Stoichiometric Pb Research Articles

Effect of Lead:Halide Precursor Ratio on the Photoluminescence and Carrier Dynamics of Violet- and Blue-Emitting Lead Halide Perovskite Nanocrystals

Highly luminescent cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals (NCs) are promising materials for a number of optoelectronic applications like LEDs and other display technologies. However, low photoluminescence (PL) quantum yield (QY) of the large-bandgap violet- and blue-emitting CsPbCl3 and CsPb(Cl/Br)3 NCs is an obstacle to the development of blue- and white-emitting LEDs. In this work, we show that these NCs with high PLQY can be obtained directly by employing an appropriate halide precursor and by optimizing the Pb:X precursor ratio. Specifically, employing N-chloro- and N-bromophthalimides as halide precursors and varying the Pb:X precursor ratio, we have obtained stable and highly luminescent (PLQY 80–99%) perovskite NCs emitting in the blue-violet region extending to green by direct synthesis. Time-resolved PL and ultrafast pump–probe studies of these systems reveal the effect of Pb:X precursor ratio on the carrier recombination processes. Rapid carrier trapping is found to be the dominant process that impairs the PLQY of the NCs obtained by using a stoichiometric (1:3) Pb:X precursor ratio. This trapping of carriers is effectively alleviated by using an excess amount of the halide precursor during the preparation of the NCs. The results brighten the potential utility of these high-quality perovskite NCs emitting in the blue-violet region in optical applications.

Rapid synthesis of Pb 5(VO 4) 3I, for the immobilisation of iodine radioisotopes, by microwave dielectric heating

Rapid synthesis of Pb 5(VO 4) 3I, a potential immobilisation host for iodine radioisotopes, was achieved in an open container by microwave dielectric heating of a mixture of PbO, PbI 2, and V 2O 5 at a power of 800 W for 180 s (at 2.45 GHz). The resulting ceramic bodies exhibited a zoned microstructure, differentiated by inter-granular porosity and phase assemblage, as a consequence of the inverse temperature gradient characteristic of microwave dielectric heating. Liquid PbI 2 within the interior of microwave processed ceramics assisted formation of Pb 5(VO 4) 3I, and reduced inter-granular porosity. In contrast, the exterior of microwave processed ceramics comprised poorly sintered Pb 5(VO 4) 3I with the presence of minor reagent relics. Quantitative microanalysis, electron diffraction and Rietveld analysis, confirmed the synthesis of stoichiometric Pb 5(VO 4) 3I within precision. The crystal structure of Pb 5(VO 4) 3I was found to adopt space group P6 3/m with a = 10.4429(3) Å and c = 7.4865(2) Å.

Structure evolution and stoichiometry control of Pb(Zr, Ti)O 3 thick films fabricated by electrospray assisted vapour deposition

Well-crystallized and stoichiometric Pb(Zr, Ti)O 3 (PZT) films, typically ∼5 μm thick, with pure perovskite-type rhombohedral structures have been successfully prepared via an electrospray assisted vapour deposition (ESAVD) method. Control of the deposition temperature within a narrow range of 300–400 °C resulted in films with the most desirable phases. PZT films with close stoichiometric match with the expected composition ratio and uniform element distribution were obtained by adding the appropriate levels of excess Pb in the precursor solutions. The annealed films were uniform, dense, compact and adherent to the substrates. The dielectric constant, ɛ r, and loss tangent, tan δ, of the fabricated PZT films measured at 10 kHz were 442 and 0.09, respectively. The ESAVD deposited PZT films showed a remanent polarization, P r, of 15.3 μC/cm 2 and coercive field, E c, of 86.7 kV/cm. These results demonstrate the clear potential of the ESAVD method as a promising technique for the fabrication of thick PZT films.

Structural properties of [formula omitted] determined from high-resolution synchrotron powder diffraction

We report on the crystallographic structure of the layered compound Pb 3 Mn 7 O 15 . Previous analysis based on laboratory X-ray data at room temperature gave contradictory results in terms of the description of the unit cell. Motivated by recent magnetic bulk measurements of this system [N.V. Volkov, K.A. Sablina, O.A. Bayukov, E.V. Eremin, G.A. Petrakovskii, D.A. Velikanov, A.D. Balaev, A.F. Bovina, P. Boni, E. Clementyev, J. Phys. Condens. Matter 20 (2008) 055217], we re-investigated the chemical structure with high-resolution synchrotron powder diffraction at temperatures between 15 and 295 K. Our results show that the crystal structure of stoichiometric Pb 3 Mn 7 O 15 has a pronounced 2-dimensional character and can be described in the orthorhombic space group Pnma.

Crystal structure of the new compound Pb 3+xSb 3−xS 7−xCl 1+x( x∼0.45): The homologous series Pb (2+2N)(Sb,Pb) (2+2N)S (2+2N)(S,Cl) (4+2N)Cl N and its polychalcogenide derivatives ( N=1–3)

The new chloro-sulfosalt Pb 3+ x Sb 3− x S 7− x Cl 1+ x ( x∼0.45) has been synthesized at 500 °C from a mixture of PbS, PbCl 2 and Sb 2S 3. It crystallizes in the orthorhombic system (space group Pbam), with a=15.194(3) Å, b=23.035(5) Å, c=4.0591(8) Å, V=1420.6 Å 3, Z=4. The crystal structure has been solved by X-ray single-crystal study, with a final R=0.0497. Deviation from stoichiometric Pb 3Sb 3S 7Cl ( x coefficient) follows the substitution rule Sb 3++S 2−→Pb 2++Cl −. Sb and Pb sub-positions within mixed (Sb,Pb) sites are discussed; Pb excess precludes any superstructure along c. A unique pure Cl position is bound only to Pb atoms with a distorted square coordination. The title compound is a rod-type structure derived from the SnS archetype, homeotypic with Pb 6Sb 6S 14(S 3), where the (S 3) 2− trimer is replaced by two Cl −; this substitution is quite isovolumic. Other similar structures are: three polychalcogenides Sr 6Sb 6S 14(S 3), Pb 6Sb 6Se 14(Se 3) and Eu 6Sb 6S 14(S 3); KLa 1.28Bi 3.72S 8 and its Ln isotypes; dadsonite, Pb 23Sb 25S 60Cl. Pb 3+ x Sb 3− x S 7− x Cl 1+ x is the N=2 member of the homologous series Pb (2+2 N )(Sb,Pb) (2+2 N )S (2+2 N )(S,Cl) (4+2 N )Cl N ; the N=1 member corresponds to the previously known ∼Pb 4.3Sb 3.7S 8.7Cl 2.3 compound. Other polychalcogenide derivatives of this homologous series are K 2Pr 2− x Sb 4+ x Se 8(Se 4) and its Ln isotypes ( N=1), as well as SrBiSe 3 ( N=3). Such a comparative modular analysis allowed to propose a structural model for the previous synthetic “Phase Y”, ∼Pb 10Sb 10S 23Cl 4, corresponding to the combined N=(1+2) homolog.

A comparison of the optical properties of amorphous and polycrystalline PZT thin films deposited by the sol–gel method

Stoichiometric Pb(Zr x Ti (1− x) O 3) (PZT) thin films deposited on Si(1 0 0) substrates have been prepared by the sol–gel technique. Two sets of films of amorphous and polycrystalline, containing 20%, 30%, 50%, and 60% Ti, were prepared and investigated. The microstructures and surface morphologies of the films have been studied by X-ray diffraction and atomic force microscopy. The optical properties were studied by spectroscopic ellipsometry (SE) in the UV–visible region. Using a four-phase fitting model, the refractive index n and extinction coefficient k was obtained by analyzing the SE spectra. The optical band gap energies E g for these films were determined under the assumption of a direct band-to-band transition. The results show that the refractive index, extinction coefficient, and band gap energy of the films show a systematic variation with compositions and microstructures. The optical band gap energy of the amorphous PZT films shift to high energy is mainly due to the quantum-size effect.

Effect of heating rate on properties of Pb(Mg 1/3Nb 2/3)O 3 ceramics produced by the reaction-sintering process

Effects of heating rate on properties of stoichiometric Pb(Mg 1/3Nb 2/3)O 3 (PMN) perovskite ceramics produced by the reaction-sintering process are investigated. Without calcination, a mixture of PbO, Nb 2O 5 and Mg(NO 3) 2 was pressed and heated to 1270 °C directly at various rates. Stoichiometric PMN ceramics of 100% perovskite phase are obtained at 5, 10, 20 and 30 °C/min heating rates. Density increases as heating rate increased from 5 to 10 °C/min and reaches a maximum 8.06 g/cm 3 at 10 °C/min. Grains 5.4–7.5 μm in size are obtained at heating rates from 5 to 30 °C/min. K max increases as the rate increases from 5 to 10 °C/min and decreases at higher rates.

Stoichiometric perovskite PMN-PT ceramics produced by reaction-sintering process

Stoichiometric (1 − x)Pb(Mg 1/3Nb 2/3)O 3– xPbTiO 3 (PMN-PT, x=0.05, 0.1) perovskite ceramics produced by reaction-sintering process have been investigated. Without any calcination, a mixture of PbO, Nb 2O 5, TiO 2 and Mg(NO 3) 2 was pressed and sintered directly. Stoichiometric PMN-PT ceramics of 100% perovskite phase were obtained for 2 and 4 h sintering at 1150 to 1250 °C. Density of 8.08 and 8.04 g/cm 3 were obtained in 0.95PMN-0.05PT ceramics sintered at 1250 °C for 2 and 4 h, respectively. For 0.9PMN-0.1PT ceramics, density of 8.07 and 8.03 g/cm 3 were obtained as sintered at 1230 °C for 2 and 4 h, respectively.

Stoichiometric Pb(Mg 1/3Nb 2/3)O 3 perovskite ceramics produced by reaction-sintering process

Stoichiometric lead magnesium niobate, Pb(Mg 1/3Nb 2/3)O 3 (PMN), perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb 2O 5, and Mg(NO 3) 2 was pressed and sintered directly. Stoichiometric PMN ceramics of 100% perovskite phase were obtained for 1, 2, and 4 h sintering at 1250 and 1270 °C. PMN ceramics with density 8.09 g/cm 3 (99.5% of theoretical density 8.13 g/cm 3) and K max 19,900 under 1 kHz were obtained.

Stoichiometric Perovskite Lead Magnesium Niobate Ceramics Produced by Reaction-Sintering Process

Stoichiometric Pb(Mg1/3Nb2/3)O3 perovskite ceramics produced by a reaction-sintering process are investigated. Without calcination, the mixture of PbO, Mg(NO3)2 and Nb2O5 was pressed and sintered directly with and without a 950°C/2 h stage. Stoichiometric PMN ceramics of 100% perovskite phase are obtained after 1200–1270°C sintering with a 950°C/2 h stage. Without the 950°C/2 h stage, 100% perovskite phase PMN ceramics are also obtained after 1 h, 2 h and 4 h sintering at 1250°C and 1270°C. PMN ceramics with density 8.09 g/cm3 and Kmax 19900 under 1 kHz are obtained by a reaction-sintering process.

Stoichiometric Pb(Fe1/2Nb1/2)O3 perovskite ceramics produced by reaction-sintering process

Stoichiometric Pb(Fe1/2Nb1/2)O3 (PFN) perovskite ceramics produced by reaction-sintering process were investigated. Without calcination, a mixture of PbO, Nb2O5, and Fe(NO3)3 was pressed and sintered directly. Stoichiometric PFN ceramics of 100% perovskite phase were obtained for 2 and 4 h sintering at 1120 and 1210 °C. PFN ceramics with density 8.25 g/cm3 were obtained.

Spectroscopic ellipsometry studies of amorphous PZT thin films with various Zr/Ti stoichiometries

Amorphous stoichiometric Pb(Zr x Ti1 − x)O3) (PZT) thin films with various values of x were deposited on Si(100) substrates by the sol-gel technique. The influence of Ti content on the optical properties was studied by spectroscopic ellipsometry (SE) in the UV-visible region. Using a four-phase fitting model, the refractive index n and extinction coefficient k was obtained by analyzing the SE spectra. The optical band gap energies E g for these films were reported under the assumption of a direct band-to-band transition. It has been found that the refractive index, extinction coefficient and band gap energy of the films were functions of the film compositions. The refractive index of the PZT films increases linearly with increasing Ti content. On the other hand, the optical band gap energy of the PZT films decreases with increasing Ti content.

TiO 2-Assisted photocatalysis of lead–EDTA

Several industrial and remedial processes create aqueous wastes containing complexed heavy metal species. TiO 2-assisted photocatalysis was evaluated to address contamination problems from Pb–EDTA at both stoichiometric and non-stoichiometric Pb(II)/EDTA ratios. Pb–EDTA destruction occurred rapidly. At higher pH, lead became adsorbed onto the TiO 2 as complexed intermediates. Continued PCO saw reappearance of the lead in solution, primarily as Pb 2+. Stoichiometric Pb–EDTA studies showed no noticeable pH effects even though Pb–EDTA adsorption depends strongly on pH. This suggests that initial complex adsorption is not required for its destruction and that Pb–EDTA photocatalysis occurs both at the TiO 2 surface and in the aqueous phase. Production of CO 2 and formaldehyde during photocatalysis suggests initial attack at an acetate group on the complex. Acetate and formate were found as minor intermediates. Nitrogen-containing products were ammonium and nitrate. For EDTA>Pb(II) studies, smaller amounts of CO 2 compared with stoichiometric Pb–EDTA were found, suggesting that attack on the acetate group is promoted by lead complexation. Pb(II)>EDTA studies showed decreasing CO 2 production with increasing pH, resulting from a shift in adsorbed Pb–EDTA speciation, or increased adsorption of free lead at higher pH, decreasing the available surface sites for OH · production.

Knudsen cell mass spectrometric investigation of the PbO-ZrO(2)-TiO(2) system.

Knudsen effusion mass spectrometry (KEMS) was used for direct determination of lead oxide activity as a function of temperature in various regions of the PbO-ZrO(2)-TiO(2) system. From the results, the enthalpy, Gibbs free energy and entropy of formation of PbTiO(3) (PT), PbZrO(3) (PZ) and Pb(Zr,Ti)O(3) (PZT) were evaluated. In addition, the single phase widths of Pb(Zr(0.5)Ti(0.5))O(3) and PbTiO(3) perovskite structures were determined at 1100 K. The reaction rate of PZT synthesis in vacuo was followed by direct measurement of the change of PbO activity with time. Lead oxide activity in stoichiometric Pb(Zr(0.5)Ti(0.5))O(3), PbTiO(3) and Pb(0.968)(Zr(0.5)Ti(0.5))O(2.968) (3% lead deficient) at 850 degrees C was found to be 0.40, 0.45 and 0.1, respectively. PZT, PT and PZ powder samples prepared by a solid state procedure were also measured, all revealing lead deficiency. Copyright 1999 John Wiley & Sons, Ltd.

Pb 2 Exchange Isotherms for Zeolite Na-X at pH 5, 6, and 7

Aqueous Pb 2+ exchange into zeolite X powder with unit-cell composition Na 79Si 113Al 79O 384 has been studied at 25°C at pH 5.0, 6.0, and 7.0. The isotherms show that overexchange takes place at all pHs studied and that it increases with increasing pH. There is no plateau at full stoichiometric Pb 2+ exchange at any pH. Pb 2+ and OH − seem to enter the zeolite together to replace Na +.

Temperature dependence of lead loss in r.f. magnetron sputtering of a stoichiometric Pb(Zr,Ti)O 3 target

The temperature dependence of lead loss was studied for r.f. magnetron sputtering of a stoichiometric Pb(Zr,Ti)O 3 target (Zr:Ti ratio of 53:47). Films deposited at 200 °C or below crystallized into perovskite Pb(Zr,Ti)O 3 on receiving an annealing treatment at 600 °C or above. No excess lead was used either during sputtering or during post-deposition annealing. The Pb(Zr,Ti)O 3 films thus prepared are highly ferroelectric with a maximum polarization of 37 μCcm −2, a remanent polarization of 22 μCcm −2, and a coercive field of 40 kVcm −1 measured at 50 Hz. This suggests that lead loss during deposition is negligible for deposition temperatures of 200 °C or below. Films deposited at 500 °C were dielectric as-deposited, and became weakly ferroelectric after being annealed at 800 °C for 1 h. X-ray spectroscopy analysis of the film indicates significant loss of lead at 500 °C. Depositions at 600 °C, however, resulted in thermally stable and dielectric ZrTiO 4 films. The structural and dielectric properties of the films remained unchanged even after annealing at 800 °C for 1 h. X-ray spectroscopy analysis indicates that lead was lost completely during sputtering at 600 °C. Utilizing this temperature dependence of lead loss to control the composition of deposited films, a Pb(Zr,Ti)O 3/ZrTiO 4 heterostructure was also prepared successfully from a single oxide target with a two step, single deposition process.

Oxalate coprecipitation route to the piezoelectric Pb(Zr,Ti)O3 oxide

A homogeneous and stoichiometric Pb(Zr,Ti)O 3 (PZT) fine powder was prepared by thermal decomposition of the metal oxalate precursor formed by the precipitation reaction of the metallic components in aqueous solution with oxalic acid. Theoretical solubility isotherms of metal oxalates were established as a function of the solution pH and the metal ion concentration using thermodynamic equilibrium constants for the corresponding metal salts in aqueous solution. Through the theoretical solubility isotherms, the optimum pH domain for preparing the homogeneous and stoichiometric PZT–oxalate precursor was found to be 3–4. Crystalline PZT with tetragonal symmetry began to form after heating the precursor at 600 °C and a monophasic PZT powder consisting of submicrometer (0.3–0.5 µm) particles with spherical shape could be obtained after calcination at 800 °C for 2 h. The oxalate-derived PZT powder showed a good sinterability even below 1150 °C where the piezoelectric properties were optimized.

Preparation of ferroelectric Pb(Zr0.53Ti0.47)O3thin film on YBa2Cu3O7–δfilm by magnetron sputtering

Abstract We have prepared epitaxial ferroelectric Pb(Zr0.53Ti0.47)O3 /superconductive YBa2Cu3O7–δ heterostructures on single crystalline (100) SrTiO3 by in-situ RF magnetron sputtering from powder targets. The YBCO film was first deposited on 10×10mm (100) SrTiO3 substrate at 700°C. Then the PZT film was sputtered on epitaxial YBCO layer from a stoichiometric Pb(Zr0.53Ti0.47)O3 powder target. Only (00l peaks of PZT film are observed, showing that the PZT film can be epitaxially grown on the YBCO layer using in-situ RF magnetron sputtering from powder targets. A remanent polarization of 10μC/cm2 was obtained from the PZT/YBCO heterostructures. The coercive filed is about 90kV/cm.

Microstructure and properties of lead ferroniobate ceramics (Pb(Fe 0.5Nb 0.5)O 3)

Pure, single phase stoichiometric Pb(Fe 0.5Nb 0.5)O 3 (PFN) powders were successfully formed by molten salt synthesis using a mixture of NaCl and KCl salts. The sinterability and changes in microstructure of these powders, and the dielectric properties of sintered samples, were studied for both pure PFN and PFN with additives such as PbO and Li 2CO 3. The dielectric properties were sensitive to specimen density, the type of additive and the amount of additive. Pure PFN specimens, which were sintered at 1100 °C for 13 h, exhibited high dielectric constant values (12 270 at 1 MHz). PFN ceramics sintered with PbO as an additive showed inferior dielectric properties, although PbO served as a sintering aid and increased the specimen density. The dielectric properties of PFN with Li 2CO 3 additive are promising, because they exhibit both high dielectric constant values (14 000 at 1 MHz) and low values of d.c. conductivity. The improved dielectric properties with the addition of Li 2CO 3 might be attributed to the substitution of Fe by Li.

Molten Salt Synthesis of a Complex Perovskite, Pb(Fe0.5Nb0.5)O3

Pure, single‐phase stoichiometric Pb(Fe0.5Nb0.5)O3 (PFN) powders were successfully formed by molten salt synthesis using mixtures of NaCl and KCl salts. Lower temperatures and shorter times (1/2 h at 800°C) were needed for singlephase PFN formation from molten salts relative to those required for solid‐phase methods (4 h at 1000°C). A systematic study indicating the effects of process parameters, such as temperature, time, and amount of flux with respect to starting oxides, on the PFN formation mechanism and its resulting powder characteristics is reported. The particle size increased with increasing synthesis temperature; the rate of increase was greatest above 900°C, which is close to the melting point of PbO. PFN powders formed by molten salt synthesis are spheroidal, free from aggregates, and sintered to good densities at temperatures as low as 1000°C.