Effect of lead on formation and dielectric tunability of (Pbx,Sr1? x )0.85Bi0.1TiO3 thin films

(Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin films with the perovskite phase structure were prepared on an ITO glass substrate by sol-gel method. X-ray diffraction (XRD), scanning electron microscopy (SEM) and an impedance analyzer were respectively used in order to characterize the phase status, morphology and dielectric properties of the thin films. The results show that during the formation process of (Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin films, the nucleus of the perovskite phase are initially formed and then congregated. These aggregated nucleus are then transformed as the perovskite-phase crystalline in the thin film. Finally, the crystalline phase grows and separates gradually to form the perfect crystalline-phase structure. The content of the perovskite phase formed in the thin film under rapid thermal process (RTP) is more than that formed under traditional heat treatment with kinetic equilibrium. This is due to the high active decomposed ions that form the perovskite phase directly when heat-treated by RTP. The formation of the perovskite phase therefore overcomes a much lower barrier under RTP than that under traditional calcinations. The structure of the perovskite phase has a close relation to the ratio of Pb/Sr in the system because of the radius difference between Pb²⁺ and Sr²⁺. The transformation temperature between the cubic and the tetragonal structures of the perovskite phase increases with increasing Pb²⁺ content because the radius of Pb²⁺ is larger than that of Sr²⁺. It appears at room temperature when the content of Pb²⁺/Sr²⁺ is about 40/60 in the thin film. Meanwhile, the tetragonality of the perovskite phase is increased when Pb²⁺ ions increase due to its high polarization. The higher tunability of the (Pb_x,Sr_1−x )_0.85Bi_0.1TiO₃ thin film is exhibited when the film composition is close to the transformation point between the paraelectric and ferroelectric phases. Pb²⁺ ions show a dominant factor to affect the Curie point of the system and then changing tunability. Translated from Journal of Inorganic Materials, 2006, 21(2): 466–472 [译自: 无机材料学报]     

Structure of Sr1 ? xPbxFeO3 ? δ (0 < x < 0.5) perovskite-like materials

We have synthesized Sr_{1 − x} Pb _x FeO_{3 − δ} (x = 0, 0.05, 0.1, 0.15, 0.2, 0.3, 0.5) perovskite-like materials and studied their structure by X-ray diffraction, M?ssbauer spectroscopy, and electron microscopy. According to the X-ray diffraction data, the Pb solubility limit in the perovskite structure is x ≈ 0.15. The materials with x = 0.05 and 0.1 contained Pb_1.33Sr_0.67Fe₂O₅ inclusions 10–30 nm in size. Using chronopotentiometry and temperature-programmed desorption, we have estimated oxygen mobility in the materials with x = 0.05 and 0.1. The results demonstrate that Pb doping increases oxygen mobility in the strontium-ferrite-based materials.     

X-ray characterisation of chemical solution deposited PbTiO3 films with high Ca doping

Single crystalline phase lead calcium titanate (Pb_1−xCa_xTiO₃) (PCT) thin films, with Ca²⁺ contents between 24 and 50 at.%, have been prepared onto Pt/(1 0 0)MgO by chemical solution deposition and rapid thermal processing. The sol-gel process used enables the synthesis of air-stable and precipitate-free solutions with high Ca²⁺ contents (up to 50 at.% of substitution of Pb²⁺ by Ca²⁺ in the PbTiO₃ perovskite has been tested). Structure and texture of the crystalline films have been determined by X-ray diffraction (XRD), using the Bragg-Brentano geometry. Strain of the films structure has been calculated by the variance method using the 1 1 1 perovskite peak of the grazing incidence XRD patterns. Data obtained by XRD and dielectric properties measured in the PCT films are compared with those reported for bulk ceramics.     

Structural characterization of 0.5PbMg1/3Nb2/3O3-0.5BaxPb(1−x)TiO3 powders

The present work reports the effects caused by barium on phase formation, morphology and sintering of lead magnesium niobate-lead titanate (PMN-50PT). Ab initio study of 0.5Pb(Mg_1/3Nb_2/3)O₃-0.5(Ba_xPb_(1−x)TiO₃) ceramic powders, with x = 0, 0.20, and 0.40 was proposed, considering that the partial substitution of lead by barium can reestablish the equilibrium of monoclinic-tetragonal phases in the system. It was verified that even for 40 mol% of barium, it was possible to obtain pyrochlore-free PMN-PT powders. The increase of the lattice parameters of PMN-PT doped-powders confirmed dopant incorporation into the perovskite phase. The presence of barium improved the reactivity of the powders, with an average particle size of 120 nm for 40 mol% of barium against 167 nm for the pure sample. Although high barium content (40 mol%) was deleterious for a dense ceramic, contents up to 20 mol% allowed 95% density when sintered at 1100 °C for 4 h.     

Crystal Chemistry of Lead Titanate in Relation to Its Electrical Properties

The origin of the discrepancy between the measured average parameter of the perovskite unit cell of PbTiO₃and the unit-cell parameter calculated for an ideal perovskite structure is analyzed with the use of extended x-ray absorption fine structure spectroscopy data, which demonstrate that PbTiO₃contains Pb⁴⁺ions. The amount of Pb⁴⁺depends on the preparation conditions and may attain 6 at. %. Assumption is made that the presence of crystallographic shear planes allows a fraction of the Pb²⁺ions to occupy octahedral sites near the shear planes. The maximum content of Pb²⁺on the B site is 2.5 at. %. The formula proposed for the cation composition of imperfect lead titanate differs from the ideal formula Pb²⁺Ti⁴⁺O₃and indicates that lead titanate can be thought of as an internal solid solution. It is shown that the composition of lead titanate influences its electrical properties: /₀increases with Pb⁴⁺concentration and exceeds that in single crystals by an order of magnitude.     

Effect of excess Pb in PbTiO<Subscript>3</Subscript> precursors on ferroelectric and fatigue property of sol–gel derived PbTiO<Subscript>3</Subscript>/PbZr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>O<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> thin films

A series of Pb_(1+x)TiO₃/PbZr_0.3Ti_0.7O₃/Pb_(1+x)TiO₃ (PTO/PZT/PTO) and PbZr_0.3Ti_0.7O₃ (PZT) thin films were prepared by a sol–gel method. Different excess Pb content (x) (x = 0, 0.05, 0.10, 0.15, 0.20) were added to the PbTiO₃ (PTO) precursors to investigate their effect on ferroelectric and fatigue properties of the PTO/PZT/PTO thin films. X-ray diffraction results show that the crystallization behavior of the PTO/PZT/PTO thin films is greatly affected by the excess Pb content (x) in PTO precursors. Topographic images show that the PTO/PZT/PTO thin films with excess Pb content x = 0.10 appears the densest and the most uniform grain size surface morphology. The ferroelectric and fatigue properties of the films correlate straightforwardly to the crystallization behaviors and excess Pb content (x) in the PTO precursors. The excess Pb content (x) in the PTO layers which acts as a nucleation site or seeding layer for PZT films affects the crystallization of the PTO layer and ultimately affects the perovskite phase formation of the PZT films. With the proper excess Pb content (x = 0.10–0.15) in the PTO precursors, the pure perovskite structure PTO/PZT/PTO thin films, with dense, void-free, and uniform fine grain size are obtained, and a well-saturated hysteresis loop with higher remnant polarization is achieved. Using an appropriate Pb content, the fatigue has been avoided by controlling the inter-diffusion and surface volatilization.     

Pb and In Codeposition in the Vacuum Growth of PbTe<In> Films on Si Substrates

Pb_{1 – x} In _x melts were proposed to be used as In vapor sources, in combination with separate Pb and Te sources, in depositing PbTe films onto Si substrates by a modified hot-wall method. Under the assumption that the presence of Pb in Pb_{1 – x} In _x melts may raise the In partial pressure, the vaporization behavior of Pb_{1 – x} In _x (0.05 x 0.70) was studied between 900 and 1200 K in the reaction chamber of the deposition unit. Using electron probe x-ray microanalysis and x-ray diffraction, all the deposited films were shown to contain In. The In content of the Pb_{1 – y} In _y deposits varied in the range 0.002 <y < 0.07 and increased with increasing In concentration in the Pb_{1 – x} In _x melt and with increasing vapor source temperature. The vapor over molten Pb_{1 – x} In _x was shown to exhibit a positive deviation from ideality.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

Crystal chemistry of REVO3 phases (RE = La-Lu,Y)

All REVO₃ phases have been prepared and characterized by x-ray powder diffraction for symmetry and unit cell parameters. LaVO₃ and CeVO₃ have tetragonal variations of the perovskite structure while all remaining REVO₃ phases are orthorhombic and isostructural with GdFeO₃. The variation of cell parameters with RE³⁺ ionic radius shows a steady contraction with decreasing radius for a_o, c_o and V while b_o goes through a maximum.     

Crystal structure of (Sr,Ba)Bi2Ta2O9

The crystal structure of (Sr_0.9Ba_0.1)Bi₂Ta₂O₉ has been refined to elucidate the nature of the lower phase transition observed in even-layered members of the bismuth titanate family. Least squares analysis based on x-ray and neutron diffraction intensities led to an R-factor of 0.13 for 1135 reflections. Bismuth strontium barium tantalate is orthorhombic, space group A2₁am, with a = 5.504, b = 5.488, $\text{c}\text{= 25.06}\text{A}\text{?}$, and Z = 4. Near the lower transition, five short Bi-O bonds are retained in the bismuth oxide layer, but distortions in the perovskite are reduced considerably, with the Ta ion displaced just 0.05Å from the center of the octahedron.     

Solid state synthesis and structural refinement of polycrystalline La<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Ca<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> ceramic powder

Perovskite structure based ceramic precursors have a characteristic property of substitution in the “A” site of the ABO₃ structure. This makes them a potential material for nuclear waste management in synthetic rock (SYNROC) technology. In order to simulate the mechanism of rare earth fixation in perovskite, La_x Ca_1−xTiO₃ (wherex = 0.05) has been synthesized through ceramic route by taking calculated quantities of oxides of Ca, Ti and La as starting materials. Solid state synthesis has been carried out by repeated pelletizing and sintering the finely powdered oxide mixture in a muffle furnace at 1050°C. The ceramic phase has been characterized by its powder diffraction pattern. Step analysis data has been used to determine the structure of solid solution of lanthanum substituted calcium titanate. The SEM and EDAX analyses also confirm that the CaTiO₃ can act as a host for lanthanum. X-ray data has been interpreted using CRYSFIRE and POWDERCELL softwares. Theh, k, l values for different lattice planes have been generated from the experimental data. The lanthanum substituted perovskite crystallizes in orthorhombic symmetry with space groupP n m a (#62). Following unit cell parameters have been calculated:a = 5.410,b = 7.631,c = 5.382. The calculated and observed values of corresponding intensities, 2θ, and density show good agreement. GSAS based calculation for bond distances Ti-O, Ca-O, La-O and bond angles Ti-O-Ca, Ca-O-Ca, La-O-Ti have been reported.     

Growth of Ferroelectric Pb(Ta1 – xNbx)2O6 Single Crystals

The liquidus relations in the Pb₂V₂O₇–PbNb₂O₆–PbTa₂O₆ system were studied by direct visual observation of melting and x-ray diffraction analysis. Pb(Ta_{1 – x} Nb _x )₂O₆ crystals, both ferroelectric (x= 0.3, 0.5, 0.7; tetragonal potassium tungsten bronze structure type) and nonferroelectric (rhombohedral structure), were grown by precipitation from Pb₂V₂O₇ fluxes. The Curie temperature and peak permittivity of the crystals were found to increase systematically with Nb content.     

Matrix-inducing synthesis and luminescence of microcrystalline red phosphors YVO4:Pb2+,Eu3+ derived from the in situ coprecipitation of hybrid precursors

Using rare-earth coordination polymers with o-hydroxylbenzoate as a precursor, composing with polyvinyl alcohol as a dispersing medium, a novel red-emitting material of YVO₄:xPb²⁺, yEu³⁺ (x=0, 1.0, 1.2, 1.5, 1.8, 2.0, and 5.0 mol %; y=5 mol %) was synthesized by an in situ coprecipitation process. Its microstructure and micromorphology have been analyzed by x-ray powder diffraction and scanning electronic microscopy, which indicates that there exist some novel cobblestone-like microcrystalline particles. With Pb²⁺ as a sensitizer, these materials all exhibit strong red emission near 618 nm due to the ⁵ D ₀ → ⁷ F ₂ transition of Eu³⁺ ions. At x=1.5, YVO₄:Pb²⁺, Eu³⁺ shows the strongest emission intensity, which indicates an efficient energy transfer from Pb²⁺ to Eu³⁺. The text was submitted by the authors in English.     

Stabilization of Low-Temperature SnS by Rare-Earth Doping

Rare-earth-doped SnS was studied by x-ray diffraction. (SnS)_{1 – x} (LnS) _x (Ln = Nd, Sm, Gd; x= 0.001, 0.002) crystals were found to have an orthorhombic structure in the temperature range 300–850 K.     

Lead-strontium titanate glass ceramics: II-dielectric behaviour

Dielectric properties of glass ceramic samples prepared in the system [(Pb_1-xSr_x)O.TiO₂)]- [2SiO₂.B₂O₃]-[K₂O]-[BaO] have been studied. Dielectric constant vs temperature plots of lead rich glass ceramics samples show a peak similar to Curie peak in case of ceramic lead strontium titanate. The Curie temperature of tetragonal crystalline phase of various glass ceramics has been found to decrease with Pb/Sr ratio in the initial glass. This complements X-ray diffraction (XRD) studies carried out previously to establish that the crystallites in various glass ceramic samples are (Pb_1−xSr_x)TiO₃ solid solutions.     

The formation of zirconium tungsten bronzes of the perovskite type

The oxygen rich corner of the ZrO₂-WO₃-WO₂ system has been studied by means of x-ray powder diffraction and electron microscopy at room temperature of specimens quenched from the preparation temperatures of 1000°C and 1100°C. Zirconium tungsten bronzes of formula Zr_xWO₃ are formed for 0<x<0.075. The symmetry of the unit cell increases with rising zirconium content x from monoclinic through orthorhombic to tetragonal (pseudocubic) at approximate x-values of 0.027 and 0.047, respectively. The zirconium atoms enter the empty cages in the tungsten trioxide structure in the same manner as for tungsten bronzes of the perovskite type. No evidence was observed for the formation of any crystallographic shear planes in these bronzes.     

Lead nitroprusside: A new precursor for the synthesis of the multiferroic Pb2Fe2O5, an anion-deficient perovskite

In order to investigate the formation of multiferroic oxide Pb₂Fe₂O₅, the thermal decomposition of Pb[Fe(CN)₅NO] has been studied. The complex precursor and the thermal decomposition products were characterized by IR and Raman spectroscopy, thermal analysis, powder X-ray diffraction (PXRD), scanning electron microscopy and magnetic measurements. The crystal structure of Pb[Fe(CN)₅NO] was refined by Rietveld analysis. It crystallizes in the orthorhombic system, space group Pnma. The thermal decomposition in air produces highly pure Pb₂Fe₂O₅ as final product. This oxide is an anion deficient perovskite with an incommensurate superstructure. The magnetic measurements confirm that Pb₂Fe₂O₅ shows a weak ferromagnetic signal probably due to disorder in the perfect antiferromagnetic structure or spin canting. The estimated ordering temperature from the fit of a phenomenological model was 520 K. The SEM images reveal that the thermal decomposition of Pb[Fe(CN)₅NO] produces Pb₂Fe₂O₅ with small particle size.     

Effect of Trivalent Ion Substitution on the Physical Properties of M-Type Hexagonal Ferrites

Aluminum-substituted barium hexagonal ferrite particles BaAl _x Fe_12-x O₁₉ with 0 ≤ x ≤ 3.5 have been prepared by solid state reaction method. The qualitative phase analysis of studied powder samples and the morphology of powders after milling were determined using the x-ray diffraction method and scanning electron microscopy, respectively. The barium hexagonal ferrite phase appeared to be the main component of the samples. The crystal size of BaFe₁₂O₁₉ phase is above 25 nm. The scanning electron microscopy images showed irregular shape and size of powder particles. According to the analytical method findings, the type of crystal lattice was confirmed to be hexagonal and the parameters of unit cell volume and x-ray density were determined. It is shown that such parameters decrease with increasing Al substitution from 699.019 to 696.702 Å³ and 5.258 to 4.828 gm/Cm³, respectively. The values of lattice parameters, grain size, microstrain, and dislocation density of all samples were calculated. The c/a value obtained from the x-ray indicates that notable changes of the atomic lattice anisotropy were induced by the Al-substitution and preheat treatments. Characteristics such as the interchain distance and interplanar distance parameter, which were obtained in the analytical method calculations, decrease with increasing Al substitution, in addition to the fact that they are related to the binding energy.     

Control of the structure,morphology and dielectric properties of bismuth titanate ceramics by praseodymium substitution using an intermediate fuel agent-assisted self-combustion synthesis

The volatilization of bismuth (Bi) species and bismuth oxide (Bi₂O₃) leads to the presence of the oxygen vacancies (V _O⁰⁰) and consequently restrains the properties of bismuth titanate (BIT; Bi₄Ti₃O₁₂). This report presents the incorporation of different atomic ratios of praseodymium ion (Pr³⁺: x = 0, 0.2, 0.4, 0.6, 0.8 and 1.0) into the BIT (Bi_4−x Pr _x Ti₃O₁₂) ceramics through an intermediate fuel agent-assisted self-combustion synthesis (IFSC). X-ray diffraction and Raman spectroscopy results revealed that some of bismuth ion (Bi³⁺) in the pseudo-perovskite layer containing Ti–O octahedra was substituted by Pr³⁺ ion. The substitution by ion with a smaller ionic radius caused the structure distortion and consequently resulted in the phase transformation from an orthorhombic symmetry to a tetragonal symmetry. Besides, it suppressed the volatilization of Bi and Bi₂O₃ and increased the stability of metal–oxygen octahedra in the BIT. These play a crucial role to control the crystal growth, as well as limit the V _O⁰⁰. Dense ceramic with a relative density up to 96.2% was obtained by incorporating Pr³⁺ with atomic ratio of 1.0. It exhibited high dielectric constant as 908.19 and low dissipation factor as 0.0011. The results address the possibility to control the structure, morphology and dielectric properties of BIT ceramic by incorporating Pr³⁺ ion through IFSC.