewage sludge (3, 21, and 42 mg kg−1) × two times of sewage sludge application (30 days before peanut sowing and at the day of the sowing) + mineral fertilization + control (without sewage sludge and mineral fertilization). Sewage sludge was efficient to supply P to peanut. Sewage sludge containing high rates of Pb, when applied, did not harm biomass and yield of the plant, but increased HCl-extractable Pb in soil and Pb content in shoot, roots, and pod husks. Increase of Pb content in pod husks may represent contamination risk of kernels and their products with fragments from husks detached during manipulation or industrial processing of peanuts.

Distribuição e assinatura isotópica de Pb em sedimentos de fundo da Foz do Rio Guamá e da Baía do Guajará (Belém - Pará)

Lead analyses in bottom sediments from the hydrographic system of Belem (Para) indicated low contents of this metal for the sediments from the Guama river, with no significant anthropogenic contribution. A concentration of 18.1 ± 1.5 mg kg-1 and 206Pb/207Pb isotopic signature of 1.196 ± 0.002 are assigned for Pb from natural sources. On the other hand, the significant increase of Pb contents in the sediments from the Guajara bay, together with the decrease of 206Pb/207Pb ratios (1.172 < 206Pb/207Pb < 1.188) point to an anthropogenic lead contribution, originated by the industrial and urban activities of the city of Belem.

Thermoelectric Performance of AgPb x SbTe20 (x = 17 to 23) Bulk Materials Derived from Large-Particle Raw Materials

AgPbxSbTe20 (x = 17 to 23) bulk materials with nanometer-sized grains were fabricated by combining mechanical alloying (MA) and spark plasma sintering (SPS) intentionally using large-sized lead and tellurium particles as raw materials to reduce oxygen impurity from surface oxides. It was found that the nominal Pb content in the starting powder mixture greatly affected the thermoelectric (TE) properties of the sintered bulk samples, with excess amount relative to the stoichiometric ratio of AgPbmSbTem+2 less than previously reported. x-Ray diffraction experiments revealed that the lattice parameter increases linearly with increasing Pb content until x = 20, which corresponds to the optimal nominal Pb content in the starting composition, showing the highest ZT value. A high ZT value of 1.2 at 675 K was achieved in the x = 20 sample due to its lowest electrical resistivity and reduced thermal conductivity. The present study shows that using large-sized Pb particles containing less oxygen is suitable for fabrication of AgPbmSbTem+2-system TE materials by MA and SPS processes.

Constitutive Behavior of Mixed Sn-Pb/Sn-3.0Ag-0.5Cu Solder Alloys

During the transition from Pb-containing solders to Pb-free solders, joints composed of a mixture of Sn-Pb and Sn-Ag-Cu often result from either mixed assemblies or rework. Comprehensive characterization of the mechanical behavior of these mixed solder alloys resulting in a deformationally complete constitutive description is necessary to predict failure of mixed alloy solder joints. Three alloys with 1 wt.%, 5 wt.%, and 20 wt.% Pb were selected so as to represent reasonable ranges of Pb contamination expected from different 63Sn-37Pb components mixed with Sn-3.0Ag-0.5Cu. Creep and displacement-controlled tests were performed on specially designed assemblies at temperatures of 25°C, 75°C, and 125°C using a double lap shear test setup that ensures a nearly homogeneous state of plastic strain at the joint interface. The observed changes in creep and tensile behavior with Pb additions were related to phase equilibria and microstructure differences observed through differential scanning calorimetric and scanning electron microscopic cross-sectional analysis. As Pb content increased, the steady-state creep strain rates increased, and primary creep decreased. Even 1 wt.% Pb addition was sufficient to induce substantially large creep strains relative to the Sn-3.0Ag-0.5Cu alloy. We describe rate-dependent constitutive models for Pb-contaminated Sn-Ag-Cu solder alloys, ranging from the traditional time-hardening creep model to the viscoplastic Anand model. We illustrate the utility of these constitutive models by examining the inelastic response of a chip-scale package (CSP) under thermomechanical loading through finite-element analysis. The models predict that, as Pb content increases, total inelastic dissipation decreases.

Effects of duration of exposure to dietary lead on rumen metabolism and the accumulation of heavy metals in sheep

The duration of exposure of sheep to dietary Pb may affect their ability to manage the toxic effects of the Pb, as well as influencing the metabolism of other heavy metals. Sheep were exposed to a supplement of 34mg Pb/kg basal diet DM for 3, 6 or 9 weeks. Compared with 3-week exposure, rumen contents after 6 weeks had increased Pb content (P=0.02), and after 9 weeks had reduced Cu (P=0.01) and Cr (P=0.04) concentrations. The longer exposure periods reduced digestion of long particles, and increased the alkali buffering potential in the rumen, but duration of exposure to Pb did not affect its proportional absorption (P=0.26). Most additional Pb was excreted in faeces or accumulated in the bones and spleen, and urinary Pb output was increased (P<0.01) after exposure for 6 or 9 weeks. Proportional absorption of Cd was increased after 6 and 9 weeks of Pb exposure, compared to 3 weeks (P<0.01), and after 6 weeks renal Cd had increased from 4 to 9mg/kg (P<0.01), which is above the normally accepted legal maximum concentration of 4.8mg/kg. After 9 weeks of Pb exposure Cd had declined in the kidney and increased in blood cells. It is concluded that duration of exposure to Pb did not affect its absorption, and there was no evidence of protective mechanisms, but extended exposure caused increased accumulation of Cd that rendered renal concentrations above legal limits.

LEAD CONTAMINATION LEVELS IN ROADSIDE VEGETATION OF GHARIAN-TRIPOLI ROAD, LIBYA

This study was designed to determine the lead contamination in roadsides vegetation along 125 km of busy roads resulting from many sources such as the exhaust of cars that use gasoline. The area of this study was Gharian city center, and the sides of Gharian-Azizia, Azizia-Swani, Swani-Airport and Airport-Tripoli Roads. Samples were collected from the leaves of plants adjacent to public roads within the study area by distance of 2-5 km between samples within urban centers and 10-15 km within the roads, so as to give a true representation of the study area. Results of this study showed that the traffic volume caused a significant increase in Pb content in roadside vegetation. Higher Pb concentrations were found in sites with a higher traffic volume on main roads. Results showed that the rate of lead contamination varied within the study area, but generally less than 50.99 µg/100cm2. It was found that the highest percentage of pollution within the city center of Azizia with 50.99 µg/100cm2, followed by Gawasem center with 43.65 µg/100cm2 while the lowest polluted area was Azizia-Swani road with 11.58 µg/100cm2. The presence of elevated levels of lead on/in the plants closer to the roads with high traffic density caused by the use of alkyl lead compounds as antiknock and freezing additives in fuel needs more attention and some necessary steps should be adopted.

Structure and composition-dependent optical properties of (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotube arrays

AbstractLead strontium titanate (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes were synthesized by sol-gel template method via spin coating. The structures and morphology of the as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy and transmission electron microscopy. X-ray photoelectron spectroscopy was used to determine the chemical composition of the sample and the valence state of elements. Raman spectroscopy of the as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes at room temperature was also investigated. The results indicate that as-prepared (PbxSr1–x)TiO3 (x=0.4, 0.6) nanotubes are perfectly crystallized and there is a trend of structure change from PST40 to PST60. A weak peak at 508 cm−1 assigned to E(3TO) mode can be seen in the Raman spectrum of (Pb0.6Sr0.4)TiO3 sample. Photoluminescence spectra of samples at room temperature reveal three intense emission bands centered at 356, 400 nm for (Pb0.4Sr0.6)TiO3 and 413, 433, 451 nm for (Pb0.6Sr0.4)TiO3 nanotubes, respectively. The peak positions of the emission band have a significant blue shift as Pb content increases.

Effect of Pb doping on structural and electrochemical properties of combustion synthesised LiCoO2 powder

Pb-doped LiCoO2 cathode materials, containing 0–10 mol% of Pb were synthesised by the starch-assisted combustion technique. X-ray diffraction analyses revealed the existence of rhombohedral LiCoO2 (R-3m) for all compounds. Scanning electron microscopy showed a distinct grain growth with increasing Pb content. The synthesised samples are characterised using X-ray photoelectron spectra (XPS), to investigate the elementary states on the system. The electrical conductivity of Pb-doped LiCoO2 system tends to increase with Pb content significantly. Decrease of the electrode impedance was observed with increase in Pb content in system. An excellent reversible capacity was observed for the cathode containing 5.0 mol% Pb, when 2016 type coin cells were cycled at 0.1 C rate. This has been ascribed to the structural stability induced by Pb doping.