Mechanisms for the formation of layered A<Subscript>4</Subscript>B<Subscript>3</Subscript>O<Subscript>12</Subscript> compounds from coprecipitated hydroxocarbonate and hydroxide systems

We have established and analyzed the sequences of phase transitions in synthesis of layered compounds in the A_nB_n–1O_3n family ( \textA₃^\textII\textLnB₃^\textV\textO₁₂ {\text{A}}_3^{\text{II}}{\text{LnB}}_3^{\text{V}}{{\text{O}}_{{12}}} (A^II = Ba, Sr, Ln = La, Nd, B^V = Nb, Ta) and La₄Ti₃O₁₂ with n = 4) from coprecipitated hydroxocarbonate and hydroxide systems, including steps involving the formation, solid-phase reaction, or structural rearrangement of intermediates.     

Solid Solutions of the System V<Subscript>2</Subscript>O<Subscript>5</Subscript>-V<Subscript>2</Subscript>O<Subscript>4</Subscript>-TiO<Subscript>2</Subscript> in Air

Gravimetry in combination with X-ray phase analysis, X-ray crystallography, and X-ray densitometry were used to determine the contents of V⁵⁺, V⁴⁺, and Ti⁴⁺ ions and vacancies in solid solutions formed by the reaction of V₂O₅ with TiO₂ in air at atmospheric pressure.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

New phase in the system FeVO<Subscript>4</Subscript>-Cd<Subscript>4</Subscript>V<Subscript>2</Subscript>O<Subscript>9</Subscript>

A new phase Cd₄Fe_7+xV_9+xO_37+4x, where −0.5<x<1.5, has been obtained in the solid-state in the FeVO₄−Cd₄V₂O₉ system. The temperature of incongruent melting and the unit cell volume of this phase decrease with decreasing the content of cadmium. The IR spectrum and SEM image of the new phase are presented.     

Notable enlargement of remnant polarization for fatigue-free SrBi4Ti4O15 thin films by La-substitution

La-doped SrBi₄Ti₄O₁₅, SrBi_4–x La _x Ti₄O₁₅ (SBLT-x, x = 0.00, 0.10 and 0.25), thin films have been successfully prepared by the sol–gel method. Structures, surface morphology and ferroelectric properties were investigated. Compared with undoped SBTi, SBLT-0.10 shows a notable larger remnant polarization (2P _r = 46 μC/cm²). Meanwhile, the SBLT-0.10 film shows little change of P _nv and −P _nv up to 4.4 × 10¹⁰ switching cycles, suggesting an excellent fatigue-endurance characteristics.     

Microstructure and properties of sol-gel derived Pb(Zr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>)O<Subscript>3</Subscript> thin films on GaN/sapphire for nanoelectromechanical systems

Highly (111) oriented, phase-pure perovskite Pb(Zr_0.3Ti_0.7)O₃ (or PZT 30/70) thin films were deposited on single-crystal, (0001) wurtzite GaN/sapphire substrates using the sol-gel process and rapid thermal annealing. The phase, crystallinity, and stoichiometry of annealed PZT films were evaluated by X-ray diffraction and Rutherford backscattering spectroscopy. The atomic force microscopy revealed a smooth PZT surface (rms roughness ∼1.5 nm) with striations and undulations possibly influenced by the nature of the underlying GaN surface. The cross-sectional field-emission scanning electron microscopic images indicated a sharper PZT/GaN interface compared to that of sol-gel derived PZT on (111) Pt/TiO₂/SiO₂/(100) Si substrates. The capacitance-voltage (C-V) characteristics for PZT in the Pt/PZT/GaN (metal-ferroelectric-semiconductor or MFS) configuration were evaluated as a function of annealing temperature and applied voltage. The observed C-V hysteresis stemmed from trapped charge at defect sites within PZT. Also, the lower capacitance density (C/A = 0.35 μF/cm², where A is the area of an electrode) and remnant polarization (P _r ∼ 4 μC/cm²) for PZT in the MFS configuration, compared to the values for PZT in the MFM configuration (Pt/PZT/Pt), were attributed to the high depolarization field within PZT.     

A novel Et<Subscript>4</Subscript>NBF<Subscript>4</Subscript> and LiPF<Subscript>6</Subscript> blend salts electrolyte for supercapacitor battery

Electrolytes of 1 M blend salts (LiPF₆ and tetraethylammonium tetrafluoroborate, Et₄NBF₄) have been investigated in supercapacitor battery system with composite LiMn₂O₄ and activated carbon (AC) cathode, and Li₄Ti₅O₁₂ anode. The results obtained with the blend salts electrolytes are compared with those obtained with cells build using standard 1 M LiPF₆ dissolved in ethylene carbonate + dimethyl carbonate + ethyl (methyl) carbonate (EC + DMC + EMC, 1:1:1 wt.%) as electrolyte. It is found that the blend salts electrolyte performs better on both electrochemical and galvanostatic cycling stability, especially cycled at 4 C rate. When the concentration of LiPF₆ is 0.2 M and Et₄NBF₄ is 0.8 M, the capacity retention of the battery is 96.23% at 4 C rate after 5,000 cycles, much higher than that of the battery with standard 1 M LiPF₆ electrolyte, which is only 62.35%. These results demonstrate that the blend salts electrolyte can improve the galvanostatic cycling stability of the supercapacity battery. Electrolyte of 0.2 M LiPF₆ + 0.8 M Et₄NBF₄ in EC + DMC + EMC (1:1:1 wt.%) is a promising electrolyte for (LiMn₂O₄ + AC)/Li₄Ti₅O₁₂.     

Effect of heat treatment on particle growth and magnetic properties of electrospun Sr<Subscript>0.8</Subscript>La<Subscript>0.2</Subscript>Zn<Subscript>0.2</Subscript>Fe<Subscript>11.8</Subscript>O<Subscript>19</Subscript> nanofibers

Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉/poly(vinyl pyrrolidone) (PVP) composite fiber precursors were prepared by the sol–gel assisted electrospinning. Subsequently, the M-type ferrite Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers with diameters about 120 nm were obtained by calcination of these precursors at different heat treatment conditions. The precursor and resultant Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectrometer and vibrating sample magnetometer. With the calcination temperature increased up to 1,000 °C for 2 h or the holding time prolonged to 12 h at 900 °C, the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ particles gradually grow into a hexagonal elongated plate-like morphology due to the dimensional control along the nanofiber length. These elongated plate-like particles will be linked one by one to form the nanofiber with a necklace-like morphology. The magnetic properties of the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers are closely related to grain sizes, impurities and defects in the ferrite, which are influenced by the calcination temperature, holding time and heating rate. After calcined at 900 °C for 12 h with a heating rate of 3 °C/min, the optimized magnetic properties are achieved with the specific saturation magnetization 75.0 A m² kg⁻¹ and coercivity 426.3 kA m⁻¹ for the Sr_0.8La_0.2Zn_0.2Fe_11.8O₁₉ nanofibers.     

Kinetics of phase formation upon the treatment of La<Subscript>2</Subscript>(SO<Subscript>4</Subscript>)<Subscript>3</Subscript> and La<Subscript>2</Subscript>O<Subscript>2</Subscript>SO<Subscript>4</Subscript> in a hydrogen flow

The sequence of phases occurring during treatment of lanthanum sulfate, La₂(SO₄)₃ and lanthanum oxysulfate, La₂O₂SO₄ in a hydrogen flow is established. The temperature ranges in which homogeneous La₂O₂S is produced are revealed: when La₂(SO₄)₃ is a precursor, the range is 770–1220 K; in the case of La₂O₂SO₄, the interval is 950–1220 K. The kinetic curves showing the time dependence of the yield of La₂O₂S is constructed and treated using the Avrami-Erofeev and contracting volume equations. The activation energies of the reactions are determined.     

A New Molybdophosphate Constructed From {Mo<Stack><Subscript>2</Subscript><Superscript>V</Superscript></Stack>O<Subscript>4</Subscript>(H<Subscript>2</Subscript>O)<Subscript>6</Subscript>}<Superscript>2+</Superscript> and 1-Hydroxyethylidenediphosphonate

A new molybdophosphate (NH₄)₈{Mo₂^VO₄[(Mo₂^VIO₆)CH₃C(O)(PO₃)₂]₂}·14H₂O (1), has been synthesized by the reaction of {Mo₂^VO₄(H₂O)₆}²⁺ fragments with 1-hydroxyethylidenediphosphonate (hedp HOC(CH₃)(PO₃H₂)₂), and it is characterized by ³¹P NMR, IR, UV, element analysis, TG and single-crystal X-ray analysis. The structure analysis reveals that the polyoxoanion can be described as two {(Mo₂^VIO₆)(CH₃C(O)(PO₃)₂} units connected by a {Mo₂^VO₄}²⁺ moiety. In the structure, the six Mo atoms are arranged into a new “W-shaped” structure, which represents a new kind of molybdophosphate.     

Electrochemical properties of perovskite and A<Subscript>2</Subscript>MO<Subscript>4</Subscript>-type oxides used as cathodes in protonic ceramic half cells

Three selected materials have been prepared and shaped as cathode of half cells using the proton-conducting electrolyte BaCe_0.9Y_0.1O_3 − δ (BCY10): two perovskite compounds, Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3 − δ (BSCF) and La_0.6Sr_0.4Fe_0.8Co_0.2O_3 − δ (LSFC), and the praseodymium nickelate Pr₂NiO_4 + δ (PRN) having the K₂NiF₄-type structure. The electrochemical properties of these compounds have been studied under zero current conditions (two-electrode cell) and under polarization (three-electrode cell). Their measured area-specific resistances were about 1–2 Ω cm² at 600 °C. Under direct current polarization, it appears that the three compounds show almost similar values of current densities at 625 °C; however, at lower temperatures, BSCF appears to be the most efficient cathode material.     

Microstructure and electrical properties of lead zirconate titanate thin films deposited by sol-gel method on La<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>MnO<Subscript>3</Subscript>/SiO<Subscript>2</Subscript>/Si substrate

(La_0.7Sr_0.3)MnO₃ thin films were deposited on SiO₂/Si substrates by a metal-organic decomposition (MOD) method, and then Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films were grown on (La_0.7Sr_0.3)MnO₃-coated SiO₂/Si substrates by a sol-gel method. The effects of annealing temperature on the crystalline phases, microstructures and electrical properties of the PZT films were investigated. X-ray diffraction analysis results indicated that the PZT films with a perovskite single phase could be obtained by annealing at 650°C. The dielectric constant and the remnant polarization of the PZT films increased with increasing annealing temperature. The remnant polarization and the coercive field of the films annealed at 650°C were 18.3 μC/cm² and 35.5 kV/cm, respectively, whereas the dielectric constant and loss value measured at 1 kHz were approximately 1100 and 0.81, respectively.     

Preparation and electrical properties of Nd and Mn co-doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films

Ferroelectric thin films of Nd and Mn co-doped bismuth titanate, Bi_3.15Nd_0.85Ti_3−x Mn _x O₁₂ (BNTM) (x = 0–0.1), were fabricated on Pt/TiO₂/SiO₂/Si(100) substrates by a sol–gel technique. The BNTM films had a polycrystalline perovskite structure and uniform and dense surface morphologies. A lattice distortion was observed in the BNTM films due to Mn ion doping. The ferroelectric measurement of the films indicated that the values of coercive field (E _c ) decreased gradually with the increase of the Mn content (x), however, the remanent polarization (P _r ) increase firstly and then decrease with the increase of x. The sample with x = 0.05 had optimum electrical properties and a maximum 2P _r value. The 2P _r and 2E _c values of the film at a maximum applied electric field of 400 kV/cm were 38.3 μC/cm² and 180 kV/cm, respectively. Moreover, this BNTM capacitors did not show fatigue behaviors after 1.0 × 10¹⁰ switching cycles at a frequency of 1 MHz, suggesting a fatigue-free character. The main reason for the increase of the 2P _r and the decrease of the 2E _c might be attributed to the lattice distortion in BNTM films due to Mn ion doping.     

Hydrothermal Syntheses and Crystal Structures of Two New Heteropolyoxovanadoborates Containing {(VO)<Subscript>12</Subscript>O<Subscript>6</Subscript>[B<Subscript>3</Subscript>O<Subscript>6</Subscript>(OH)]<Subscript>6</Subscript>(H<Subscript>2</Subscript>O)} Cluster

Two new heteropolyoxovanadoborates (H₂dap)₂H₆{(VO)₁₂O₆[B₃O₆(OH)]₆(H₂O)}·13H₂O (1, dap = 1,2-diaminopropane) and {[Zn(dien)]₂[Zn(dien)(H₂O)]₄(VO)₁₂O₆[B₃O₆(OH)]₆(H₂O)}₂·15H₂O (2, dien = diethylenetriamine) have been hydrothermally synthesized and structurally characterized. Both 1 and 2 contain {(VO)₁₂O₆[B₃O₆(OH)]₆(H₂O)} cluster (denoted on V₁₂B₁₈), which is constructed by a puckered B₁₈O₃₆(OH)₆ ring sandwiched between two triangles of six alternating cis and trans edge-sharing vanadium atoms, and a central water molecule. 1 consists of discrete [V₁₂B₁₈]¹⁰⁻ cluster anions with H₂dap²⁺ as counterions, while 2 consists of discrete neutral {[Zn(dien)]₂[Zn(dien)(H₂O)]₄[V₁₂B₁₈]} clusters, which are built from two types of zinc(II) complex fragments connecting with V₁₂B₁₈ cluster through two Zn-(μ ₃-O)-B bonds. Interestingly, 2 is the only example of the V₁₂B₁₈ cluster decorated by two types of zinc(II) complex fragments.     

Phase formation in the FeVO<Subscript>4</Subscript>–Co<Subscript>3</Subscript>V<Subscript>2</Subscript>O<Subscript>8</Subscript> system

Phase relations in the solid state in the FeVO₄–Co₃V₂O₈ system, in the whole range of components concentration have been studied. It was found that the composition of the phase of the howardevansite type structure, formed in the investigated system, corresponds with the Co_2.616Fe_4.256V₆O₂₄ formula. The phase of the lyonsite type structure has a homogeneity range with the Co_3+1.5xFe_4–xV₆O₂₄ formula (0.476 formula (0.476<x<1.667). The melting temperature and the volume of the unit cell of the lyonsite type structure phase increases together with the rise of cobalt quantity contained in it. Basing on the results of the DTA and XRD measurements a phase diagram of the FeVO_4–Co₃V₂O₈ system up to the solidus line was constructed.     

Phase formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

Solid-phase interactions in the V₂O₅-Ta₂O₅-MoO₃ system were studied. The formation of com- pounds TaVO₅ and VTa₉O₂₅ in the V₂O₅-Ta₂O₅ binary system was verified. Tetragonal VTa₉O₂₅-base solid solutions of the general formula Ta_{5 + 4x} V_{5 − 4x} O₂₅ (x = 0.25–1) and TaVO₅-base solid solutions of the general formula Ta _x Mo_{1 − x} V_{2 − x} O_{8 − 3x} (x = 0.625–1) were found to form. Subsolidus phase equilibria in the V₂O₅-Ta₂O₅-MoO₃ were determined.     

Cellulose scaffolds modulated synthesis of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> nanocrystals: preparation,characterization and properties

Magnetic Co₃O₄ nanoparticles were prepared by using microporous regenerated cellulose films as sacrificial scaffolds. The cellulose macromolecules and the porous structure of the films made them used as spatially confined reacting sites where Co(OH)₂ nanoparticles could be synthesized in situ. When the cellulose matrix was removed by sintering at 500 °C, Co₃O₄ nanoparticles were obtained. XRD and XPS indicated that the prepared nanoparticles were pure Co₃O₄ without any impurity. TEM and SEM images revealed that the particle size of the nanoparticles was smaller than 100 nm. The nanoparticles had weak ferromagnetic properties at 25 °C. Furthermore, the pronounced quantum confinement effects of the synthesized nanoparticles have been observed, the optical bandgap energies determined were about 1.92 ~ 2.12 and 2.74 ~ 2.76 eV for O²⁻ → Co³⁺ and O²⁻ → Co²⁺ charge-transfer processes, respectively. Furthermore, the resulted Co₃O₄ nanoparticles behaved stable electrochemical performance with promising applications in the electrode for lithium ion battery.     

Synthesis and characterization of submicron size particles of LiMn<Subscript>2</Subscript>O<Subscript>4</Subscript> by microemulsion route

Among the various positive electrode materials investigated for Li-ion batteries, spinel LiMn₂O₄ is one of the most important materials. Small particles of the active materials facilitate high-rate capability due to large surface to mass ratio and small diffusion path length. The present work involves the synthesis of submicron size particles of LiMn₂O₄ in a quaternary microemulsion medium. The precursor obtained from the reaction is heated at different temperatures in the range from 400 to 900 °C. The samples heated at 800 and 900 °C are found to possess pure spinel phase with particle size <200 nm, as evidenced from XRD, SEM, and TEM studies. The electrochemical characterization studies provide discharge capacity values of about 100 mAh g⁻¹ at C/5 rate, and there is a moderate decrease in capacity by increasing the rate of charge–discharge cycling. Studies also include charge–discharge cycling and ac impedance studies in temperature range from −10 to 40 °C. Impedance data are analyzed with the help of an equivalent circuit and a nonlinear least squares fitting program. From temperature dependence of charge-transfer resistance, a value of 0.62 eV is obtained for the activation energy of Mn³⁺/Mn⁴⁺ redox process, which accompanies the intercalation/deintercalation of the Li⁺ ion in LiMn₂O₄.     

Preparation and electrochemical properties of V<Subscript>2</Subscript>O<Subscript>5</Subscript> submicron-belts synthesized by a sol–gel H<Subscript>2</Subscript>O<Subscript>2</Subscript> route

One-dimensional (1D) submicron-belts of V₂O₅ have been prepared by a sol–gel route using V₂O_5, H₂O₂ and aniline as starting materials. Thermogravimetric and differential thermal analysis, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy were employed to characterize the samples. Electrochemical behaviors as cathode material in rechargeable lithium-ion batteries were investigated by galvanostatic charge–discharge measurement and cyclic voltammeter. The results showed that the synthesized V₂O₅ appeared to be submicron-belts and orthorhombic structure. The V₂O₅ submicron-belts exhibited a high initial discharge capacity of 346 mAh/g and stayed 240 mAh/g after 20 cycles at 0.1 C discharge rate in the potential region 1.8–4.0 V.     

Ion state of atoms and the properties of perovskite-like compound CaCu<Subscript>3</Subscript>V<Subscript>4</Subscript>O<Subscript>12</Subscript>

The binding energies and valence state of atoms in the perovskite-like compound CaCu₃V₄O₁₂ have been determined using XPS spectroscopy. The stoichiometry of this phase is formulated as Ca²⁺Cu²⁺Cu ₂ ⁺ (V ₂ ⁵⁺ V ₂ ⁴⁺ O₁₂). Under an air atmosphere, the phase interacts with water vapor and oxygen. As a result, Ca(OH)₂ is formed on its surface, the Cu⁺ and V⁴⁺ ion concentrations decrease, and the Cu²⁺ and V⁵⁺ concentrations increase in association. Raman spectra show shortened cation-anion bond lengths and cation-anion-cation bond angles in CaCu₃V₄O₁₂ compared to perovskite CuVO₃; the two structures are alike. The electrical conductivity, magnetic susceptibility, thermal and sensor properties of CaCu₃V₄O₁₂ in aqueous salt solutions have been studied.