Pb Phase Research Articles

Magnetoelectric Coupling in Disordered Multiferroics

Higher order magnetoelectric effects dominate in disordered multiferroics with broken translational symmetry such as multiglassy Sr0.98Mn0.02TiO3, antiferromagnetic quantum paraelectric EuTiO3, relaxor ferroelectric antiferromagnetic Pb(Fe0.5Nb0.5)O3, and antiferroelectric antiferromagnetic CuCr1-xInxP2S6. The E 2 H 2 effect is allowed in all symmetries. In EuTiO3 it is due to biquadratic coupling between spins and soft phonon pseudospins and yields ‘giant’ values at critical magnetic fields. Weak magnetoelectric coupling is due to spin or dipole glass phases in Pb(Fe0.5Nb0.5)O3 and CuCr1-xInxP2S6, respectively. EH effects are observed after field-induced ordering, e.g. in EuTiO3 or in the spin glass phase of Pb(Fe0.5Nb0.5)O3.

Antiferroelectric–ferroelectric phase boundary enhances polarization extension in rhombohedral Pb(Zr,Ti)O3

The main mechanism of properties enhancement in the morphotropic phase boundary region separating tetragonal and rhombohedral phases of Pb(Zr1-xTix)O3 (PZT) is related to polarization rotation. It is shown here that in proximity of the morphotropic phase boundary separating antiferroelectric and rhombohedral phases (near x = 0.1) and at elevated temperatures the properties are dominated by polarization extension. These results may provide a guideline for developing alternative piezoelectric materials to PZT.

Occurrence, speciation and bioaccessibility of lead in Chinese rural household dust and the associated health risk to children

Abstract Lead (Pb) concentration, speciation and bioaccessibility were measured in 122 household dust samples collected in rural areas of eight provinces of China. The mean Pb concentration in the household dust was 208 mg kg−1, of which samples from sites in Hunan (538 mg kg−1) and Yunnan (280 mg kg−1) provinces exhibited the highest Pb concentrations while those from Shaanxi (96 mg kg−1) and Fujian (80 mg kg−1) provinces had a relatively low Pb content. The major fraction of Pb in the household dust samples was found to be strongly bound to Fe–Mn oxide phases (37%) while Pb present in minor fractions individually making up between 14 and 18% was characterized in falling orders as residual, carbonate, organic/sulphide, and exchangeable fractions by the sequential extraction method applied. Bioaccessible Pb making up an average proportion of 53% in the household dusts was significantly correlated to the Fe–Mn oxide phases of Pb. According to the Hazard Quotient (HQ), the ingestion of dust particles pose the highest risk to children in Chinese rural areas, followed by dermal contact and inhalation. Hazard Index (HI) values for most samples were lower than 1, indicating that the domestic Pb exposure in rural areas of China were relatively safe for children when they exposure to the household dust. However, dust Pb in 4.1% of the studied families having HI values higher than 1 may pose adverse health effect to the children.

Effect of pressure on electric generation of PZT(30/70) and PZT(52/48) ceramics near phase transition pressure

Abstract Impact experiment of Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.52Ti0.48)O3 ceramics were conducted by empolying shock reverberation techniques within 3–7 GPa and X-ray diffraction patterns of these materials have been measured at pressure up to 32 GPa with a diamond anvil cell and synchrotron radiation. To refine the crystal structure, Rietveld analysis was performed and bulk moduli were calculated using Birch-Murnaghan equation of state. We found a tetragonal phase transforming to a cubic phase in Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.52Ti0.48)O3 ceramics at ∼7.4 GPa and ∼4 GPa respectively. For dynamic pressure experiment, a metal flyer accelerated by a gas gun facility impacts into PZT ceramics to investigate electric energy. As pressure increased, output voltage of Pb(Zr0.3Ti0.7)O3 and Pb(Zr0.52Ti0.48)O3 ceramics slightly increased below ∼7 GPa and ∼4 GPa. But the voltage increased near ∼7 GPa and ∼4 GPa. From the result, we could confirm that the phase transition influenced the considerable effect on the electrical power generation.

Thermal stability and elastic properties of Mg2X (X = Si, Ge, Sn, Pb) phases from first-principle calculations

Thermal stabilities, elastic properties and electronic structures of Mg2Si, Mg2Ge, Mg2Sn and Mg2Pb have been determined from first-principle calculations. The calculated heats of formation and cohesive energies show that Mg2Ge has the strongest alloying ability and Mg2Si has the highest structural stability. Gibbs free energy, heat capacity and Debye temperature are calculated and discussed. The elastic parameters are calculated, the bulk moduli, shear moduli, Young’s moduli and poisson ratio value are derived, the brittleness and plasticity of these phases are discussed, and the brittle behavior and structural stability mechanism are also explained through the densities of states (DOS) of these intermetallic compounds.

Role of TiO2 Seed Layer Thickness on the Nanostructure Evolution and Phase Transformation Behavior of Sputtered PZT Thin Films During Post‐Deposition Air‐Annealing

An optimum TiO2 seed layer is said to facilitate nucleation and subsequent growth of perovskite phase in Pb(Zr,Ti)O3 (PZT) films during annealing. The actual causes that prevent perovskite growth, particularly in sputtered PZT films on thick TiO2 seed layers are not yet understood clearly. Herein, based on the results of X‐ray diffractometry (XRD), field‐emission scanning electron microscopy (FESEM), and analytical scanning/transmission electron microscopy (S/TEM) with semi‐quantitative elemental mapping using energy dispersive X‐ray (EDX) spectrum imaging, the post‐annealing crystallization trend of r.f. magnetron sputter‐deposited amorphous PZT films has been scrutinized as a function of TiO2 seed layer thickness. Upon annealing, PZT films on thin TiO2 layers (~20–100 nm) partially crystallize into perovskite PZT via a transient pyrochlore/fluorite phase. However, no perovskite phase forms on thicker (~550 nm) TiO2 layer. Thickness of underlying TiO2 seed layer strongly influences the crystallization, phase formation, texture, and surface morphology of the PZT films. During crystallization, Pb diffuses away from the PZT film to form solid solution with TiO2 seed layer. Perovskite PZT phase transformation requires a minimum Pb‐concentration within the transient pyrochlore/fluorite phase. During the growth of perovskite grains, Zr gets segregated, resulting in Zr‐concentration build‐up within the surrounding disordered fcc fluorite phase.

Mineralogy and chemical forms of lead and zinc in abandoned mine wastes and soils: An example from Morocco

Chemical extractions coupled with quantitative X-ray powder diffraction (XRPD) were used to define the chemical and mineralogical forms of Pb and Zn in abandoned wastes and soils from the Upper Moulouya mining district (Morocco). The aim was to provide baseline data required to assess metal mobility and bioavailability. Wastes and soils were sampled inside the mine sites of Zeïda, Mibladen and Aouli, both in exploitation and processing areas. Additional potentially unaffected soil samples were taken outside the Mibladen site. pH of wastes and soils is alkaline as a consequence of carbonate abundance (on average 36%). Total Pb and Zn concentrations have a wide spread of values (Pb: 0.041–17.25gkg−1; Zn: 0.051–276.5gkg−1), with tailings from all mines and soils from Mibladen processing area exhibiting the highest concentrations. Very low or no detectable contamination characterizes the soils from exploitation areas and those collected outside Mibladen. Zinc contamination is mainly restricted to Mibladen processing area, where Zn ores from other Moroccan mines were possibly processed. The sequential extraction procedure for metal fractionation indicates that in contaminated samples Pb and Zn are mainly present in the acetic acid extractable fraction, likely as carbonates, (Pb up to 80%; Zn up to 52%), while in less or not contaminated soils both metals are mostly associated with the reducible fraction, presumably as iron oxides (Pb up to 68%; Zn up to 80%). Eight minerals containing Pb and Zn were identified: cerussite, anglesite, galena, hydrozincite, smithsonite, sphalerite, willemite and hemimorphite. Cerussite is the most important Pb-host. Hemimorphite and smithsonite account for most Zn. According to the alkaline conditions and to the low solubility of Pb and Zn mineral phases, it can be suggested that within the studied environment mobilization into solution in aqueous systems and bioavailability of Pb and Zn have a low potential. Nevertheless, given aridity and strong winds, inhalation of airborne particulates may be a concern.

Formation and Growth of Intermetallic Compound Layers at Interface of Solder/Copper Alloys for Lead Frame

The effect of chemical species of copper alloys on growth of intermetallic compounds (IMCs) at interface of solder/copper alloys for lead frame was investigated. The results have revealed that Cu is the main diffusing species during aging. After aged at 160°C for 300h, only a Cu6Sn5IMC layer is observed at SnPb/copper alloys interfaces. The growth rate of IMC on the Cu-Cr-Zr system alloys and Cu-Ni-Si alloys was much slower than that of IMC on the C19400 alloy. The Pb phase and voids were found to be inside the Cu6Sn5phase. Chromium, one of the alloying element in Cu-Cr-Zr-Zn alloys, has found to be segregated at the interface between the copper alloy/Cu6Sn5. Zn and Zr in the Cu-Cr-Zr-Zn system alloy are enriched in small amout inside the IMC. These observed results were discussed and analysed on the baisis of diffusion and growth kinetics.

Synthesis and optical properties of elliptic Pb(OH)Br microdiskettes

The novel elliptic Pb(OH)Br microdiskettes were controllably synthesized by a simple sonochemical process. The structure characterizations of the microdiskettes were investigated in detail by means of XRD, SEM, and HRTEM. The results indicate that the orthorhombic phase of Pb(OH)Br with good crystallinity can be obtained. Meanwhile, controlled experiments show that the concentration of cetyltrimethylammonium bromide (CTAB) play an important role in the formation of the microdiskettes. Moreover, the ultraviolet–visible (UV–vis) absorbance spectra and photoluminescence (PL) microdiskettes show their ultraviolet absorption and green emitting behavior, indicating that the elliptic Pb(OH)Br microdiskettes have great potential to be applied in luminescent and optoelectronic devices.

Microstructure formation mechanism of rapidly solidified ternary Co-Cu-Pb monotectic alloys

The metastable phase separation and rapid solidification of ternary Co-Cu-Pb monotectic alloys have been investigated under free fall condition. With the decrease of droplet diameter, the microstructures of Co51Cu47Pb2 and Co47Cu44Pb9 alloys display a "dendrite→core-shell→dendrite" transformation and a morphology transition from core-shell to homogeneous microstructure, respectively. X-ray diffraction analysis indicates that the solidified microstructures are composed of α(Co), (Cu) and (Pb) phases. α(Co) and (Cu) phases grow mainly in dendritic manner, and (Pb) phase is distributed interdendritically among (Cu) phase. Both experimental results and theoretical calculations reveal that the interfacial energy between (Co)/(Pb) liquid phases is larger than thoses of (Co)/(Cu) and (Cu)/(Pb) phases. The weak wetting ability between (Co) and (Pb) liquids results in the distribution of (Pb) phase inside the Cu-rich zone instead of Co-rich zone. Three possible solidification routes are deduced according to the solidification microstructure, in which the solidification process consists of phase separation L→L1(Cu)+L2(Co), peritectic transformation α(Co)+L→(Cu) and monotectic transformation L(Cu)→S(Cu)+L(Pb).

A new type of antiferrodistortive structure in a double perovskite with Pb

We have found a new structural transition in Pb(2)MnReO(6) at 410 K. Above this temperature, Pb(2)MnReO(6) is cubic with disordered and dynamic atomic displacements manifested in the large thermal parameters of Pb and O atoms. Below 410 K, the antiferrodistortive shift of 2/3 of Pb(2+) cations away from the high-symmetry cubic site produces a new type of monoclinic cell. The unit cell expands at the transition and the heat capacity shows a peak with thermal hysteresis. These features agree with a first order transition. The entropy content of the transition is quite low indicating that the structural disorder has not been completely removed in the low temperature phase. The monoclinic phase of Pb(2)MnReO(6) shows thermally activated conductivity which does not vary when an external magnetic field is applied. A change in the slope of the resistivity curve, observed at the structural phase transition temperature, is related to a slight difference in the activation energy between both phases. It suggests that the condensation of the distortions likely affects the conduction mechanism. The isothermal magnetization measurements reveal the presence of ferromagnetic contributions below 85 K. The ac magnetic susceptibility shows a dynamic peak at 50 K and, in addition, zero-field-cooled and field-cooled magnetization curves diverge strongly below 80 K. These features might be signature of magnetic inhomogeneity. Magnetic loops, obtained at 5 K, do not show saturation in fields up to 9 T. Furthermore, the measured coercivity increases sharply at low temperature indicating an abrupt change in the magnetic anisotropy. We show that all these magnetic properties point out to a ferrimagnetic ordering of Mn and Re atoms in an intermediate valence state.

Dynamic solidification of Sn-38.1% Pb eutectic alloy within ultrasonic field

The dynamic solidification of Sn-38.1% Pb eutectic alloy within an ultrasonic field is investigated at a frequency of 35 kHz. As the sample height H is reduced, the effect of ultrasound on macrosegregation becomes more prominent, and the volume fraction of spherical eutectic cells increases correspondingly. When H equals the wavelength λ in liquid alloy, the introduction of ultrasound enlarges the distribution region of the primary (Sn) phase, but reduces the domains of the Sn-Pb eutectic and primary (Pb) phases. Meanwhile, a “dendritic-equiaxed” structural transition occurs in the primary (Sn) phase, and its grain size is significantly reduced within the ultrasonic field. Once H decreases to λ/2 and λ/4, the ultrasonic field promotes crystal nucleation and suppresses further undercooling of the bulk liquid alloy. Theoretical analyses indicate that the local high pressure induced by the cavitation effect and the stirring effect due to acoustic streaming are the main factors dominating the eutectic growth mechanism during dynamic solidification.

Electrical Properties of Low Temperature Sintered Piezoceramics

In general, commercial PZT piezoceramics are sintered at temperature above 1200°C. Here, one low-temperature sintering technology was developed for PZT piezoceramics by adding perovskite-type ferroelectrics with low sintering temperature, alternative to adding non-piezoelectric low-melting glass or eutectic oxides. Through solid state reaction mechanism, very densified piezoceramics of (Pb0.95Sr0.05)(Zr0.53Ti0.47)O3 with 0.6PbTiO3–0.3Bi(Zn0.5Ti0.5)O3–0.1BiFeO3 as sintering additive were obtained below 1050°C. The phase of (Pb,Bi,Sr)(Zr,Ti,Zn,Fe)O3 solid solution piezoceramics was demonstrated to be single-phased perovskite structure and the measurements of dielectric, ferroelectric and piezoelectric properties showed good piezoelectric performance equivalent to PZT-8.

Phase Transition Near the Morphotropic Phase Boundary in Pb(Zn1/3Nb2/3)O3- PbTiO3

Dielectric constants in Pb(Zn1/3Nb2/3)O3-PbTiO3 were measured under the zero-field heating after a preceding field cooling. It was confirmed that a sharp phase transition between ferroelectric phases in Pb(Zn1/3Nb2/3)O3 appears at 114°C, and the phase boundary connects to the morphotropic phase boundary in the Pb(Zn1/3Nb2/3)O3-PbTiO3 (PZN-PT) solid solution system. A new phase diagram in the poled sample of PZN-PT was proposed in a wider temperature range. It is concluded that the phase transition between ferroelectric phases of PZN is the one between the tetragonal and rhombohedral phases.

Features of the formation of a perovskite phase in thin polycrystalline Pb(Zr,Ti)O3 films

The structure and dielectric properties of thin lead zirconate titanate Pb(Zr,Ti)O3 films grown ex situ on a silicon substrate are studied using various methods (X-ray analysis, raster electron microscopy, atomic-force microscopy, optical microscopy, and dielectric measurements). It is shown that, upon increase in the crystallization temperature, the growth texture of the films changes, leading to a change of their dielectric parameters.

Optical characterization in Pb(Zr1−x Ti x )1−y Nb y O3 ferroelectric ceramic system

In this work, visible photoluminescence was observed at room temperature in a sintered \(\mathrm{Pb}(\mathrm{Zr}_{1-x}\mathrm{Ti}_{x})_{1-y} \mathrm{Nb}_{y}\mathrm{O}_{3}\) perovskite-type structure system, doped with Nb using the next excitation bands 325, 373 and 457 nm. The intensity and energy of such emissions have been studied by changing the Nb concentration (0<y<0.01) and the Ti content (x), with x=0.20,0.40,0.53,0.60 and 0.80, on both sides of the morphotropic phase boundary (MPB) zone. The principal bands become visible at energies of 1.73, 2.56 and 3.35 eV. The results reveal the role of the Nb5+ ion substitutions by Zr4+ or Ti4+ ions and the symmetry presented in the rhombohedral or tetragonal side of the MPB. Raman spectra which are similar for compositions: 20/80, 40/60 and 53/47 (tetragonal phases) show nine bands, centered around 137, 194, 269, 331, 434, 550, 612, 712 and 750 cm−1. The spectra for samples 60/40 and 80/20, rhombohedral phase, show significant differences, only six bands appear, centered around 124, 209, 234, 330, 549 and 682 cm−1. In addition, optical absorption spectroscopy, structural and micro-structural measurements were carried out by using Uv-vis spectroscopy, X-ray diffraction and scanning electron microscopy techniques, respectively. The experimental results of band gap energy, e.g., in our samples are in accordance with the findings by J. Baedi et al. in the calculations of band structure, energy gap and density of states for different phases of Pb(Zr1−xTix)O3 using density functional theory (DFT).

Synthesis of New Cu-based Self-lubricating Composites with Great Mechanical Properties

New copper-based self-lubricating composites consisting of different quantities of graphite are prepared by means of powder metallurgy using a designed atomizing Cu-10Ni-3Sn-3Pb (wt.%) alloy with 0.5 wt.% Y2O3 as the matrix. Microstructures and properties of the composites are studied by scanning electron microscopy, X-ray diffraction, a hardness tester, and a wear tester. The results indicate that the composites sintered at 910°C for 4 h have the best mechanical properties. The composites prepared under such a condition are mainly composed of α-solid solution together with some CuNi 2Sn, Pb, and graphite phases. Here, Ni and Sn play the reinforcing role in the materials by either dissolving into the Cu matrix or forming the second phase with Cu, while Pb and graphite as inclusions act as the lubricating phases. The composites have hardness but deteriorated wear and self-lubricating performance with the increasing graphite content. The composite with 1 wt.% graphite possesses better mechanical and frictional properties, while the composite with 2% graphite possesses better self-lubricating properties. These Cu-based composites with low friction coefficient and enough strength are suitable for the application as surface lubricating film to run under a dry friction condition.

Phase, crystal struture and sintering behavior of shock-synthesized Pb(Zr 0.95Ti 0.05)O 3 powders

With a cylindrical shock-wave-loading technique, the single perovskite-phase Pb(Zr 0.95Ti 0.05)O 3 powders (PZT 95/5) were synthesized by shock-induced chemical reactions in heterogeneous multi-material powder mixtures of Pb 3O 4, ZrO 2 and TiO 2. The phase and crystal structure of as-synthesized powders were characterized by X-ray diffraction (XRD) and fourier transform infrared (FT-IR) analysis. And the microstructure and electrical properties of PZT 95/5 ceramics prepared with as-synthesized PZT powders at different sintering temperature were analyzed. The results showed that the shock-wave-induced a large quantity of lattice defects and distortion of the crystal structure in the shock-synthesized PZT powders, which could enhance the sintering activity. Thus, the optimal density and electrical properties of PZT ceramics prepared with as-synthesized powders could be obtained at a sintering temperature of 1200–1225 °C for 3 h, significantly lower than the sintering temperature of PZT 95/5 ceramics prepared by conventional solid-state reaction.

Field-Induced Phase Transition between Tetragonal and Rhombohedral Phases in Pb(Zn1/3Nb2/3)O3–8%PbTiO3

The field-induced phase transition between the rhombohedral and tetragonal phases was investigated in Pb(Zn1/3Nb2/3)O3–8%PbTiO3 by dielectric constant and electrostriction loop measurements. The temperature-electric-field phase diagram was clarified, and physical properties near the field-induced phase transition were discussed using the Landau-type free energy function.

Characterizations of Thermoplastic Block Elastomers Based on Polybutadiene and ϵ -Caprolactone

A broad series of tri- and multiblock copolymers based on linear and branched oligomers of polybutadiene as central blocks and polycaprolactone (PCL) as block extremities are characterized by SEC, DSC, DMA, Dynamical Rheology and DRX. DSC analyses reveal phase separation between the two amorphous PB and PCL phases. By thermal analysis, the glass transition temperature of PCL is only detected for materials containing at least 80% w/w of PCL. This is attributed to the small length of the polyester blocks for copolymers containing less than 80% w/w of PCL. The increase of fusion heat with increasing PCL content in the copolymers is correlated to the greater ability of PCL chains to rearrange as HTPB amount decrease in the material. Regarding the evolution of the melting temperature of the various copolymers, the characterization by DMA and dynamical rheology confirms the behaviour observed by DSC. Mechanical and rheological properties (i.e., storage modulus and complex viscosities) were studied and reveal that the behavior of the copolymers depends on both the rate of PCL chains and on the nature of the elastomeric block.