Redox Potentials of High-Valent Iron-, Cobalt-, and Nickel-Oxido Complexes: Evidence for Exchange Enhanced Reactivity

The ferrocene titration method has been employed to determine the one-electron reduction potentials of a series of oxido-iron(IV), oxido-cobalt(IV) and oxido/hydroxido-nickel(III) complexes based on the same tetradentate TMG₃tren ligand (TMG₃tren=tris[2-(N-tetramethylguanidyl)ethyl]amine). The S=2 ground state of the [(TMG₃tren)Fe^IV=O]²⁺ complex allows an exchange enhanced reactivity, which enables it to perform efficient oxygen atom transfer (OAT) and hydrogen atom abstraction (HAA) reactions with a low one-electron reduction potential of 270 mV vs. SCE. In the absence of exchange enhanced reactivity, the OAT and HAA abilities of the S=3/2 [(TMG₃tren)Co^IV−O(Sc(OTf)₃)]²⁺, S=1/2 [(TMG₃tren)Ni^III−O(H)]²⁺ and the previously reported S=1 [(TMC)(CH₃CN)Fe^IV=O]²⁺ and [(N4Py)Fe^IV=O]²⁺ complexes can be directly correlated to their reduction potentials. Notably, [(N4Py)Fe^IV=O]²⁺ and [(TMG₃tren)Fe^IV=O]²⁺ exhibit similar OAT and HAA reactivities although the reduction potential of [(N4Py)Fe^IV=O]²⁺ is 0.24 V more positive than that of [(TMG₃tren)Fe^IV=O]²⁺. The present study therefore provides experimental evidence for exchange enhanced reactivity and rationalizes nature's choice for employing S=2 oxido-iron(IV) cores to achieve difficult oxidation reactions at biologically viable potentials.     

New red pigments based on Li3AlMnO5 for NIR reflective cool coatings

The exploration of new red pigments based on transition elements is of great practical value in the field of inorganic pigments, since the red coloured pigments have unique applications in paints, ceramic tiles, cosmetics, etc. Here we mainly reported a new class of eco-friendly red pigments based on substituted Li₃AlMnO₅ (LAMO) and briefly state about the other rock salt layered structure Li₃GaMnO₅ (LGMO). The solid-state synthesized powders were crystallized to monoclinic structure having Mn^IV(1)_2b and Mn^IV(2)_4g site. The absorption bands in the synthesized samples mainly arises due to the octahedrally coordinated Mn^IVO₆ in the 4g site. Among the synthesized samples, LAMO: 0.10Ti⁴⁺ showed exemplary chromatic properties. The doping of tetravalent Ti⁴⁺ ions in the Mn⁴⁺ sites altered the Mn^IV(2)O₆ bond lengths and increased the crystal field around the absorption band attributed to the ⁴A_2g→⁴T_2g transitions. The ball milled LAMO: 0.10Ti⁴⁺shows the a* value of 40.05, which is higher than that of the commercially available red iron oxide pigments (a* = 28.9). Meanwhile, the brighter red powder LAMO: 0.10Ti⁴⁺ demonstrated appreciable thermal and chemical stability. From the thermal evaluating study, we observed that, LAMO: 0.10Ti⁴⁺ pigment coated roof panels showed a temperature difference of (3.2 °C) compared to the bare roof panel (3.7 °C). We estimated the coating's performance of the LAMO: 0.10Ti⁴⁺ in concrete block, metal plate and ceramic tile. In these substrates, the pigment possesses distinctly elevated NIR‐reflectance, which makes these materials worthwhile for cool coating applications.     

Determination of the Oxidation State of Antimony, Iron and Vanadium in Mixed Vanadium and Iron Antimonate Oxide Catalysts

Vanadium and mixed vanadium and iron antimonates with rutile-type structures have been studied by XANES at Sb L₁ edge, ⁵⁷Fe Mössbauer spectroscopy and ESR spectroscopy at 77 K. The results showed that both antimony and iron remained at their highest oxidation state, i.e. Sb^V and Fe^III, whereas vanadium was present as V^III and V^IV. Two types of V^IV species were distinguished corresponding to well-isolated vanadyl species in distorted octahedral coordination and vanadyl species in the same coordination but close to each other and in a dipole–dipole interaction. Both V^III and total V^IV concentrations decreased when the iron content increased, whereas isolated V^IV concentration increased first and then decreased, with a maximum for x = 0.2 in Fe_xV_1-xSbO₄. The observed variations in cationic composition are discussed in relation with the catalytic properties of the compounds in the ammoxidation of propane. Isolated V^IV-O moieties appeared to be the most active and selective catalytic sites.     

Synthesis,optical, and magnetic properties of six-layered Aurivillius bismuth ferrititanate

This work reports on the preparation, structure, photochemical, and magnetic properties of six-layered Aurivillius bismuth ferrititanates, that is, Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles. The samples were prepared through the modified citrate complexation and precursor film process. The XRD Rietveld refinements were conducted to study the phase formations and crystal structure. The morphological and chemical component characteristics were investigated using SEM, TEM, and EDX analyses. Bi₇Ti₃Fe₃O₂₁, Bi₇(Ti₂Nb)Fe₃O_21+δ, and Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticles present an indirect allowed transitions with band energies of 2.04, 2.03, and 2.02 eV, respectively. The hybridized (O2p+Fet_2g+Bi6s) formed the valence band (VB) and electronic components of (Ti–3d+Fe–e_g) formed the conduction band (CB) of this six-layered Aurivillius bismuth ferrititanate. The three samples showed efficient photocatalytic degradation of Rhodamine B (RhB) dyes with the excitation wavelength λ > 420 nm. The optical absorption, photodegradation, and magnetic abilities were improved through microstructural modification on “B” site via partial substitution of Mg²⁺ and Nb⁵⁺ for Ti⁴⁺. The photocatalytic results were discussed based on the layer structure and multivalent Fe ions. Fe^3+/2+ in the perovskite slabs (Bi₅Fe₃Ti₃O₁₉)²⁻ could act as the catalytic mediators in the photocatalysis process. As a photocatalyst, Aurivillius Bi₇(Ti₂Mg)Fe₃O_21−δ nanoparticle is advantageous due to its photocatalytic and magnetically recoverable abilities.     

Fabrication of Y and Fe co-doped BaZr0.13Ti1.46O3 fine-grained ceramics for temperature-stable multilayer ceramic capacitors

Y³⁺ and Fe³⁺ co-doped BaZr_0.13Ti_1.46O₃ powders were synthesized by wet chemical method through a precipitation process, able to control uniformity and particle size of the BaZr_0.13Ti_1.46O₃-based particles. Fine-grained BaZr_0.13Ti_1.46O₃ ceramics co-doped with various amounts of Y³⁺ and Fe³⁺ were prepared at low sintering temperature to yield good dielectric properties and gentle temperature stability. The co-doping effect on the microstructure and dielectric properties of BaZr_0.13Ti_1.46O₃ ceramics were studied. Results showed the dielectric constants firstly to increase monotonically then decrease with the increase of Y³⁺ and Fe³⁺concentration. Overall, the resulting ceramics met the X8R specification when Y³⁺ and Fe³⁺ contents were 2 or 4 mol%. Moreover, the increase in Y³⁺ and Fe³⁺ doping concentration from 6 to 8 mol% satisfied the X7R specification.     

New orthorhombic sodium iron(+2) titanate

The set of compositions with Fe²⁺ in the system Na_xFe_x/2Ti_2–x/2O₄ has been prepared by solid-state reactions in the inert atmosphere at 1050 °С. The oxidation state of iron was confirmed using the XANES method. Na_0.88Fe_0.44Ti_1.56O₄ is the new four-element compound in Na₂O–“FeO”–TiO₂ system. According to the X-ray powder data, it is orthorhombic, Pnma, a = 9.3624(1), b = 2.96718(4), c = 11.3435(1) Å and has the same structure as Na_0.9Fe_0.9Ti_1.1O₄ with Fe³⁺. The structure was refined by the Rietveld method. The 3D-framework of (Fe, Ti)O₆ octahedra contains quadruple rutile-like chains and sodium ions in double tunnels. Fe/Ti partial ordering in the framework and sodium distribution in the tunnels were studied additionally using the method of bond valence sums and Voronoi tessellation. The structure and composition of Na_0.88Fe_0.44Ti_1.56O₄ make it a promising material for cathode application.     

Understanding the voltage profile of Li insertion into LiNi0.5−yFeyMn1.5O4 in Li cells

LiNi_0.5−yM_yMn_1.5O₄ compounds have proven to be of great interest as active cathode material for high-voltage lithium-ion cells. The electrochemical behavior of LiNi_0.5−yFe_yMn_1.5O₄ compounds as cathode material in lithium cells is studied here. The charge-discharge curves are characterized by three main plateaus, ascribable to the removal (during charge) or filling (during discharge) of d electrons corresponding to the different redox pairs present: Fe^IV/Fe^III, Ni^IV/Ni^II and Mn^IV/Mn^III. Taking into account the entropy associated to the lithium extraction/insertion and the filling of the different electronic levels, the modelization gives a good reproducibility of the experimental electrochemical curves. The standard potential μ⁰ of the redox pairs were estimated to be ca. −4.90, −4.80 and −4.23 eV, respectively.     

Crystal symmetry and magnetism in Ti substituted Bi0.8Ba0.2FeO3 ceramic

The effect of Ti⁴⁺ substitution on the crystal structure and magnetic properties of the Bi_0.8Ba_0.2FeO₃ ceramic nanoparticles was investigated. Bi_0.8Ba_0.2Fe_1−xTi_xO₃ (x=0, 0.05, 0.10, 0.15 and 0.20) ceramics have been prepared by tartaric acid modified sol-gel method. Rietveld refinement of the XRD profile pattern of Bi_0.8Ba_0.2FeO₃ ceramic revealed the formation of pseudo-cubic (Pm3m) phase and confirms structural distortion on incorporation of Ti⁴⁺ ions, which consequently transform pseudo-cubic (Pm3m) structure to tetragonal (P4mm) structure. The saturation magnetization increases appreciably on Ti⁴⁺ ions substitution in Bi_0.8Ba_0.2FeO₃ and is found to be 0.57 emu/g for Bi_0.8Ba_0.2Fe_0.95Ti_0.05O₃ ceramic. The increase in the magnetization by the substitution of non-magnetic Ti⁴⁺ ions has been ascribed to crystal structure modification made by the Ti⁴⁺ ions. However, a sudden decrease in the magnetization has been observed for Bi_0.8Ba_0.2Fe_0.8Ti_0.2O₃ ceramic nanoparticles. The prominent Ti (3d) – O (2p) hybridization would stabilize the ferroelectric distortion and consequently reduce the magnetization. Scanning Electron Microscope (SEM) image of Bi_0.8Ba_0.2Fe_0.8Ti_0.2O₃ ceramic sample revealed the formation of dense microstructure with uniform grains size.     

Microstructural and multiferroic properties in layered perovskite-related Sm6Ti4Fe2O20

Layered perovskite-related Sm₆Ti₄Fe₂O₂₀ compound was successfully synthesized through the intercalation of bilayer SmFeO₃ into the Sm₂Ti₂O₇ with pyrochlore structure by means of floating-zone melting technique. The microstructural properties were characterized using aberration-corrected scanning transmission electron microscopy and X-ray diffraction. Electron energy-loss spectroscopy investigation reveals that the Fe³⁺ ions prefer to occupy the inner sites within the perovskite-like layers. This compound exhibits clearly the spin glass-like behavior as demonstrated by the magnetic properties measurement. Such complex magnetic behavior could be attributed to the partial chemical order of Ti/Fe over the B sites and the interactions between magnetic ions including Sm³⁺ and Fe³⁺. In addition, the multiferroic behavior with the coexistence of the ferroelectricity and ferromagnetism was well established by magnetic and piezoresponse measurements.     

The interaction of water-soluble iron porphyrins with DNA films and the electrocatalytic properties for inorganic and organic nitro compounds

The electrochemistry of water-soluble iron porphyrins (Fe(n-TMPyP)) (where n=2 and 4) was studied as an electrochemically active film on DNA modified glassy carbon, gold, platinum, and transparent semiconductor tin oxide electrodes in solutions of various pH values. The two layers of the modified electrode containing the iron porphyrin and the DNA film were prepared by depositing the iron porphyrin on a DNA film modified electrode. The Fe(4-TMPyP)/DNA film was electrocatalytic reductive for p-nitrobenzoic acid in a weak acidic, or neutral aqueous solution through an Fe^II species, and the electrocatalytic reduction peak potential became more negative than the cathodic peak of the Fe^III/II redox couple. The electrocatalytic reduction properties by the Fe(2-TMPyP)/DNA film as catalysts for nitrite reduction have also been determined, and shown to be active through an Fe^I species and to be pH-dependent. The electrocatalytic oxidation properties of nitrite by Fe(n-TMPyP)/DNA (for n=2 and 4) film have also been determined and shown to be active through an Fe^IV species with the electrocatalytic oxidation efficiency of NO₂⁻ with Fe^IV(O)(n-TMPyP) being higher than with (HO)Fe^IV(O)(n-TMPyP). The electrocatalytic oxidation efficiency of NO₂⁻ by iron porphyrin is pH-dependent. The electrocatalytic reduction of p-nitrophenol by Fe(2-TMPyP)/DNA film are also discussed.     

A Dinucleating Ligand System with Varying Terminal Donors to Mimic Diiron Active Sites

To mimic dinuclear active sites of metalloproteins, we have developed a dinucleating ligand system consisting of two tetradentate tripodal ligand compartments with varying terminal donors (carboxylates, phenolates, and pyridines). These ligands provide access to a series of μ-oxo-bridged diferric complexes. The spectroscopic study allows to investigate the molecular structures even in solution, e. g. depending on protonation/deprotonation of coordinated OH⁻ and H₂O ligands or to observe a reversible pH-dependent carboxylate-shift between terminal and bridging binding mode. The electrochemical behavior is strongly influenced by the exogenous ligands, e. g. OH⁻ facilitates oxidation to Fe^IV by 690 mV relative to Cl⁻. Using the terminal carboxylates and a {Fe^III(μ-O)₂Fe^III} core even allows oxidation with O₂ to a high-valent species with Fe^IV (S=2). The implications of this study for further generation of high-valent or peroxo species and their utilization in catalysis is discussed.     

Oxygen hyper stoichiometric trimetallic titanium doped magnesium ferrite: Structural and photocatalytic studies

Oxygen hyper stoichiometric titanium doped magnesium ferrite, Mg_1-xTi_xFe₂O_4+δ (x = 0–1.0) nanoparticles (NPs) were synthesized using sol-gel method. XRD analysis revealed a decrease in the lattice parameter from 8.9 to 8.3 Å and confirmed the incorporation of Ti⁴⁺, a smaller ionic radius dopant. Presence of M-O vibrational bands at tetrahedral and octahedral sites were authenticated by FT-IR analysis. The observed reduction in saturation magnetization values from 23.3 emug^?1 to 18.3 emug^?1 was ascribed to the doping of non-magnetic Ti⁴⁺ ions in MgFe₂O₄ NPs. BET studies corroborated the mesoporous nature of the NPs and doped ferrite NPs displayed larger surface area (53.0–73.0 m²g^-1) as compared to pristine ferrite NPs (32.8–39.0 m²g^-1). Optical studies displayed red shift in the absorption edge of the Ti⁴⁺ doped MgFe₂O₄ NPs in contrast to pristine NPs. Oxygen hyper stoichiometry in the doped ferrite NPs was determined experimentally. Photoluminescence emission spectra exhibited reduction in the emission intensity in case of Ti⁴⁺ doped NPs which supported their higher light capturing potential. Among synthesized doped ferrite NPs Mg_0.5Ti_0.5Fe₂O_4.5 NPs exhibited maximum (98%) photodegradation capacity for rhodamine B. The ^?O₂^? and ^?OH were the main reactive species in the photodegradation. The present studies have clearly shown the potential of tuning the composition of oxygen hyper stoichiometric ferrite Mg_0.5Ti_0.5Fe₂O_4.5 for the removal of toxic organic contaminants from water.     

Theoretical studies on high-valent manganese porphyrins: Toward a deeper understanding of the energetics,electron distributions,and structural features of the reactive intermediates of enzymatic and synthetic manganese-catalyzed oxidative processes

We present here a relatively comprehensive theoretical study, based on nonlocal density functional theory calculations, of the energetics, electron distributions, and structural features of the low-lying electronic states of various high-valent intermediates of manganese porphyrins. Two classes of molecules have been examined: (a) compounds with the general formula [(P)MnX₂]⁰ (P = porphyrin; X = F, Cl, PF₆) and (b) high-valent manganese-oxo species. For [(P)Mn(PF₆)₂]⁰, the calculations reveal a number of nearly equienergetic quartet and sextet states as the lowest states, consistent with experimental results on a comparable species, [(TMP)Mn(ClO₄)₂]⁰ (TMP = tetramesitylporphyrin). In contrast, [(P)MnCl₂]⁰ and [(P)MnF₂]⁰ have a single well-defined S = 3/2 Mn(IV) ground state, again in agreement with experiment, with the three unpaired spins largely concentrated (>90%) on the manganese atom. Manganese(IV)-oxo porphyrins have an S = 3/2 ground state, with the three unpaired spins distributed approximately 2.3:0.7 between the manganese and oxygen atoms. The metal-to-oxygen spin delocalization, as measured by the oxygen spin population, for Mn^IV = O porphyrins is less than, but still qualitatively similar to, that in analogous iron(IV)-oxo intermediates, indicating that the Mn^IV = O bond is significantly weaker than the Fe^IV = O bond in an analogous molecule. Thus, the optimized metal—oxygen bond distances are 1.654 and 1.674 Å for (P)Fe^IV(O)(Py) and (P)Mn^IV(O)(Py), respectively (Py = pyridine). This is consistent with the experimental observation that Mn^IV = O stretching frequencies are over 10% lower than Fe^IV = O stretching frequencies for analogous compounds. For [(P)Mn(O)(PF₆)]⁰, [(P)Mn(O)(Py)]⁺, and [(P)Mn(O)(F)]⁰, the ground states clearly correspond to a (d_xy)² Mn(V) configuration and the short Mn–O distances of 1.541, 1.546, and 1.561 Å for the three compounds, respectively, reflect the formal triple bond character of the Mn–O interaction. Interestingly, the corresponding Mn(IV)-oxo porphyrin cation radical states are calculated to be a few tenths of an electrovolt higher than the Mn(V) ground states, suggesting that the Mn(IV)-oxo porphyrin cation radicals are not likely to exist as ground-state species.     

Structural and multiferroic properties of Pr and Ti co-doped BiFeO3 ceramics

Bi_0.9Pr_0.1FeO₃ (BPF), BiFe_0.9Ti_0.1O₃ (BFT), Bi_0.9Pr_0.1Fe_0.9Ti_0.1O₃ (BPFT-10), and Bi_0.9Pr_0.1Fe_0.95Ti_0.05O₃ (BPFT-5) ceramics are prepared for a comparison study. X-ray diffraction indicates that all of the samples crystallize in rhombohedral structures with R3c symmetry. The Pr and Ti co-doped samples show an especially low dielectric loss of 0.02–0.04 throughout the entire investigated frequency range. A markedly improved polarization hysteresis loop is successfully achieved for samples BPFT-10 and BPFT-5, and their remnant polarization P_r values are 0.11 and 0.29 μC/cm², respectively. Magnetic measurements indicate that the substitution of Ti⁴⁺ for Fe³⁺ improves the ferromagnetic properties due to the suppression of the spiral spin structure. A remnant magnetization M_r of 0.176 emu/g was observed for BPFT-10 at 5 K.     

Formation of anisotropic grains and modified ferroelectric properties in Cr-doped Bi5FeTi3O15 thin films

Aurivillius phase Bi₅Cr_xFe_1−xTi₃O₁₅ (0≤ x ≤1) thin films are prepared by the chemical solution deposition method, and the effect of Cr content on the microstructure, ferroelectric property, and electric transport behavior of Bi₅Cr_xFe_1−xTi₃O₁₅ films is investigated. X-ray diffraction analysis shows that all of Bi₅Cr_xFe_1−xTi₃O₁₅ films are complete solid solution and maintain the Aurivillius structure. The replacement of Fe³⁺ with smaller Cr³⁺ decreases anisotropy and lattice aspect ratio in a-b plane, which is minimized at the composition of Bi₅Cr_0.5Fe_0.5Ti₃O₁₅. This changes the grain shape from sphere to plate, and Bi₅Cr_0.5Fe_0.5Ti₃O₁₅ film consists of only plate-like grains. Cr doping increases saturated polarization (P_m) and decreases coercive field (E_c). Cr doping increases P_m of Bi₅Cr_xFe_1−xTi₃O₁₅ film to 35 μC/cm², but decreases E_c down to 125 kV/cm. A decrease in the lattice aspect ratio of a-b plane promotes the alignment of ferroelectric dipoles under electric field. The frequency-dependent dielectric property and the leakage current show that the plate-like grains of Cr-rich Bi₅Cr_xFe_1−xTi₃O₁₅ films suppress the transport of carriers from grains to grains and prevents a dramatic leakage current increase. The results of this study provide a design rule to control the ferroelectricity of Aurivillius phase Bi₅Cr_xFe_1−xTi₃O₁₅ thin films by modifying the composition and lattice aspect ratio.     

Decolorization of methylene blue by heterogeneous Fenton reaction using Fe3−xTixO4 (0 ≤ x ≤ 0.78) at neutral pH values

In this work, a series of Fe_3−xTi_xO₄ (0 ≤ x ≤ 0.78) was synthesized using a new soft chemical method. The synthetic Fe_3−xTi_xO₄ were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Mössbauer spectroscopy, thermogravimetric and differential scanning calorimetry (TG–DSC) analyses. The results showed that they were spinel structures and Ti was introduced into their structures.Then, decolorization of methylene blue (MB) by Fe_3−xTi_xO₄ in the presence of H₂O₂ at neutral pH values was studied using UV–vis spectra, dissolved organic carbon (DOC) and element C analyses. Furthermore, the degradation products remained in reaction solution after the decolorization were identified using ionic chromatography (IC), ¹³C nuclear magnetic resonance spectra (NMR), liquid chromatography and mass spectrometry (LC–MS). Although small amounts of MB were mineralized, the aromatic rings in MB were destroyed completely after the decolorization. Decolorization of MB by Fe_3−xTi_xO₄ in the presence of H₂O₂ was promoted remarkably with the increase of Ti content in Fe_3−xTi_xO₄ due to the enhancement of both adsorption and degradation of MB on Fe_3−xTi_xO₄.     

Andradite titanium: Preparation,characterization and metallurgical performance

Andradite titanium (Ca₃Fe₂Si_1.58Ti_1.42O₁₂, abbreviated as AT), which is a significant mineral phase in the sinter of titanium-containing iron ore, was prepared via a solid-state reaction with analytical reagents. The crystal structure, cold strength, and high-temperature heat capacity were individually characterized, and the metallurgical performance, such as melting and reduction behavior, were measured. AT is a variant of andradite (Ca₃Fe₂Si₃O₁₂) formed by the Ti⁴⁺ substitution for Fe³⁺ in the octahedral sites and Fe³⁺ substitution for Si⁴⁺ in the tetrahedral sites. The compressive strength of AT was approximately 14.21 MPa, and its softening, melting, and flowing temperatures were 1453, 1483, and 1509 K, respectively. According to the differential scanning calorimetry measurements, the melting point was approximately 1502 K. The non-isothermal reduction results revealed that AT was reduced to Fe, perovskite, and wollastonite in a single step, and the isothermal reduction test indicated that the reduction degree of AT was only 0.67 when reduced at 900°C for 150 min, and the order of reduction performance was Fe₂O₃ > Fe₃O₄ > CaO·2Fe₂O₃ > CaO·Fe₂O₃ > 2CaO·Fe₂O₃ > AT. The high-temperature heat capacity of AT as a function of temperature was also measured and modeled.     

Structural transformation and multiferroic properties of Sm and Ti co-doped BiFeO3 ceramics with Fe vacancies

Sm and Ti co-doped BiFeO₃ (BFO) ceramics with Fe vacancies—Bi_0.86Sm_0.14FeO₃, Bi_0.86Sm_0.14Fe_0.99Ti_0.01O₃, and Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃—were prepared by a solid-state method using a rapid liquid process. X-ray diffraction indicated that all samples exhibited a rhombohedral structure with a minor secondary phase. The structural transformation from a rhombohedral (space group: R3c) to orthorhombic structure (space group: Pnma) was observed in the sample of Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃, which was also confirmed by Raman scattering spectra. Microstructural investigations with scanning electron microscopy showed a reduction in grain size with doping of BFO. The dielectric loss of Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃ reaches 0.05 (at 100 Hz) owing to the introduction of Ti and Fe vacancies. Ferroelectromagnetic measurements revealed the existence of ferroelectricity with a remanent polarization of 0.24 µC/cm² in Bi_0.86Sm_0.14FeO₃, paraelectricity in Bi_0.86Sm_0.14Fe_0.9Ti_0.05O₃, and weak ferromagnetism with a remanent magnetization of 0.2 emu/g in Bi_0.86Sm_0.14Fe_0.99Ti_0.01O₃. The two composition-driven phases exist simultaneously and the different coercive field might be related to the jumps in the ferromagnetic hysteresis loops. Both the ferroelectric and magnetic properties were shown to correlate with the composition-driven structural evolution.     

Incompatible magnetic and dielectric properties of BiCu3-xMnxTi4-yMyO12 (x = 0 & 0.5; y = 1 & 1.5 and M = Fe & Mn)

Here we report ambient pressure synthesis, magnetic and dielectric properties of BiCu₃Ti₃(Fe/Mn)O₁₂ and BiCu_2.5Mn_0.5Ti_2.5Fe_1.5O₁₂. Both the samples are crystallized in a cubic Im-3 space group. The antiferromagnetic ground state of A-site copper in Bi_2/3Cu₃Ti₄O₁₂ is differently affected by substitution of nonmagnetic Ti⁴⁺ by magnetic Fe and Mn ions in B-site. In contrast to the Mn substitution, the antiferromagnetic ordering of A-site Cu is robust towards Fe substitution. The substitution of iron for Ti⁴⁺ initially weakens the antiferromagnetic structure of A-site Cu and eventually it results in the crossover from antiferromagnetic to ferrimagnetic state, whereas the Mn substitution quickly turns antiferromagnetic to ferrimagnetic state. For x > 1.0 Fe-doped sample and low Mn-doped samples exhibit phase separation where the ferromagnetic like phase coexists with antiferromagnetic phase. The glassy magnetic state is realized for x = 1.0 Fe doped sample. The magnetic ground state strongly influences the dielectric behavior of the samples. Near room temperature the dielectric constant value is ~2000 for BiCu₃Ti₃FeO₁₂, whereas for BiCu_2.5Mn_0.5Ti_2.5Fe_1.5O₁₂ the value is much lower (<600) with higher dielectric loss. The leaky nature in magnetically phase separated BiCu_2.5Mn_0.5Ti_2.5Fe_1.5O₁₂ can be ascribed to the opening of conducting ferrimagnetic channels. The present investigation revealed that in quadruple perovskite the magnetic and dielectric properties are incompatible where improvement of magnetic response eventually suppresses the dielectric behavior.     

Dissolution of pastes in lead-acid battery recycling plants

The dissolution of the active materials of lead-acid batteries in fluoboric electrolyte has been studied. The use of redox couples such as Ti³⁺/Ti⁴⁺ is proposed for an efficient and quick dissolution of lead and lead dioxide mixtures. For PbO₂ and Pb electrodeposited on platinum electrodes the rate of dissolution in HBF₄ (200 g dm⁻³) containing Ti ions (0.3m) corresponds to a current density of 400 A cm⁻² and 160 A cm⁻², respectively. Dissolved oxygen has a marked influence on lead dissolution acting as an oxidizer of Ti³⁺ to Ti⁴⁺. It has also been shown that the Fe²⁺/Fe³⁺ couple can be used, although with lower benefits. For industrial applications, a concentration of Ti ions of about 0.051m and the use of a counter-current electrolyte flow in the electrolysis cell can advantageously accomplish the leaching process of pastes and slimes in a batteries recycling plant.