Sol–gel synthesis of nanocrystalline Zn1−xNixFe2O4 ceramics and its structural,magnetic and dielectric properties

Zn_1?xNi_xFe₂O₄ (0.0 ≤ x ≤ 1.0) nanoparticles are prepared by sol–gel method using urea as a neutralizing agent. The evaluation of XRD patterns and TEM images indicated fine particle nature. The average crystallite size increased from 10 to 24 nm, whereas lattice parameters and density decreased with increasing Ni content (x). Infrared spectra showed characteristic features of spinel structure along with a strong influence of compositional variation. Magnetic measurements reveal a maximum saturation magnetization for Zn_0.5Ni_0.5Fe₂O₄ (x = 0.5); however, reduced value of magnetization is attributed to the canted spin structure and weakening of Fe³⁺(A)–Fe³⁺(B) interactions at the surface of the nanoparticles. Impedance analysis for different electro-active regions are carried out at room temperature with Ni substitution. The existence of different relaxations associated with grain, grain boundaries and electrode effects are discussed with composition. It is suggested that x = 0.5 is an optimal composition in Zn_1?xNi_xFe₂O₄ system with moderate magnetization, colossal resistivity and high value of dielectric constant at low frequency for their possible usage in field sensor applications.     

The effect of introduction of manganese hydroxide and hydrated aluminum oxide on the pore structure and surface charge of Zr(IV), Ti(IV), and Sn(IV) oxyhydrates

The specific surface area, micropore volume, and pore size distribution for the Zr(IV), Sn(IV), and Ti(IV) oxyhydrates and double hydrates of the composition M _x Mn_1?x O _y ·nH₂O and M _x Al1_?x O _y ·nH₂O [M = Zr(IV), Sn(IV), Ti(IV), x = 0.5–0.9 were calculated. The specific surface charge and zero-charge point in 0.12 M KNO₃ were determined.     

Influence of Ca2+ substitution on thermal,structural, and conductivity behavior of Bi1−xCaxFeO3−y (0.40 ≤ x ≤ 0.55)

Bi_1?xCa_xFeO_3?y (0.40 ≤ x ≤ 0.55) perovskite oxides have been synthesized by solid-state reaction method to study their properties as a cathode material for intermediate temperature solid oxide fuel cells. The as prepared samples were characterized by X-ray diffraction, differential thermal analyzer/thermogravimetry, dilatometer, and impedance spectroscopy to study their structural, thermal, and electrical properties. The Rietveld refinement results confirmed that all the samples exhibit tetragonal structure with P4mm space group. In addition to this, sample x = 0.55 exhibits Ca₂Fe₂O₅ as a secondary phase. It has been observed that lattice parameters decrease with increase in calcium content. The thermal expansion coefficient and ionic conductivity increases with increase in calcium content up to x = 0.50. The highest ionic conductivity is observed for Bi_0.5Ca_0.5FeO_3?y i.e. 1.71 × 10^?2 S cm^?1.     

Sol–gel synthesis,crystal structure,surface morphology,and optical properties of Eu2O3-doped La2Mo3O12 ceramic

In this paper, we report the synthesis of the La–Mo–O tartrate gel precursors with the initial composition for La₂Mo₃O₁₂ ceramic prepared from different starting materials by an aqueous sol–gel synthesis route using tartaric acid as a complexing agent. Moreover, the La–Mo–O carbonate–tartrate and nitrate–tartrate gel precursors doped with x % of Eu₂O₃ (x = 0.5, 1.0, 2.0, 4.0, and 8.0) by aqueous sol–gel synthesis method were also prepared. The thermal decomposition of both the La–Mo–O carbonate–tartrate and nitrate–tartrate gels, which is the critical stage of this preparation technique, is investigated in detail. X-ray diffraction, scanning electron microscopy, and ultraviolet–visible spectroscopy were used for the determination of crystal structure, surface morphology, and optical properties of the La–Mo–O:xEu₂O₃ samples annealed at 400, 500, 600, 700, 800, 900, and 1,000 °C temperatures, respectively. The obtained results show that the thermal decomposition of the La–Mo–O tartrate gel precursors has occurred in a separate manner. The differences that came up during the thermal treatment of La–Mo–O tartrate gels have related only with the initial composition that determined the different crystallization ways of final compounds. Besides, the dopant concentration mainly influences the size of obtained particles and agglomeration of synthesized final materials. The initial composition of the La–Mo–O gel precursors has significant influence on the formation of final crystal phases at relatively lower temperatures than was expected according to the TG–DTA measurements. Finally, the optical properties of La–Mo–O tartrate gel precursors annealed at 500 °C depend on the nature of the initial compounds, which were used during the aqueous sol–gel process.     

Chelating behavior, thermal studies and biocidal efficiency of tioconazole and its complexes with some transition metal ions

New seven metal complexes of tioconazole drug with the general formulae [MCl₂(L)₂(H₂O)_x].yH₂O (where, x = 0 and y = 1 for M = Mn(II) or x = 2, y = 2 for M = Co(II)), and x = 0, y = 3 for M = Cu(II), Ni(II), Zn(II)) and [MCl₂(L)₂(H₂O)₂]Cl.3H₂O (where M = Cr(III) and Fe(III)) have been prepared and characterized based on elemental analyses, IR, magnetic moment, molar conductance, and thermal analyses techniques. From molar conductance data bivalent metal chelates are non-electrolytes while Cr(III) and Fe(III) chelates are electrolytes and of 1:1 type. According to the IR spectral data, TCNZ is coordinated to the metal ions in a neutral unidentate manner with N donor site of the imidazole–N. All the complexes are octahedral except Mn(II) complex has tetrahedral structure. TCNZ drug and its metal complexes were also screened for their biological activity.     

In situ crystalline investigation of sol–gel deposited barium stannate (Ba<Subscript>x</Subscript>SnO<Subscript>2+y</Subscript>; x:y ≈ 1:1) nanoparticles in alkaline medium

Fine layers of barium stannate nanoparticles have been synthesized by sol–gel technique with tin chloride pentahydrate (SnCl₄·5H₂O) and barium sulphate (BaSO₄). Physico-chemical properties of barium stannate, Ba_xSnO_2+y; x:y ≈ 1:1 were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and UV–Visible spectrophotometry technique. A growth mechanism based on the combination of particle sticking and molecule level heterogeneous growth is proposed. It has been found that the particle size of all the samples was distributed in the range 3.0–6.5 ? while optical absorption spectrum indicates that Ba_xSnO_2+y nanoparticles have a direct band gap of 3.9 eV.     

Synthesis of VO2 Nanopowders. Part II. Hydrolysis of Vanadium Alkoxide/Citric Acid Premixes: VO2 Nanostructures of Controlled Shape

Reaction of VO(OiPr)₃/citric acid premixes with excess water produces stable, blue dispersions of V_xO_y gel nanoparticles (5–100 nm in diameter) that can be isolated via acetone precipitation. Annealing under reducing conditions transforms these gel particles into crystalline, faceted VO₂ nanoparticles of similar size. Larger V_xO_y gel particles (75–200 nm in diameter) form when V_xO_y nanogel dispersions are aged with aqueous ammonia. Upon annealing, these larger gel particles transform into crystalline VO₂ rods of 50 nm–10 μm in length. Hysteresis loops confirming a semiconductor-to-metal phase transition near 68 °C expected for crystalline VO₂ particles are recorded by variable-temperature electrical resistance and powder X-ray diffraction measurements.     

Thermal stability and band gap study of heavy metal oxy-sulfide glass system

Novel oxy-sulfide glass system xPbS-(73 ? x) Bi₂O₃–27B₂O₃ with 6.06 ≤ x ≤ 36.35 named lead sulfide bismuth borate (LSBB) was prepared using normal melt and quench-casting technique. Phase transition temperatures t _g, t _x, t _pi, and t _l were noted from the DTA curves. Glass transition temperature t _g varied from 306 ± 2 to 336 ± 2 °C and the onset of crystallization temperatures t _x was between 331 ± 2 and 402 ± 2 °C. The glasses melted in the range 523 ± 2 to 597 ± 2 °C. The ratio t _g /t _l showed that compositions reported conform to the two-third law of glass formation. Hruby’s coefficient H _r witnessed the thermal stability of the system and that LSBB4 was most stable and glass formability factor k _gl showed that composition LSBB1–LSBB6 can easily corroborate vitreous state. The direct band gap energy varied from 1.56 to 3.07 eV, while indirect band gap energy for the fundamental absorption edge was 0.21–1.31 eV. Absorption edges obeyed Urbach rule. A broad range of band tailing was exhibited confirming amorphous state of the system.     

Glass-ceramic nanocomposites in the [(1 − x)PbO–xBaO]–Na2O–Nb2O5–SiO2 system: Crystallization and dielectric performance

The crystallization process, microstructure and dielectric properties of [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ (PBNNS) (0 ≤ x ≤ 1) glass-ceramics prepared by controlled crystallization were investigated. The crystallization strategies for acquiring nano-crystallized PBNNS glass-ceramics were monitored by differential thermal analysis (DTA). X-ray diffraction (XRD) analysis revealed a major crystal phase transition in PBNNS glass matrix as the crystallization temperature increased. At low temperatures (700–750 °C), the major crystal phases precipitating in the glass matrix are identified as Pb₂Nb₂O₇ for x = 0, Ba₂NaNb₅O₁₅ for x = 1 and their solid solution for 0.2 ≤ x ≤ 0.8; while at higher temperatures (≥850 °C), heat treatment produces different crystalline phases, PbNb₂O₆ and NaNbO₃ for x = 0, Ba₂NaNb₅O₁₅ and NaNbO₃ for x = 1, and the solid solution of these three phases for 0.2 ≤ x ≤ 0.8. Corresponding to the result of phase transition, microstructural observation proves increasing crystallite sizes with increasing temperature of heat treatment. At different crystallization temperatures, the dielectric properties of the [(1 − x)PbO–xBaO]–Na₂O–Nb₂O₅–SiO₂ glass-ceramics show a strong dependence on the chemical composition x. At low temperatures (700–750 °C), a maximum of the dielectric constant of the PBNNS glass-ceramic is found for the composition x = 0.6; while at higher crystallization temperatures (≥850 °C), the dielectric constants of all samples (0 ≤ x ≤ 1) exhibit decreasing values with increasing x.     

Effects of lutetium doping on the X-ray-excited luminescence properties of the tungstate Zn<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Lu<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>WO<Subscript>4</Subscript>

Polycrystalline samples in the lutetium-doped zinc tungstate system Zn_1?x Lu _x WO₄ with 0 ≤ x ≤ 0.08 were synthesized using the coprecipitation method followed by thermal treatment at 1000 °C during 4 h. The polycrystalline samples were characterized by X-ray diffraction analysis, scanning electron microscopy (SEM), infrared spectroscopy, and luminescence analysis under X-ray excitation. Rietveld analyses were performed. The variation of the wolframite structure cell parameters in the range 0 ≤ x ≤ 0.05 were congruent with substitution of Zn²⁺ by Lu³⁺. SEM micrographs of the obtained samples presented improved crystallization with morphology depending on the lutetium fraction. The luminescence spectra obtained under X-ray excitation (E < 40 keV) were in the blue–green region, and their intensity increased with x up to x = 0.05. The differences in the intensities of the X-ray luminescence spectra could be related to additional cation vacancies resulting from substitution of Zn²⁺ by Lu³⁺.     

New insights into the bioactivity of SiO2–CaO and SiO2–CaO–P2O5 sol–gel glasses by molecular dynamics simulations

The structures of binary xCaO · (100 ? x)SiO₂ glasses with x = 10, 20 and 30 mol-% and ternary (20 ? x)CaO · xP₂O₅ · 80SiO₂ glasses with x = 3, 10, 15, 17 and 20 mol-% have been studied by means of classical molecular dynamics simulations using both the melt-quenched and the sol–gel protocols. The structural picture derived correlates the bioactive behaviour to the combined effects of the connectivity of the extended silicate network and to the tendency to form (or not to form) non-homogeneous domains. In this context, a mathematical relationship that relates the Ca/P ratio in the Ca phosphate micro-segregation zones to the P₂O₅ content in ternary glasses has been developed and this has been used to fine-tuning the optimum amount of P in a glass for its highest in vitro bioactivity. The composition with optimal Ca/P ratio, 80Si–14.8Ca–5.2P, has been synthesized and the results of bioactivity tests have confirmed the prediction.     

Synthesis and fabrication of (1 − x)ZnAl2O4–xSiO2 thin films to be applied as patch antennas

Zinc aluminate compounds have been dispersed in silica matrix prepared by sol-gel method with different compositions for (1 ? x)ZnAl₂O₄–xSiO₂. Continuous stirring of ethylene glycol solution contained zinc nitrate, aluminium nitrate and silicon dioxide to produces gel precursor. Structural and morphological studies of (1 ? x)ZnAl₂O₄–xSiO₂ thin films were examined by field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) analysis. The FESEM images showed the spherical structures with porosity for (1 ? x)ZnAl₂O₄–xSiO₂ thin films. XRD analysis indicated that the crystallite size for (1 ? x)ZnAl₂O₄–xSiO₂ increased from 39.79 to 44.34 nm. Fourier transform infra-red analysis showed that the existence of H₂O molecules and the presence of nitrate group within the samples. Dielectric permittivity (ε _r ) of (1 ? x)ZnAl₂O₄–xSiO₂ samples were measured within frequency range from 1 Hz to 1 MHz. The dielectric permittivity, ε _r decreased as frequency was applied to the sample. The performance of the patch antenna can be measured using return loss analysis. The highest result shows that the patch antenna resonated at frequency 3.46 GHz and gives ?14.25 dB return loss bandwidth.     

Crystal structures,site occupations and phase equilibria in the system V–Zr–Ge

The V–Zr–Ge system was studied for two isothermal sections at 900 and 1200 °C. Three ternary compounds VZrGe (tI12, I4/mmm, CeScSi-type), V_xZr_5?xGe₄ (oP36, Pnma, Sm₅Ge₄-type) and V_4+xZr_2?xGe₅ (oI44, Ibam, Si₅V₆-type) were structurally characterized. Optical microscopy and powder X-ray diffraction (XRD) were used for initial sample characterization and electron probe microanalysis (EPMA) of the annealed samples was used to determine the exact phase compositions. The variation of the cell parameters of the various ternary solid solutions with the composition was determined. The three ternary phases were structurally characterized by means of single crystal and powder XRD. While VZrGe is almost a line compound, V_xZr_5?xGe₄ (0.2 ≤ x ≤ 3.0) and V_4+xZr_2?xGe₅ (0.06 ≤ x ≤ 1.2) are forming extended solid solution ranges stabilized by differential fractional site occupancy of V and Zr on the metal sites.     

Low temperature carbon monoxide catalytic oxidation at the Pd/Ce–Zr–Al–Ox catalyst

The homogeneous chemical composition ceria–zirconia–alumina (Ce–Zr–Al–O_x) nano-alloy were successfully synthesized by surfactant-assisted parallel flow co-precipitation method and applied as supports for low temperature CO oxidation. The experiment conditions were studied in detailed. At 0.92 wt% Pd loading, 30,000 ppm CO could be completely oxidized to CO₂ at 30 °C at a WHSV of 4,380 ml g^?1 h^?1 over the Pd/Ce–Zr–Al–O_x (n_Ce:n_Zr = 3:1) catalyst. Pd/Ce–Zr–Al–O_x catalysts were systematical studied by mean of BET, XRD and TEM analysis. XRD characterization showed that zirconium element entered into cubic structure of ceria and leaded to structure distortion. Addition of aluminum increased specific surface area of ceria–zirconia solid solution substantially. The average pore diameter of Ce–Zr–Al–O_x support palladium catalysts were the key impact factor for CO oxidation. When the Pd/Ce–Zr–Al–O_x catalysts had highly dispersed palladium nanoparticles, large average pore diameter, suitable surface area and pore volume, the activity of CO oxidation was the best.     

Synthesis and electrochemical characterization of duo doped spinels (zinc and praseodymium) for use in lithium rechargeable batteries

LiMn₂O₄ and LiZn_xPr_yMn_2?x?yO₄ (x = 0.10–0.24; y = 0.01–0.10) powders have been synthesized by sol–gel method using palmitic acid as chelating agent. The synthesized samples have been subjected to thermo gravimetric and differential thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDAX). The sol–gel route bestows low calcination temperature, shorter heating time, high purity, good control over stoichiometry, small particle size, high surface area, good surface morphology and better homogeneity, The XRD patterns reveal high degree of crystallinity and better phase purity. SEM and TEM images exhibit nano-sized nature particles with good agglomeration. EDAX peaks of Zn, Pr, Mn and O have been confirmed in actual compositions of LiMn₂O₄ and LiZn_xPr_yMn_2?x?yO₄. Charge–discharge studies of pristine spinel LiMn₂O₄ heated at 850 °C delivers discharge capacity of 132 mA h g^?1 corresponding to columbic efficiency of 73 % during the first cycle. At the end of 10th cycles, it delivers maximum discharge capacity of 112 mA h g^?1 with columbic efficiency of 70 % and capacity fade of 0.15 mA h g^?1 cycle^?1 over the investigated 10 cycles. Inter alia, all dopants concentrations, LiZn_0.10Pr_0.10Mn_1.80O₄ exhibits the better cycling performance (1st cycle discharge capacity: 130 mA h g^?1 comparing to undoped spinel 132 mA h g^?1) corresponding to columbic efficiency of 73 % with capacity fade of 0.12 mA h g^?1 cycle^?1.     

Effect of niobium doping on physical, thermal, and spectral parameters of infrared transmitting BGO70 glasses

Heavy metal oxide glasses doped with 2d transition metal niobium were casted through normal melt-quench technique in the formula composition (100?x) [3Bi₂O₃–7GeO₂ (BGO70)]?xNb₂O₅ where 5 ≤ x ≤ 25. Experimentally measured values of density d _exp were 6.737–7.149 g/cc ± 0.06 %. Corresponding molar volume V _m exp had values 29.677–31.550 cc ± 0.04 %, V _pyc varied 32.28–34.71 cc ± 0.03 % and oxygen molar volume $ V_{{{\text{mO}}^{2-} }} $ increased linearly from 17.761 to 20.467 cc ± 0.06 %. Thermal coefficient of linear expansion was between 5.316 ± 0.001 × 10^?6 and 8.033 ± 0.001 × 10^?6 K^?1. Glass transition temperature T _g, onset of crystallization temperature T _x, and the stability factor ΔT were noted from DTA curves. Direct allowed energy gap E _g was between 1.809–2.988 eV and Urbach energy had value 0.32–1.49 eV. Maximum transmission efficiency was 74 % for glass BGO70-Nb10. FTIR spectra revealed that lattice vibration modes were active in 400–1,300 cm^?1 range. A modifying behavior was assigned to Nb⁵⁺ ion in the system.     

Biomimetic Synthesis of Metal Ion‐Doped Hierarchical Crystals Using a Gel Matrix: Formation of Cobalt‐Doped LiMn2O4 with Improved Electrochemical Properties through a Cobalt‐Doped MnCO3 Precursor

We have synthesized spinel type cobalt‐doped LiMn₂O₄ (LiMn_2?yCo_yO₄, 0≤y≤0.367), a cathode material for a lithium‐ion battery, with hierarchical sponge structures via the cobalt‐doped MnCO₃ (Mn_1‐xCo_xCO₃, 0≤x≤0.204) formed in an agar gel matrix. Biomimetic crystal growth in the gel matrix facilitates the generation of both an homogeneous solid solution and the hierarchical structures under ambient condition. The controlled composition and the hierarchical structure of the cobalt‐doped MnCO₃ precursor played an important role in the formation of the cobalt‐doped LiMn₂O₄. The charge–discharge reversible stability of the resultant LiMn_1.947Co_0.053O₄ was improved to ca. 12 % loss of the discharge capacity after 100 cycles, while pure LiMn₂O₄ showed 24 % loss of the discharge capacity after 100 cycles. The parallel control of the hierarchical structure and the composition in the precursor material through a biomimetic approach, promises the development of functional materials under mild conditions.     

Thermophysical properties of thorium–praseodymium mixed oxides

Thorium–Praseodymium mixed oxide solid solutions (Th_1?yPr_y)O_2?x (y = 0.15, 0.25, 0.4, 0.55) were prepared by co-precipitation method. These mixed oxides form single-phase fluorite solid solutions (fm3m). Heat capacity (C _p) measurements and lattice thermal expansion characteristics of these solid solutions were determined with differential scanning calorimeter in the temperature range of 298–800 K and high temperature X-ray diffractometer in the temperature range of 298–2,000 K, respectively. The C _p,₂₉₈ of (Th _1?yPr_y)O_2?x pertaining to the solid solutions with the compositions, y = 0.15, 0.25, 0.4, and 0.55, were found to be 65.2, 62.4, 60.1, and 57.1 J K^?1 mol^?1, respectively. The coefficients of lattice thermal expansion in the temperature range of 298–2,000 K of (Th_1?yPr_y)O_2?x for these solid solutions with the compositions y = 0.15, 0.25, 0.4, and 0.55 were found to be 16.97, 20.43, 25.63 and 30.82 × 10^?6 K^?1, respectively.     

Phase separation characteristics of (U,Nd)O2 solid solutions by high temperature oxidation

The phase separation characteristics of the Nd element from SIMFUEL (simulated spent fuel) by high temperature oxidation was investigated in terms of the temperature range between 1,150 and 1,300 °C and the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O₂ with x = 0.03, 0.037 and 0.09. The XRD and SEM results indicate that an increase of the heat treatment temperature increases the amount of the Nd-rich (U_1?y Nd _y )O_2+v phase, while decreasing that of the Nd-poor (U_1?z Nd _z )₃O_8?w phase after heat treatment. Since the solubility of Nd in the (U_1?z Nd _z )₃O_8?w phase was almost constant regardless of the heat treatment temperature, the decrease of the Nd concentration in the Nd-rich (U_1?y Nd _y )O_2+v phase with increasing heat treatment temperature seems to be due to a diffusion of the U ions from the Nd-poor (U_1?z Nd _z )₃O_8?w phase to the Nd-rich (U_1?y Nd _y )O_2+v phase. The phase separation ratio of Nd was not nearly affected by the heat treatment temperature, but was increased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00. However, the phase separation ratio of U was slightly decreased with an increase in the heat treatment temperature and was strongly decreased with an increase in the initial concentration of Nd (x) in the pellets of (U_1?x Nd _x )O_2.00.     

Anatase–rutile transformation at the synthesis of rutile pigments (Ti,Cr,Nb)O2 and their color properties

Synthesis of rutile pigments is based on solid state reaction and on Hedvall effect, i.e., phase transformation from anatase to rutile. Therefore, it is important to know the thermal behavior of these compounds (the temperature of this change). The goal was to prepare rutile pigments of type Ti_1?3xCr_xNb_2xO_2+x/2 by conventional solid state method from titanium dioxide TiO₂ (AV-01, anatase), to determine an influence of composition (x = 0, 0.05, 0.10, 0.20, 0.30, 0.50) and calcination temperature (850; 900; 950; 1,000; 1,050; 1,100; 1,150 °C) on color properties of these compounds and to analyze other starting compounds of titanium (hydrated anatase paste TiO₂·nH₂O, titanyl sulfate dihydrate TiOSO₄·2H₂O (VKR 611), hydrated sodium titanium oxide paste Na₂Ti₄O₉·nH₂O) and their reaction mixtures for x = 0.05 by simultaneous TG–DTA analysis. According to the highest chroma C of color, the optimal conditions for synthesis of these pigments are concentration x = 0.05 and calcination temperature 1,050 °C and higher. It was observed that initial temperature 760–830 °C is needful for a formation of rutile structure. This temperature is the lowest for hydrated Na₂Ti₄O₉ paste (760 °C) and similar for other starting compounds of titanium.