Conductivity and Structural Investigations in Lacunary Pb6Ca2Li2(PO4)6 Apatite

Prismatic crystals of Pb₆Li₂Ca₂(PO₄)₆ were obtained by solid-state reaction. They were characterized by IR spectroscopy and chemical analyses. The structure as determined by X-ray diffraction study on single crystal revealed that the compound is isostructural to the hexagonal phase Pb₈Na₂(PO₄)₆. Crystal data for Pb₆Li₂Ca₂(PO₄)₆: space group P63/m (No. 176), a=b=9.6790(15) Å, c=7.1130(7), Z=1, R=0.039. In the compound, lithium was found to preferentially occupy the site (I) and the structure is stabilized by interactions between electron lone pairs of lead (II) ions. Electrical conductivity measured in a wide range of temperature is governed by a hopping mechanism of Li ions in tunnels.     

The enhancement mechanism of dielectric properties of Pb(Zr,Ti)O3 via (Mg2+,Sb3+) incorporation for supercapacitors

Due to the extraordinary versatility of the perovskite structure in accommodating different dopant ions in its structure, in recent years a huge number of multifunctional perovskite materials have been developed. In this work we aim to obtain high temperature-stable and huge dielectric constant materials for supercapacitors by doping divalent Mg²⁺ and trivalent Sb³⁺ ions into the octahedral sites, and divalent Sr²⁺ ions into the dodecahedral sites of lead zirconate-titanate perovskite. The resulting (Pb_0.95Sr_0.05)(Zr_0.425Ti_0.45Mg_0.042Sb_0.083)O_3-δ is examined by X-ray diffraction, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), dielectric spectroscopy (DS) and resonance dielectric spectroscopy (RDS) in order to correlate composition, local structure, ion valence and chemical environment of the doped material with the dielectric properties. HRTEM evidences that a composite structure, with co-existent ferroelectric domains and relaxor nanodomains, is formed by doping. XPS shows that Sb³⁺ and Mg²⁺ substitute for the Ti⁴⁺/Zr⁴⁺ ions, pointing to these strong defects as the main cause for the appearance of the relaxor phase. DS and RDS found that the ferroelectric lead zirconate-titanate transforms into a re-entrant relaxor-ferroelectric composite with a huge dielectric constant of about 10⁴ which remains stable (within ±10%) in the high temperature range up to 250 °C, pointing to this mechanism of relaxor phase re-entrance below the normal ferroelectric phase transition, as being responsible for the enhancement.     

Oxidation of toluene on Bi-doped PbO<Subscript>2</Subscript> studied by electrochemical impedance spectroscopy and UV spectrophotometry

Oxidation of organics in the potential region of O₂ evolution is supposed to proceed through the oxidation of water to hydroxyl radicals, which then may either be further oxidized to give molecular oxygen or interact with organic molecules in an oxygen transfer reaction. Therefore, the electrode material must ensure (1) the preferential adsorption of the organic compound, (2) the production of adsorbed hydroxyl radicals able to react with this compound in a selective oxidation reaction (with as little as possible oxygen evolution), and (3) a long-term stability. In the present paper, the oxidative decomposition of toluene in sulfuric acid solution on PbO₂ coatings deposited on Ti substrate from acidic nitrate + fluoride baths containing Pb²⁺ and Bi³⁺ is investigated by voltammetry, electrochemical impedance spectroscopy, and UV spectrophotometry. The chemical composition and structure of the catalytic coatings is characterized with X-ray photoelectron spectroscopy and X-ray diffraction. The catalytic activity is estimated both from current density vs potential and polarization resistance vs potential plots using measurements on the same electrodes in sulfuric acid without toluene to eliminate the oxygen evolution reaction that proceeds in parallel to the oxidation of toluene. A skeletal reaction mechanism of the process is proposed to account for the steady-state and transient response of the catalytic electrodes during oxidation of toluene.     

Crystal Structure,Dielectric Characteristics and Conduction Mechanism of a New Hybrid Material,Tetra(Phenylpiperazinium) Decachlorotriplumbate(II)

Monocrystalline (C₁₀H₁₅N₂)₄Pb₃Cl₁₀ was obtained via an aqueous solution reaction and characterized by single-crystal X-ray diffraction technique, elemental analyses, IR spectroscopy, UV–Vis spectrum, photoluminescence properties and thermal analysis. Structural characterization reveals that the title compound is built from [Pb₃Cl₁₀]^4? units sharing Cl2 atom to form 2-D [Pb₃Cl₁₀] _n ^4n? layers, these anions are linked to the organic cations via N–H···Cl and C–H···Cl hydrogen bonding. Moreover, dielectric relaxation spectroscopy has also been determined to show different molecular motions. Measurements of AC conductivity as a function of frequency at different temperatures indicated the hopping conduction mechanism.     

Mechanochemical synthesis,structure and properties of lead containing alkaline earth metal fluoride solid solutions MxPb1-xF2 (M = Ca,Sr, Ba)

The paper deals with the mechanochemical synthesis of lead containing alkaline earth metal fluoride solid solutions M_xPb_1-xF₂ (M = Ca, Sr, Ba) by high-energy ball milling. Several metal precursors and fluorinating agents were tested for synthesizing M_0.5Pb_0.5F₂. Metal acetates and ammonium fluoride as precursors show the most promising results and were therefore used for the formation of M_xPb_1-xF₂ with different metal cationic ratios. The characterization of the local fluorine coordination and the crystal structure was performed by ¹⁹F MAS NMR spectroscopy and X-ray diffraction. Additional calculations of ¹⁹F chemical shifts using the superposition model allow a deeper insight into the local structure of the compounds. The fluoride ion conductivity was followed by temperature dependent DC conductivity measurements. Significantly higher conductivities were found in comparison with those of the corresponding binary fluorides. The highest values were observed for samples with high lead content M_0.25Pb_0.75F₂, bearing in mind the much higher conductivity of PbF₂ compared to MF₂.     

Adsorption of Pb(2+) ions on nanosized gamma-Fe(2)O(3): formation of surface ternary complexes on ligand complexation

Adsorption of Pb²⁺ ions on the combustion derived nanosized γ-Fe₂O₃ and its thiourea complex composite is reported. The adsorbents upon adsorption of Pb²⁺ ions are characterised by X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis and infrared spectroscopy techniques. The eluent is characterised by atomic absorption spectroscopy for the estimation of Pb²⁺ ions. The reduction in the amount of lead after adsorption was estimated to be around 50% in case of complex composite adsorbent and around 15% in case of the γ-Fe₂O₃ adsorbents. Orthorhombic PbSO₄ precipitated out from the eluent and is reported with a model reaction. Adsorption of lead onto the complex composite is explained through the formation of a surface tertiary complex. The advantage of employing a thiourea-γ-Fe₂O₃ complex composite as solid adsorbent for the adsorption of heavy metal pollutants is envisaged in the present investigation.     

In situ synthesis of MnO<Subscript>2</Subscript>-loaded biocomposite based on microcrystalline cellulose for Pb<Superscript>2+</Superscript> removal from wastewater

We fabricated a new MnO₂-loaded biocomposite based on microcrystalline cellulose (MCC–MnO₂) by an in situ synthesis method and investigated its adsorption behavior and mechanism for Pb²⁺ removal from aqueous medium. As-prepared MCC–MnO₂ was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), Fourier-transform infrared (FTIR) spectroscopy, and X-ray diffraction (XRD) analyses. The effects of pH value, initial Pb²⁺ concentration, contact time, and solution temperature on the uptake of Pb²⁺ onto MCC–MnO₂ were investigated using a batch system. Adsorption equilibrium could be achieved in 3 h for various studied initial concentrations, and a pseudo-second-order model could fit the adsorption behavior well. The equilibrium data could be well described by the Langmuir isotherm model, and the maximum monolayer adsorption capacity of MCC–MnO₂ (with 7.98% MnO₂ loading) for Pb²⁺ was estimated to be 247.5 mg/g at 313 K. Thermodynamic studies indicated a spontaneous and endothermic adsorption process. X-ray photoelectron spectroscopy (XPS) was used to analyze the adsorption mechanism, revealing that the chemical speciation of Pb²⁺ on MCC–MnO₂ was similar to the compound PbO. Moreover, no variations in the valence of Mn were observed after adsorbing Pb²⁺. The regeneration study showed that the adsorption capacity retained about 89.6% of its initial value at the fifth sequential regeneration cycle, indicating that this material is an efficient and renewable hybrid adsorbent for Pb²⁺ removal.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A Raman spectroscopic study

The minerals mimetite Pb₅(AsO₄)₃Cl, arsenian pyromorphite Pb₅(PO₄,AsO₄)₃Cl and hedyphane Pb₃Ca₂(AsO₄)₃Cl have been studied by Raman spectroscopy complimented with infrared spectroscopy. Mimetite is characterised by a band at 812–3 cm⁻¹ attributed to the A_g mode. For the arsenian pyromorphite this band is observed at 818 cm⁻¹ and for hedyphane at 819 cm⁻¹. For mimetite and hedyphane bands at 788 and 765 cm⁻¹ are attributed to A_u and E_1u vibrational modes and are both Raman and infrared active. For the arsenian pyromorphite, Raman bands at 917–1014 cm⁻¹ are attributed to phosphate stretching vibrations. Raman spectroscopy clearly identifies bands attributable to isomorphous substitution of arsenate by phosphate. The observation of low intensity bands in the 3200–3550 cm⁻¹ region are assigned to adsorbed water and OH units, thus indicating some replacement of chloride ions with hydroxyl ions.     

Vibrational spectroscopic study of the antimonate mineral bindheimite Pb2Sb2O6(O,OH)

Raman spectroscopy complimented with infrared spectroscopy has been used to characterise the antimonate mineral bindheimite Pb₂Sb₂O₆(O,OH). The mineral is characterised by an intense Raman band at 656 cm⁻¹ assigned to SbO stretching vibrations. Other lower intensity bands at 664, 749 and 814 cm⁻¹ are also assigned to stretching vibrations. This observation suggests the non-equivalence of SbO units in the structure. Low intensity Raman bands at 293, 312 and 328 cm⁻¹ are assigned to the OSbO bending vibrations. Infrared bands at 979, 1008, 1037 and 1058 cm⁻¹ may be assigned to δOH deformation modes of SbOH units. Infrared bands at 1603 and 1640 cm⁻¹ are assigned to water bending vibrations, suggesting that water is involved in the bindheimite structure. Broad infrared bands centred upon 3250 cm⁻¹ supports this concept. Thus the true formula of bindheimite is questioned and probably should be written as Pb₂Sb₂O₆(O,OH,H₂O).     

Uranium's Valency in U3S5

U₃S₅ has been prepared by chemical transport reaction and investigated using X-ray powder diffraction, FTIR spectroscopy, electrical resistivity measurements, and X-ray photoelectron spectroscopy. U₃S₅ is a semiconductor with a thermal band gap E_g=78.1(4) meV (298 K<T<50 K), which closes gradually to 3.4(4) meV for T<25 K. Photoelectron spectroscopy on single crystals of U₃S₅ and β-US₂ suggest a mixed valency of uranium in U₃S₅. Physical and structural data are consistent with a mixed-valent model (U³⁺)₂U⁴⁺ (S²⁻)₅. A brief survey of literature data on crystal structure and physical properties of uranium sulfides and selenides is given.     

Synthesis,phase formation,and thermal expansion of sulfate phosphates with the NaZr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structure

The NaFeZr(PO₄)₂SO₄ and Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 sulfate phosphates with the NaZr₂(PO₄)₃ (NZP) structure were synthesized and studied using X-ray diffraction, electron microprobe analysis, IR spectroscopy, and simultaneous differential thermal and thermogravimetric analysis. The phase formation and thermal stability of the compounds were studied by powder X-ray diffraction and DTA–TG. The Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 structure was refined by full-profile analysis. The structure framework is composed of randomly occupied (Fe,Zr)O₆ octahedra and (P,S)O₄ tetrahedra; the Pb²⁺ ions occupy extra-framework sites. The thermal expansion of Pb_2/3FeZr(PO₄)_7/3(SO₄)_2/3 in the temperature range from–120 to 200°C was studied by temperature X-ray diffraction. In terms of the average linear coefficient of thermal expansion (α_av = 1.7 × 10^–6°C^–1), this compound can be classified as having low expansion. The combination of different tetrahedral anions (a phosphorus and a smaller sulfur one) in the NZP resulted in a decrease in the framework size and cavities and enabled the preparation of low-expansion sulfate phosphate with a smaller extra-framework cation (cheap Pb) instead of larger cations (Cs, Ba, Sr) used most often in the monoanionic phosphates.     

Analysis of the electronic structure of Hf(Si0.5As0.5)As by X-ray photoelectron and photoemission spectroscopy

The ternary hafnium silicon arsenide, Hf(Si_xAs_1−x)As, has been synthesized with a phase width of 0.5?x?0.7. Single-crystal X-ray diffraction studies on Hf(Si_0.5As_0.5)As showed that it adopts the ZrSiS-type structure (Pearson symbol tP6, space group P4/nmm, Z=2, a=3.6410(5) Å, c=8.155(1) Å). Physical property measurements indicated that it is metallic and Pauli paramagnetic. The electronic structure of Hf(Si_0.5As_0.5)As was investigated by examining plate-shaped crystals with laboratory-based X-ray photoelectron spectroscopy (XPS) and synchrotron radiation photoemission spectroscopy (PES). The Si 2p and As 3d XPS binding energies were consistent with assignments of anionic Si¹⁻ and As^1-. However, the Hf charge could not be determined by analysis of the Hf 4f binding energy because of electron delocalization in the 5d band. To examine these charge assignments further, the valence band spectrum obtained by XPS and PES was interpreted with the aid of TB-LMTO band structure calculations. By collecting the PES spectra at different excitation energies to vary the photoionization cross-sections, the contributions from different elements to the valence band spectrum could be isolated. Fitting the XPS valence band spectrum to these elemental components resulted in charges that confirm that the formulation of the product is Hf²⁺[(Si_0.5As_0.5)As]²⁻.     

Synthesis, crystal structure and optical properties of the new lead fluoride borate—Pb2BO3F

A new compound, Pb₂BO₃F, has been grown by high temperature solution method from the PbO–PbF₂–B₂O₃ system for the first time. The crystal structure of this compound has been identified by single crystal X-ray diffraction analysis. It crystallizes in the hexagonal system, space group P6₃/m (No. 176) with unit-cell parameters a=7.2460(3) Å, c=14.5521(17) Å, Z=6, V=661.69(9) ų. Its structure was solved by the direct methods and refined to R₁=0.0163 and wR₂=0.0367. The structure of Pb₂BO₃F consists of the distorted PbO₃F₂ groups and BO₃ triangles, which are all symmetric with each other in the gestalt structure to the extent that the Pb₂BO₃F compound crystallizes in the symmetric space group. The powder X-ray diffraction pattern of the Pb₂BO₃F has been measured. The BO₃ functional groups presented in the sample were identified by FTIR spectrum. The DTA curve of Pb₂BO₃F suggests that Pb₂BO₃F melts congruently at 448 °C.     

A three‐dimensional metal–organic polymer: poly[bis(μ2‐pyrimidine‐2‐thiolato‐κ4N1,S:S,N3)lead(II)]

The title compound, [Pb(C₄H₃N₂S)₂]_n, was prepared by the reaction of [Pb(OAc)₂]·3H₂O (OAc is acetate) with pyrimidine‐2‐thione in the presence of triethylamine in methanol. In the crystal structure, the Pb^II atom has an N₄S₄ coordination environment with four ligands coordinated by N‐ and S‐donor atoms. This compound shows that the pyrimidine‐2‐thiolate anion can lead to a three‐dimensional network when the coordination number of the metal ion can be higher than 6, as is the case with the Pb^II ion. This compound presents only covalent bonds, showing that despite the possibility of the hemidirected geometries of Pb^II, the eight‐coordinated ion does not allow the formation of an isolated molecular structure with pyrimidine‐2‐thiolate as the ligand.     

The polar mixed-valent lanthanum iron(II, III) sulfide La3Fe2−δS7: Synthesis, crystal and electronic structure, Fe Mößbauer spectra, magnetic susceptibility and electrical resistivity

La₃Fe_2−δS₇ (δ=0.042(6)) was synthesized through a reaction of the elements in a LiCl/KCl flux at 970 K, and its structure was determined by single-crystal X-ray diffraction. The compound crystallizes in the polar hexagonal space group P6₃ with a=10.1906(6), c=5.9543(4) Å and Z=2, and adopts the Ce₆Al_10/3S₁₄ structure type. The structure contains both octahedral and tetrahedral iron sites: one-dimensional rods of face-sharing FeS₆ octahedra run along the 6₃ screw axis of the cell; FeS₄ tetrahedra, all pointing in the same direction, are stacked along the threefold rotation axes. The iron-centered polyhedra are linked by lanthanum atoms, which are coordinated by [7+1] sulfur atoms in a bicapped trigonal prismatic arrangement. ⁵⁷Fe Mößbauer spectroscopy confirms that Fe^III and Fe^II cations occupy the tetrahedral and octahedral iron sites, respectively. Magnetic susceptibility data indicate an antiferromagnetic transition at T_N≈155 K. Density functional band structure calculations within the local density approximation reveal two covalent Fe-S subsystems within the compound that mix only weakly. A large anisotropy is indicated by bands that disperse predominantly along the hexagonal axis. The electronic band structure suggests pseudo-one-dimensional metallic conductivity along the rods of face-sharing FeS₆ octahedra. However, due to the defects on the Fe^II positions, La₃Fe_2−δS₇ shows an activated conducting behavior.     

Synthesis and structure investigation of the Pb3V(PO4)3 eulytite

Lead vanadium phosphate Pb₃V(PO₄)₃ was synthesized by solid state reaction and characterized by X-ray single crystal and powder diffraction, electron microscopy, and magnetic susceptibility measurements. The crystal structure model of Pb₃V(PO₄)₃ was refined using X-ray single crystal data (a=10.127(1)Å, S.G. Z=4). The compound has an eulytite-like structure and its average structure model may be presented as a three-dimensional network formed by strongly distorted mixed (Pb/V^III) metal-oxygen octahedra connected by edge sharing and forming corrugated chains. The octahedra are additionally linked by tetrahedral phosphate groups via corner sharing. Lead and vanadium atoms randomly occupy two close positions in the octahedra. The electron microscopy study revealed the presence of a rhombohedral superstructure with and indicating ordering in the structure. The same type of superstructure was found by us for two another lead-containing eulytite Pb₃Fe(PO₄)₃ where Fe⁺³ has an ionic radius close to that of V⁺³. Magnetic susceptibility measurements revealed Curie-Weiss behavior for the Pb₃V(PO₄)₃ compound.     

Synthesis and characterization of CDs/Al2O3 nanofibers nanocomposite for Pb2+ ions adsorption and reuse for latent fingerprint detection

This study reports a new approach of preparation of carbon dots coated on aluminum oxide nanofibers (CDs/Al₂O₃NFs) nanocomposite and reusing the spent adsorbent of lead (Pb²⁺) ions loaded adsorbent (Pb²⁺-CDs/Al₂O₃NFs) nanocomposite for latent fingerprint detection (LFP) after removing Pb²⁺ ions from aqueous solution. CDs/Al₂O₃NFs nanocomposite was prepared by using CDs and Al₂O₃NFs with adsorption processes. The prepared nanocomposite was then characterized by using UV–visible spectroscopy (UV–visible), Fourier transforms infrared spectroscopy (FTIR), Fluorescence, X-ray diffraction pattern (XRD), scanning electron microscope (SEM), Transmission electron microscopy (TEM), Energy-dispersive X-ray spectroscopy (EDS), Zeta potential, X-ray photoelectron spectroscopy (XPS). The average size of the CDs was 51.18 nm. The synthesized CDs/Al₂O₃NFs nanocomposite has proven to be a good adsorbent for Pb²⁺ ions removal from water with optimum pH 6, dosage 0. 2 g/L. The results were best described by the Freundlich Isotherm model. The adsorption capacity of CDs/Al₂O₃NFs nanocomposite showed the best removal of Pb²⁺ ions with q_m = (177. 83 mg/g), when compared to the previous reports. This adsorption followed the pseudo-second order kinetic model. ΔG and ΔH values indicated spontaneity and the endothermic nature of the adsorption process. CDs/Al₂O₃NFs nanocomposite therefore showed potential as an effective adsorbent. The data were observed from adsorption–desorption after 6 cycles which showed good adsorption stability and re- usability of CDs/Al₂O₃NFs nanocomposite. Furthermore, the spent adsorbent of Pb²⁺-CDs/Al₂O₃NFs nanocomposite has proven to be sensitive and selective for LFP detection on various porous substrates. Hence Pb²⁺-CDs/Al₂O₃NFs nanocomposite can be reused as a good fingerprint labelling agent in LFP detection so as to avoid secondary environmental pollution by disposal of the spent adsorbent.     

Sonochemical synthesis and characterization of a nanostructured 3-D lead(II) coordination polymer with 4-methoxybenzoyltrifluoroacetone

Nanoparticles of a 3-D coordination polymer, [Pb₂(mbtfa)₄] _n (1) (Hmbtfa?=?4-methoxybenzoyltrifluoroacetone), have been synthesized by a sonochemical method. The nanomaterial was characterized by scanning electron microscopy, X-ray powder diffraction, IR spectroscopy, and elemental analyses. Compound 1 was structurally characterized by single-crystal X-ray diffraction. The structure of 1 shows the compound is triclinic and consists of 3-D polymeric units.     

Vibrational spectroscopic study of mimetite-pyromorphite solid solutions

A number of compounds of the mimetite Pb₅(AsO₄)₃Cl-pyromorphite Pb₅(PO₄)₃Cl solid solution series were synthesized at room temperature and analyzed with Raman and infrared spectroscopy. The fundamental antisymmetric stretching (ν₃) and bending (ν₄) vibrations of the mimetite-pyromorphite solid solutions occur in the regions 720-1040 cm⁻¹ and 400-580 cm⁻¹. The band originating from the ν₃ and ν₄ modes shifts to higher wavenumbers between mimetite and pyromorphite because the atomic mass of As is higher than P and As-O bonds are longer than P-O bonds. The position, shape and relative intensity of the bands vary primarily as a function of As/(As + P) in the analyzed solid. The strong correlations between the positions of the vibrational modes and the As/(As + P) ratio can be used to determine the composition of the investigated natural and synthetic samples of the minerals from the mimetite-pyromorphite series.     

唐代彩绘陶俑中无机颜料的化学组成

采用X射线粉末衍射（XRD）、X射线荧光光谱（XRF）和扫描电子显微镜-能谱（SEM-EDS）等测试技术对西安西曹M16唐墓出土的2尊唐代彩绘陶俑颜料进行了化学组成分析。结果表明,陶俑中含有丰富的无机颜料,其中红色颜料的显色成分为铅丹（Pb₃O₄）;白色颜料的显色成分为铅白（PbCO₃）和石灰石（CaCO₃）;粉色颜料的主要显色成分为铅丹和铅白的混合物;青色颜料为铜绿（Cu₂（OH）₂CO₃）和青石（Cu₃（OH）₂（CO₃）₂）混合物。