Magnetic properties of NiCuZn ferrite nanoparticles synthesized using egg-white

A new process to prepare single-phase nano-sized ferrites, Ni_0.8−xCu_0.2Zn_xFe₂O₄ with x = 0.1-0.7, was developed using egg-white precursors. TG measurement showed that, the precursors must be calcined at 550 °C. XRD patterns indicated the formation of single-phase cubic ferrites with particle size in the range 28.7-48.4 nm. TEM image gave particle size agrees well with that estimated using XRD. FT-IR spectroscopy showed the characteristic ferrite bands. Hysteresis loops measurements exhibited an increase in the saturation magnetization value (M_s) up to zinc content of 0.2 followed by unexpected decrease, which suggests the preference of Zn²⁺ ions to occupy octahedral sites. The decrease in the coercivity (H_c) with increasing zinc content is attributed to the lower magneto-crystalline anisotropy of Zn²⁺ ions compared to Ni²⁺ ions. Temperature dependence of the molar magnetic susceptibility (χ_M) suggested a ferrimagnetic behavior of the investigated samples and showed a decrease in the value of the Curie temperature (T_C) with increasing zinc.     

Synthesis and characterization of Ni1−xZnxFe2O4 spinel ferrites from tailored layered double hydroxide precursors

In this paper, a series of pure Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrites have been synthesized successfully using a novel route through calcination of tailored hydrotalcite-like layered double hydroxide molecular precursors of the type [(Ni + Zn)_{1 − x − y}Fe_y²⁺Fe_x³⁺(OH)₂]^x+(SO₄²⁻)_x/2·mH₂O at 900 °C for 2 h, in which the molar ratio of (Ni²⁺ + Zn²⁺)/(Fe²⁺ + Fe³⁺) was adjusted to the same value as that in single spinel ferrite itself. The physico-chemical characteristics of the LDHs and their resulting calcined products were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS) and Mössbauer spectroscopy. The results indicate that calcination of the as-synthesized LDH precursor affords a pure single Ni_1 − xZn_xFe₂O₄ (0 ≤ x ≤ 1) spinel ferrite phase. Moreover, formation of pure ferrites starting from LDHs precursors requires a much lower temperature and shorter time, leading to a lower chance of side-reactions occurring, because all metal cations on the brucite-like layers of LDHs can be uniformly distributed at an atomic level.     

Solvothermal synthesis of nanorods of ZnO, N-doped ZnO and CdO

ZnO nanorods with diameters in the 80-800 nm range are readily synthesized by the reaction of zinc acetate, ethanol and ethylenediamine under solvothermal conditions. The best products are obtained at 330 °C with a slow heating rate. Addition of the surfactant Triton^®-X 100 gave nanorods of uniform (300 nm) diameter. By adding a small amount of liquid NH₃ to the reaction mixture, N-doped ZnO nanorods, with distinct spectroscopic features are obtained. CdO nanorods of 80 nm diameter have been prepared under solvothermal conditions using a mixture of cadmium cupferronate, ethylenediamine and ethanol at 330 °C. Similarly, Zn_1−xCd_xO nanorods of a 70 nm diameter are obtained under solvothermal conditions starting with a mixture of zinc acetate, cadmium cupferronate, ethanol and ethylenediamine.     

Influence of isovalent ion substitution on the electrochemical performance of LiCoPO4

LiCo_1−xM_xPO₄ (M = Mg²⁺, Mn²⁺ and Ni²⁺; 0 ≤ x ≤ 0.2) compounds have been synthesized by solid-state reaction method and studied as cathode materials for secondary lithium batteries. LiCoPO₄ exhibits a discharge plateau at ∼4.7 V with an initial discharge capacity of 125 mAh/g and on cycling capacity falls. Substitution of Co²⁺ with Mg²⁺/Mn²⁺/Ni²⁺ in LiCoPO₄ has an influence on the initial discharge capacity and on cycling behaviour. The capacity retention of LiCoPO₄ is improved by manganese substitution. Among the manganese substituted phases, LiCo_0.95Mn_0.05PO₄ shows good reversible capacity of ∼50 mAh/g.     

Multifunctional Zn0.99−xMn0.01CuxS nanowires: Structure, luminescence and magnetism

The wurtzite-type Zn_0.99−xMn_0.01Cu_xS (x = 0, 0.003, 0.01) nanowires were prepared by a simple hydrothermal method at 180 °C. The structure and morphology of the samples were characterized by X-ray diffraction (XRD), X-ray absorption fine structure (XAFS), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), field emission scanning electron micrograph (FESEM) and X-ray photoelectron spectrum (XPS). The results showed that both the Mn²⁺ and Cu²⁺ ions substituted for the Zn²⁺ sites in the host ZnS. The ethylenediamine-mediated template was observed, which was used to explain the growth mechanism of the nanowires. The color-tunable emission can be obtained by adjusting the concentrations of Mn²⁺ and Cu²⁺ ions. The ferromagnetism was observed around room temperature.     

Synthesis of perovskite-type (La1−xCax)FeO3 (0 ≤ x ≤ 0.2) at low temperature

Gel formation was realized by adding citric acid to a solution of La(NO₃)₃·5H₂O, Ca(NO₃)₂·4H₂O, and Fe(NO₃)₂·9H₂O. Perovskite-type (La_1−xCa_x)FeO₃ (0 ≤ x ≤ 0.2) was synthesized by firing the gel at 500 °C in air for 1 h. The crystallite size (D_1 2 1) decreased with increasing x, while the specific surface area was 6.8-9.4 m²/g and independent of x. The XPS measurement of the (La_1−xCa_x)FeO₃ surface indicated that the Ca²⁺ ion content increased with increasing x, while the Fe ion content was independent of x. Catalytic activity for CO oxidation increased with increasing x.     

Microstructure and microwave dielectric characteristics of (1 − x)Ba(Zn1/3Ta2/3)O3-xBaTi4O9 ceramics

(1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ (0.1 ≤ x ≤ 0.85) composites are prepared by mixing 1150 °C-calcined BaTi₄O₉ with 1150 °C-calcined Ba(Zn_1/3Ta_2/3)O₃ powders. The crystal structure, microwave dielectric properties and sinterabilites of the (1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ ceramics have been investigated. X-ray diffraction patterns reveal that BaTi₄O₉, ordered and disordered Ba(Zn_1/3Ta_2/3)O₃ phases exist independently over the whole compositional range. The sintering temperatures of (1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ ceramics are about 1240 - 1320 °C and obviously lower than those of Ba(Zn_1/3Ta_2/3)O₃ ceramics. The dielectric constants (?_r) and the temperature coefficient of resonant frequency (τ_f) of (1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ ceramics increase with the increase of BaTi₄O₉ content. Nevertheless, the bulk densities and the quality values (Q × f) of (1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ ceramics increase with the increase of Ba(Zn_1/3Ta_2/3)O₃ content. The results are attributed to the higher density and quality value of Ba(Zn_1/3Ta_2/3)O₃ ceramics, the better grain growth, and the densification of sintered specimens added a small BaTi₄O₉ content. The (1 − x)Ba(Zn_1/3Ta_2/3)O₃-xBaTi₄O₉ ceramic with x = 0.1 sintered at 1320 °C exhibits a ?_r value of 31.5, a maximum Q × f value of 68500 GHz and a minimum τ_f value of 4.1 ppm/°C.     

Influence of thermal treatment on the structure and adsorption properties of layered zinc hydroxychloride

Layered zinc hydroxychloride (Zn₅(OH)₈Cl₂·H₂O) synthesized by hydrolyzing the ZnO particles in aqueous ZnCl₂ solutions at 100 °C for 48 h was outgassed at different temperatures ranging from 100 to 250 °C for 2 h and the structure and adsorption properties of the products were examined by various means. Outgassing at 100-150 °C eliminated the H₂O molecules in interlayer of zinc hydroxychloride. The layered structure of zinc hydroxychloride was disintegrated at 175 °C by breaking the OH?Cl hydrogen-bond in interlayer to form curled thin films composed of poorly crystallized β-Zn(OH)Cl and ZnO, leading to the increment of the specific surface area from 4 to 39 m²/g. The β-Zn(OH)Cl was decomposed at 225 °C to form ZnO. The crystallinity of ZnO was increased on elevating the outgassing temperature, giving rise to the UV absorption property. The H₂O and CO₂ adsorption measurements revealed that the zinc hydroxychloride outgassed at 100-150 °C possessed a high H₂O and CO₂ adsorption selectivity, and the selectivity diminished by the formation of thin films of ZnO above 175 °C.     

Ethanol-thermal synthesis of Cd1−xZnxS nanoparticles with enhanced photodegradation of 4-chlorophenol

Cd_1−xZn_xS nanoparticles were prepared by a one-pot solvothermal process from Zn(CH₃COO)₂, Cd(CH₃COO)₂ and NaS₂CNEt₂·3H₂O (sodium diethyldithiocarbamate, DDTC). The Cd_1−xZn_xS nanoparticles were characterized by X-ray powder diffraction, transmission electron microscope and high-resolution transmission electron microscope equipped with an energy-dispersive X-ray spectrometer. The absorption spectra of the Cd_1−xZn_xS nanoparticles can be tuned into visible region by modulating stoichiometric ratio between Zn and Cd. With the increase of Zn content, the Cd_1−xZn_xS nanoparticles showed an enhanced photocatalytic activity on degradation of 4-chlorophenol. The Cd_1−xZn_xS prepared under the optimal experimental condition (initial Zn/Cd = 3:1, 210 °C, 24 h, in ethanol) possessed the best photocatalytic activity. The conversion ratio could reach up to 84% after 12 h under irradiation of visible light for Cd_1−xZn_xS prepared in ethanol, which was obviously superior to those of products prepared in water. These results showed that both crystallinity and synthetic medium were responsible for the enhanced photocatalytic activity for 4-chlorophenol.     

Phase transformation of lithium tungsten bronzes, LixWO3, at room temperature ambient conditions

Samples of Li_xWO₃ with x = 0.05-0.7 were synthesized at 700 °C for 7 days using appropriate amounts of Li₂WO₄, WO₃ and WO₂ in evacuated sealed silica tubes. The products reveal different phases of perovskite tungsten bronze (PTB). An interesting phenomenon observed for the PTB phases is the gradual change in colours when they are exposed at room temperature ambient conditions (in air). This effect has been investigated using X-ray powder diffraction, infrared absorption and optical reflectivity methods for the powdered samples before and after 30 and 90 days in air. The spectra of the samples with x = 0.25-0.5 are dominated by a peak with maximum around 16,000 cm⁻¹ in the Kubelka Munk spectra which is related to the cubic Li_xWO₃ phase. The peak intensity increases with increasing x. After 30 days of exposure in air this peak disappeared for x < 0.5 samples due to a diffusion of Li from Li_xWO₃. X-ray and IR data show a gradual transformation into the lower symmetric phases (PTB_cubic ⇒ PTB_tetragonal ⇒ PTB_orthorhombic ⇒ PTB_monoclinic). The results suggest that Li is attracted by O₂ to the surface forming Li₂O which further reacts with H₂O and CO₂ in air. The in air altered samples regain their original colour when reheated at 500 °C in vacuum.     

Influence of Er doping on microstructure of oxyfluoride glass-ceramics

Oxyfluoride glasses with composition of 45SiO₂·20Al₂O₃·30PbF₂·5ZnF₂ by molar ratio with a high stability against crystallization have been obtained by melt quenching. After doping with x (x = 1, 2, 4) mol% of Er³⁺ transparent or translucent glass-ceramics could be formed. The structural transformations of these materials were investigated by thermal analysis, X-ray diffraction (XRD), transmission electron microscopy (TEM) and energy dispersive X-ray spectroscopy (EDS). Spherical polycrystalline aggregates comprised of many nanosized and randomly oriented β-PbF₂ grains were embedded separately among glassy matrix. On heating these nanosized grains merge with their neighbors to form bigger single crystals in a way like Ostwald ripening. The size modification of polycrystalline aggregates in the samples was found to be dependent on Er³⁺ doping.     

Oxygen vacancy ordering in strontium doped rare earth cobaltate perovskites Ln1−xSrxCoO3−δ (Ln = La, Pr and Nd; x > 0.60)

A family of Sr-doped perovskite compounds Ln_1−xSr_xCoO_3−δ (Ln = La³⁺, Pr³⁺ and Nd³⁺; x > 0.60), were prepared by sol-gel chemistry and reaction at 1100 °C under 1 atm of oxygen. This structural family has been shown to be present only for rare earth ions larger than Sm³⁺ and an upper limit of Sr²⁺ solubility in these phases was found to exist between x = 0.90 and 0.95. X-ray diffraction shows oxygen-deficient, simple cubic (Pm-3m) perovskite crystal structures. The combination of electron and powder neutron diffraction reveals that oxygen vacancy ordering occurs, leading to a tetragonal (P4/mmm) superstructure and a doubling of the basic perovskite unit along the crystallographic c-axis. No additional Ln³⁺/Sr²⁺ cation ordering was observed.     

Order-disorder phase transitions and high-temperature oxide ion conductivity of Er2+xTi2−xO7−δ (x = 0, 0.096)

The Er_2+xTi_2−xO_7−δ (x = 0.096; 35.5 mol% Er₂O₃) solid solution and the stoichiometric pyrochlore-structured compound Er₂Ti₂O₇ (x = 0; 33.3 mol% Er₂O₃) are characterized by X-ray diffraction (phase analysis and Rietveld method), thermal analysis and optical spectroscopy. Both oxides were synthesized by thermal sintering of co-precipitated powders. The synthesis study was performed in the temperature range 650-1690 °C. The amorphous phase exists below 700 °C. The crystallization of the ordered pyrochlore phase (P) in the range 800-1000 °C is accompanied by oxygen release. The ordered pyrochlore phase (P) exists in the range 1000−1200 °C. Heat-treatment at T ≥ 1600 °C leads to the formation of an oxide ion-conducting phase with a distorted pyrochlore structure (P2) and an ionic conductivity of about 10⁻³ S/cm at 740 °C. Complex impedance spectra are used to separately assess the bulk and grain-boundary conductivity of the samples. At 700 °C and oxygen pressures above 10⁻¹⁰ Pa, the Er_2+xTi_2−xO_7−δ (x = 0, 0.096) samples are purely ionic conductors.     

Synthesis and characterization of a new layered magnesium zinc phosphate hydrate

A new layered magnesium zinc phosphate hydrate, MgZn(HPO₄)₂·H₂O, with a zinc phosphate framework isostructural with the one of Na₂Zn(HPO₄)₂·4H₂O, was prepared by the direct ambient pressure and temperature reaction between zinc 2,4-pentanedionate, phosphoric acid and hexahydrated magnesium chloride. The as-prepared sample is monoclinic (a = 8.780(7) Å, b = 13.240(7) Å, c = 11.123(0) Å and β = 116.21(2)°). The prepared solid undergoes two thermal transformations when it is heated from 110 to 600 °C. The first transformation is due to the release of intercalated water molecules and the second one is due to the HPO₄²⁻ → P₂O₇⁴⁻ transition.     

Acceptor doping of Ln2Ti2O7 (Ln = Dy, Ho, Yb) pyrochlores with divalent cations (Mg, Ca, Sr, Zn)

New LANTIOX high-temperature conductors with the pyrochlore structure, (Ln_1−xA_x)₂Ti₂O_7−δ (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn; x = 0, 0.01, 0.02, 0.04, 0.07, 0.1), have been prepared at 1400-1600 °C using mechanical activation, co-precipitation and solid-state reactions. Acceptor doping in the lanthanide sublattice of Ln₂Ti₂O₇ (Ln = Dy, Ho, Yb) with Ca²⁺, Mg²⁺ and Zn²⁺ increases the conductivity of the titanates except in the (Ho_1−xCa_x)₂Ti₂O_7−δ system, where the conductivity decreases slightly at low doping levels, x = 0.01-0.02. The highest conductivity in the (Ln_1−xA_x)₂Ti₂O_7−δ (Ln = Dy, Ho, Yb; A = Ca, Mg, Zn) systems is offered by the (Ln_0.9A_0.1)₂Ti₂O_7−δ and attains maximum value for (Yb_0.9Ca_0.1)₂Ti₂O_6.9 and (Yb_0.9Mg_0.1)₂Ti₂O_6.9 solid solutions:∼2 × 10⁻² and 9 × 10⁻³ S cm⁻¹ at 750 °C, respectively. Ca and Mg are best dopants for Ln₂Ti₂O₇ (Ln = Dy, Ho, Yb) pyrochlores. Using impedance spectroscopy data, we have determined the activation energies for bulk and grain-boundary conduction in most of the (Ln_1−xA_x)₂Ti₂O_7−δ (Ln = Dy, Ho; A = Ca, Mg, Zn) materials. The values obtained, 0.7-1.05 and 1-1.4 eV, respectively, are typical of oxygen ion conductors. We have also evaluated defect formation energies in the systems studied.     

The effect of Cu content on the structure of Ni1−xCuxFe2O4 spinels

A series of Ni_1−xCu_xFe₂O₄ (0 ≤ x ≤ 0.5) spinels were synthesized employing sol-gel combustion method at 400 °C. The decomposition process was monitored by thermal analysis, and the synthesized nanocrystallites were characterized by X-ray diffraction, transmission electron microscopy, infra-red and X-ray photoelectron spectroscopy. The decomposition process and ferritization occur simultaneously over the temperature range from 280 °C to 350 °C. TEM indicates the increase of lattice parameter and particle size with the increase of copper content in accordance with the XRD analysis. Cu²⁺ can enter the cubic spinel phase and occupy preferentially the B-sites within x = 0.3, and redundant copper forms CuO phase separately. A broadening of the O 1s region increases with the increment of copper content compared to pure NiFe₂O₄, showing different surface oxygen species from the spinel and CuO. Cu²⁺ substitution favors the occupancy of A-sites by Fe³⁺.     

Synthesis and Li ion conductivity of Li2O-Nb2O5-P2O5 glasses and glass-ceramics

Glasses with the compositions of xLi₂O-(70 − x)Nb₂O₅-30P₂O₅, x = 30-60, and their glass-ceramics are synthesized using a conventional melt-quenching method and heat treatments in an electric furnace, and Li⁺ ion conductivities of glasses and glass-ceramics are examined to clarify whether the glasses and glass-ceramics prepared have a potential as Li⁺ conductive electrolytes or not. The electrical conductivity (σ) of the glasses increases monotonously with increasing Li₂O content, and the glass of 60Li₂O-10Nb₂O₅-30P₂O₅ shows the value of σ = 2.35 × 10⁻⁶ S/cm at room temperature and the activation energy (E_a) of 0.48 eV for Li⁺ ion mobility in the temperature range of 25-200 °C. It is found that two kinds of the crystalline phases of Li₃PO₄ and NbPO₅ are formed in the crystallization of the glasses and the crystallization results in the decrease in Li⁺ ion conductivity in all samples, indicating that any high Li⁺ ion conducting crystalline phases have not been formed in the present glasses. 60Li₂O-10Nb₂O₅-30P₂O₅ glass shows a bulk nanocrystallization (Li₃PO₄ nanocrystals with a diameter of ∼70 nm) and the glass-ceramic obtained by a heat treatment at 544 °C for 3 h in air exhibits the values of σ = 1.23 × 10⁻⁷ S/cm at room temperature and E_a = 0.49 eV.     

Elastic properties and spectroscopic studies of fast ion conducting Li2OZnOB2O3 glass system

Glass systems of the composition xLi₂O-20ZnO-(80 − x)B₂O₃ where (x = 5, 10, 15, 20, 25 and 30 mol%) have been prepared by melt quenching technique. Elastic properties, ¹¹B MAS-NMR and IR spectroscopic studies have been employed to study the structure of Li₂O-ZnO-B₂O₃ glasses. Elastic properties have been investigated using sound velocity measurements at 10 MHz. Elastic moduli reveal trends in their compositional dependence. The bulk modulus and shear modulus increases monotonically with increase of BO₄ units, which increase the dimensionality of the network. ¹¹B MAS-NMR and IR spectra show characteristic features of borate network and compositional dependent trends as a function of Li₂O/ZnO concentration. The results are discussed in view of borate network and the dual structural role of Zn²⁺ ions. The results indicate that the Zn²⁺ are likely to occupy network-forming positions in this glass system.     

Influence of Mg-substitution on the physicochemical properties of calcium phosphate powders

Tricalcium phosphate based ceramics (TCP) are bioresorbable and thereby considered to be promising bone replacement materials. The differences in crystal structure between α and β-TCP phases gives rise for different dissolution rates in vitro and in vivo, which may alter the bioresorbable behavior of TCP ceramics. It is suggested that the addition of magnesium ions, which are also present in biological tissues, stabilizes β-phase to higher temperatures and thus enables the sintering of β-TCP at elevated temperatures compared to Mg free TCP.In this paper, Mg-substituted TCP, with the general formula (Ca_1−xMg_x)₃(PO₄)₂ and 0.01 ≤ x ≤ 0.045, were produced by wet chemical synthesis from Ca(OH)₂, H₃PO₄ and MgO, after calcinations at three different temperatures between 750 and 1050 °C. The influence of different amounts of Mg substitution on the physical properties, microstructure, and sintering behavior of calcium phosphate powders was evaluated. Thermal analytical techniques, together with X-ray diffraction analysis, were successfully combined in order to characterize the occurring phase transformations during annealing of the powders. The results show that the addition of small amounts of Mg (up to 1.5 mol%) are adequate to postpone the β-α TCP phase transformation to 1330 °C and to accelerate the densification process during sintering of β-TCP ceramics.     

Thermal, spectroscopic and magnetic properties of the CoxNi1−x(SeO3)·2H2O (x = 0, 0.4, 1) phases: Crystal structure of Co0.4Ni0.6(SeO3)·2H2O

The Co_xNi_1−x(SeO₃)·2H₂O (x = 0, 0.4, 1) family of compounds has been hydrothermally synthesized under autogeneous pressure and characterized by elemental analysis, infrared and UV-vis spectroscopies and thermogravimetric and thermodiffractometric techniques. The crystal structure of Co_0.4Ni_0.6(SeO₃)·2H₂O has been solved from single-crystal X-ray diffraction data. This phase is isostructural with the M(SeO₃)·2H₂O (M = Co and Ni) minerals and crystallizes in the P2₁/n space group, with a = 6.4681(7), b = 8.7816(7), c = 7.5668(7) Å, β = 98.927(9)° and Z = 4. The crystal structure of this series of compounds consists of a three-dimensional framework formed by (SeO₃)²⁻ selenite oxoanions and edge-sharing M₂O₁₀ dimeric octahedra in which the metallic cations are coordinated by the oxygens belonging to both the selenite groups and water molecules. The diffuse reflectance spectra show the essential characteristics of Co(II) and Ni(II) cations in slightly distorted octahedral environments. The calculated values of the Dq and Racah (B and C) parameters are those habitually found for the 3d⁷ and 3d⁸ cations in octahedral coordination. The magnetic measurements indicate the existence of antiferromagnetic interactions in all the compounds. The magnetic exchange pathways involve the metal orbitals from edge-sharing dimeric octahedra and the (SeO₃)²⁻ anions which are linked to the M₂O₁₀ polyhedra in three dimensions.