Effect of AC&DC field on the dielectric response of (Pb,La)TiO3 thin films

Lanthanum doped lead titanate thin films are the potential candidates for the capacitors, actuators and pyroelectric sensor applications due to their excellent dielectric, and ferroelectric properties. Lanthanum doped lead titanate thin films are grown on platinum coated Si substrates by excimer laser ablation technique. A broad diffused phase transition with the maximum dielectric permittivity (ϵmax) shifting to higher temperatures with the increase of frequency, along with frequency dispersion below Tc, which are the signatures of the relaxor like characteristics were observed. The dielectric properties are investigated from −60°C to 200°C with an application of different dc fields. With increasing dc field, the dielectric constant is observed to reduce and phase transition temperature shifted to higher temperature. With the increased ac signal amplitude of the applied frequency, the magnitude of the dielectric constant is increasing and the frequency dispersion is observed in ferroelectric phase, whereas in paraelectric phase, there is no dispersion has been observed. The results are correlated with the existing theories.

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.

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.

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.

On the densification mechanisms and properties of Cu-Pb and Cu-Pb-TiB2 nanocomposites densified using spark plasma sintering

The present paper is aimed to understand the sub-processes triggered by rapid heating during spark plasma sintering as well as to assess the extent to which densification and properties of metallic materials can be enhanced using such superfast consolidation process. Using nanocrystalline Cu-Pb as a model system, the influence of Pb as well as TiB2 addition on the densification mechanisms and properties are discussed. Importantly, a high hardness of 2 GPa is achieved in Cu-based nanocomposites. (C) 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Melting and solidification behavior of Pb-Sn embedded alloy nano-particles

Nano-sized bimetallic dispersoids consisting of (Pb) and beta-(Sn) phases of eutectic composition (Pb26.1Sn73.9) embedded in aluminum and Al-Cu-Fe quasicrystalline matrices have been prepared by rapid solidification processing. The two phases, face centered cubic (Pb) and body center tetragonal, beta-(Sn) solid solution co-exist in all the embedded nanoparticles at room temperature. The phases bear crystallographic orientation relationship with the matrix. In situ TEM study has been carried out for the alloy particles to study the melting and the solidification behavior. The detailed microscopic observations indicate formation of a single-phase metastable fcc (Pb) in the nano-particles prior to the melting during heating. Solidification of these particles begins with nucleation of fcc (Pb), which phase separates into fcc (Pb) and beta-(Sn) lamellae in the solid state. In situ X-ray diffraction study is carried out to obtain lattice parameter of metastable fcc (Pb) and thereby an estimate of amount of Sn dissolved in the metastable (Pb) prior to the melting. The results are discussed in terms of a metastable phase diagram between fcc Pb and fcc Sn and invoking the size effect on the metastable phase diagram. The size factor is found to play a critical role in deciding the pathway of phase transformation as well as the extension of solid solubility of Sn in fcc (Pb) in the nano-particles.

Fretting wear study of Cu-10 wt% TiB2 and Cu-10 wt% TiB2-10 wt% Pb composites

In developing materials with better tribological properties, it is always conceived that the addition of softer phase would result in better frictional behavior. In order to address this issue, we report here the results of fretting wear study on Cu-10 wt% TiB2 and Cu-10 wt% TiB2-10 wt% Pb composites, sintered using spark plasma sintering (SPS) technique. It was found out that the addition of softer phase i.e. 10 wt % Pb to Cu-10 wt% TiB2 composites has not resulted in the lowering of the coefficient of friction (COF). The combination of steady state COF (0.6) and wear rate (10(-3) mm(3)/N-m) was measured and such properties are even better than that obtained with TiB2 coatings reported in the literature. For Cu-10 wt% TiB2 sintered at different temperature, a lower wear resistance with increase in hardness is being measured. An attempt has been made to correlate the observed wear behavior with the surface and subsurface deformation. The formation of a wear-resistant delaminated tribolayer consisting of TiB2 particles and ultrafine oxide debris (Cu, Fe, Ti)(x)O-y was the reason assigned for the observed low wear rate of these composites. (C) 2013 Elsevier B.V. All rights reserved.

Microstructure-Wear Resistance Correlation and Wear Mechanisms of Spark Plasma Sintered Cu-Pb Nanocomposites

The dispersion of a softer phase in a metallic matrix reduces the coefficient of friction (COF), often at the expense of an increased wear rate at the tribological contact. To address this issue, unlubricated fretting wear tests were performed on spark plasma sintered Cu-Pb nanocomposites against bearing steel. The sintering temperature and the Pb content as well as the fretting parameters were judiciously selected and varied to investigate the role of microstructure (grain size, second-phase content) on the wear resistance properties of Cu-Pb nanocomposites. A combination of the lowest wear rate (similar to 1.5 x 10(-6) mm(3)/Nm) and a modest COF (similar to 0.4) was achieved for Cu-15 wt pct Pb nanocomposites. The lower wear rate of Cu-Pb nanocomposites with respect to unreinforced Cu is attributed to high hardness (similar to 2 to 3.5 GPa) of the matrix, Cu2O/Fe2O3-rich oxide layer formation at tribological interface, and exuding of softer Pb particles. The wear properties are discussed in reference to the characteristics of transfer layer on worn surface as well as subsurface damage probed using focused ion beam microscopy. Interestingly, the flash temperature has been found to have insignificant effect on the observed oxidative wear, and alternative mechanisms are proposed. Importantly, the wear resistance properties of the nanocomposites reveal a weak Hall-Petch-like relationship with grain size of nanocrystalline Cu. (C) The Minerals, Metals & Materials Society and ASM International 2013

Co-existence of tetragonal and monoclinic phases and multiferroic properties for x <= 0.30 in the (1-x)Pb(Zr0.52Ti0.48)O-3-(x)BiFeO3 system

Compositions with x <= 0.30 in the system (1- x)Pb(Zro(0.52)Ti(0.48))O-3-(x)BiFeO3 were synthesized by sol-gel method. Rietveld analysis of X-ray diffraction data reveals tetragonal structure (P4mm) for x <= 0.05 and monoclinic (Cm) phase along with the existence of tetragonal phase for 0.10 <= x <= 0.25 and monoclinic phase for x = 0.30. Transformation of E(2TO) and E + B1 vibrational modes in the range 210-250 cm(-1) (present for x <= 0.25) into A' + A `' modes at similar to 236 cm(-1) for x = 0.30, and occurrence of new vibrational modes A' and A `' in Raman spectra for x >= 0.10 unambiguously support the presence of monoclinic phase. Occurrence of remnant polarisation and enhanced magnetization with concentration of BiFeO3 indicates superior multiferroic properties. Variation of magneto-capacitance with applied magnetic field is a strong evidence of magneto-electric multiferroic coupling in these materials. (C) 2014 Elsevier B.V. All rights reserved.

Iminodiacetic acid functionalized polypyrrole modified electrode as Pb(II) sensor: Synthesis and DPASV studies

An electrochemical lead ion sensor has been developed by modification of carbon paste electrode (CPE) using polypyrrole functionalized with iminodiacetic acid (IDA-PPy) containing carboxyl group. The electrochemical response of Pb2+ ion on the IDA-PPy modified CPE has been evaluated and the controling parameters have been optimized using differential pulse anodic stripping voltammetry (DPASV). The IDA-PPy modified CPE shows a linear correlation for Pb2+ concentrations in the range of 1 x 10(-6) to 5 x 10(-9) M and the lower detection limit of Pb2+ has been found to be 9.6 x 10(-9) M concentration. Other tested metal ions, namely Cu2+, Cd2+, Co2+, Hg2+, Ni2+ and Zn2+, do not exhibit any voltammetric stripping response below 1 x 10(-7) M concentration. However, the Pb2+ response is affected in the presence of molar equivalents or higher concentrations of Cu2+, Cd2+ and Co2+ ions in binary systems with Pb2+, consequent to their ability to bind with iminodiacetic acid, while Hg2+, Ni2+ and Zn2+ do not interfere at all. A good correlation has been observed between the lead concentrations as analyzed by DPASV using IDA-PPy modified CPE and atomic absorption spectrophotometry for a lead containing industrial effluent sample. (C) 2014 Elsevier Ltd. All rights reserved.

Microstructure-hardness-fretting wear resistance correlation in ultrafine grained Cu-TiB2-Pb composites

The retention of the desired combination of mechanical/tribological properties in ultrafine grained materials presents important challenges in the field of bulk metallic composites. In order to address this aspect, the present work demonstrates how one can achieve a good combination of hardness and wear resistance in Cu-Pb-TiB2 composites, consolidated by spark plasma sintering at low temperatures ( < 500 degrees C). Transmission electron microscope (TEM) studies reveal ultrafine grains of Cu (100-400 nm) with coarser TiB2 particles (1-2 mu m) along with fine scale Pb dispersoid at triple junctions or at the grain boundaries of Cu. Importantly, a high hardness of around 2.2 GPa and relative density of close to 90% relative density (rho(theo)) have been achieved for Cu-15 wt% TiB2-10 wt% Pb composite. Such property theo, combination has never been reported for any Cu-based nanocomposite, by conventional processing route. In reference to the tribological performance, fretting wear tests were conducted on the sintered nanocomposites and a good combination of steady state COF (0.6-0.7) and wear rate (10-4 mm(3)/N m) were measured. An inverse relationship between wear rate and hardness was recorded and this commensurates well with Archard's relationship of abrasive wear. The formation of a wear-resistant delaminated tribolayer consisting of TiB2 particles and ultrafine oxide debris, (Cu, Fe, Ti)(x)O-y as confirmed from subsurface imaging using focused ion beam microscopy has been identified as the key factors for the low wear rate of these composites. (C) 2014 Elsevier B.V. All rights reserved.

On the Room Temperature Ferromagnetic and Ferroelectric Properties of Pb(Fe1/2Nb1/2)O-3

We report the origin of room temperature (RT) ferromagnetic and ferroelectric properties of Pb(Fe1/2Nb1/2)O-3 (PFN) ceramic sample prepared by modified solid-state reaction synthesis by a single-step method, based on X-ray diffraction (XRD), neutron diffraction (ND), Mossbauer spectroscopy and electron paramagnetic resonance (EPR) spectroscopy results. Formation of single-phase monoclinic PFN ceramic with Cm space group was confirmed by XRD and ND at RT. The morphology studied by scanning electron microscopy (SEM) confirmed uniform microstructure of the sample with average grain size of similar to 2 mu m. The ND, Mossbauer spectroscopy, M-H loop and EPR studies were carried out to confirm the existence of weak ferromagnetism at RT. A clear opening of hysteresis (M-H) loop is evidenced as the existence of weak ferromagnetism at RT. EPR spectrum clearly shows the ferromagnetism through a good resonance signal. The symmetric EPR line shape with g = 1.9895 observed in PFN sample was identified to be due to Fe3+ ions. Mossbauer spectroscopy at RT shows superparamagnetic behaviour with presence of Fe in 3+ valence state. Ferroelectric P-E loops on PFN at RT confirm the existing ferroelectric ordering. Our observation is in agreement with literature, and it supports that the origin of ferromagnetism and ferroelectricity is isolated, i.e. from different regions in the sample. Our results do not support the multiferroic nature of PFN at RT.