Optical and electrical properties of p-type Ag-doped ZnO nanostructures

Zn_1−xAg_xO nanoparticles (NPs) (x=0, 0.02, 0.04, and 0.06) were synthesized by a sol–gel method. The synthesized undoped ZnO and Zn_1−xAg_xO-NPs were characterized by X-ray diffraction analysis (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and UV–visible spectroscopy. The XRD patterns indicated that undoped and Ag-doped ZnO crystallize in a hexagonal wurtzite structure. The TEM images showed ZnO NPs with nearly spherical shapes, with particle size distributed over the nanometer range. Evidence of dopant incorporation is demonstrated in the XPS measurements of the Ag-doped ZnO NPs. The Raman measurements indicated that the undoped and Ag-doped ZnO-NPs had a high crystalline quality. From the result of UV–vis, the band-gap values of prepared undoped and Ag-doped ZnO were found to decrease with an increase in Ag concentration. The obtained undoped and Ag-doped ZnO nanoparticles were used as a source material to grow undoped and Ag-doped ZnO nanowires on n-type Si substrates, using a thermal evaporation set-up. Two probe method results indicated that the Ag-doped ZnO nanowires exhibit p-type properties.     

Structural properties and hyperfine interactions in Co–Zn Y-type hexaferrites prepared by sol–gel method

Y-type barium hexaferrites Ba₂Co_2−xZn_xFe₁₂O₂₂ (0.0≤x≤2.0) were prepared using sol–gel method and then sintering at temperatures between 900 and 1100 °C. The properties of the prepared samples were investigated using X-ray diffraction, scanning electron microscopy, and Mössbauer spectroscopy. XRD patterns revealed the presence of a single Y-type hexaferrite phase in the samples sintered at temperatures above 1000 °C. Mössbauer data indicated that Co²⁺ ions occupied octahedral sites in the T blocks, while Zn²⁺ ions were distributed between the two tetrahedral sites. This trend for cationic distribution resulted in weakening the superexchange interactions between spin-up and spin-down sublattices with increasing Zn content, and a consequent reduction in the hyperfine fields in Zn rich compounds.     

Microwave hydrothermal synthesis of Sr doped ZnO crystallites with enhanced photocatalytic properties

Pure and Sr²⁺ doped ZnO crystallites were successfully synthesized via a microwave hydrothermal method using Zn(NO₃)₂·6H₂O and Sr(NO₃)₂·6H₂O as source materials. The phase and microstructure of the as-prepared Zn_1−xSr_xO crystallites were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Ultraviolet–visible spectrum (UV–vis) and photochemical reaction instrument were used to analyze the photocatalytic properties of the particles. XRD results show that the diffraction peaks of the as-prepared Zn_1−xSr_xO crystallites shifted slightly toward lower 2θ angle with the increasing of Sr²⁺ doping concentration from 0% to 0.3%. The pure ZnO crystallites with lamellar structure are found transforming to a hexagonal columnar morphology with the increase of Sr²⁺ doping concentration. UV–vis analysis shows that the particles have a higher absorption in UV region with a slightly decreased of optical band (E_g) gap. The photocatalytic activity of Sr²⁺ doped ZnO crystallites was evaluated by the Rhodamine B (RhB) degradation in aqueous solution under visible-light irradiation. Compared with the pure ZnO particles, the photocatalytic properties of the Sr²⁺ doped ZnO crystallites are obviously improved. The photocatalysis experiment results demonstrate that the 0.1% Sr²⁺ doped ZnO exhibits the best photocatalytic activity for the degradation of Rhodamine B.     

Hydrothermal synthesis of Li co-doped Zn0.98Mg0.02O nanoparticles and their structural,optical and electrical properties

Zn_0.98−xMg_0.02Li_xO (x=0.0, 0.01, 0.02, 0.03) nanoparticles were synthesized by the hydrothermal method. The structural, optical and electrical properties of the samples were analyzed by X-ray diffraction (XRD), Scanning Electron Microscope (SEM), Diffuse Reflectance UV–vis spectroscopy, and Hall effect measurements. XRD results showed that Zn_0.98−xMg_0.02Li_xO with wurtzite structure are obtained without impurities and additional phases. The lattice parameters (a, c) initially decrease, but they increase with further Li doping. The optical measurements exhibited blue-shift of optical band edge and widening of the band gap. Temperature dependent transport measurements using Van der Pauw method showed that Li doping increased the resistivities and charge carrier density, while it decreased the Hall mobility.     

Low-temperature preparation of lanthanum-doped BiFeO3 crystallites by a sol–gel-hydrothermal method

Multiferroic Bi_1−xLa_xFeO₃ (BLFO, x = 0, 0.15, 0.3, 0.4) powders were for the first time synthesized by a novel sol–gel-hydrothermal route. The as-prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and fourier transform infrared (FT-IR) spectroscopy. The XRD results indicated that pure BLFO crystallites could be obtained for x ≤ 0.3, and the phase purity was sensitive to the concentration of mineralizer. SEM results revealed that the morphology and dimension of the BLFO microspheres and submicrotiles could be effectively controlled by varying KOH concentrations. The formation mechanism of the BLFO crystalline was also discussed.     

One-step synthesis of Ni0.5Zn0.5Fe2O4 fine-patterned films via photosensitive sol–gel route

Ni_1−xZn_xFe₂O₄ (NZFO) (x=0.0–0.7) films were prepared by a photosensitive sol–gel route utilizing nickel acetate, zinc acetate and ferric nitrate as starting materials. The saturation magnetization of the NZFO film showed a parabolic tendency with Zn substitution. For Zn substitution of 0.5, the saturation magnetization reached the maximum value of 683 emu/cm³ with a relative low coercivity of 56 Oe at room temperature. The phase constituents and surface morphology of the films were characterized by X-ray diffractometer (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Through a direct patterning process, a fine-patterned Ni_0.5Zn_0.5Fe₂O₄ film was obtained by a photochemical reaction between the chelated complexes and UV light.     

Structural and magnetic properties of Co1−xZnxFe2O4 nanorods prepared by the solvothermal annealing method

Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods have been prepared by the thermal decomposition of the corresponding oxalate precursor, which was synthesized by the template-, surfactant-free solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometry (VSM). The obtained Co_1−xZn_xFe₂O₄ (0.1≤x≤0.9) nanorods were built by many nanoparticles with average sizes around 20 nm to form one-dimensional arrays. Vibrating sample magnetometry measurements show that the coercivity of the ferrite nanorods decreases with increasing Zn content, whereas the specific saturation magnetization initially increases and then decreases with the increase of Zn content. The maximum saturation magnetization value of the as-prepared sample (Co_0.5Zn_0.5Fe₂O₄) reaches 43.0 emu g⁻¹.     

Synthesis,structure and optical properties of x(CuO)/(1−x)Ni(OH)2 [x=0, 0.1 and 0.3] nanocomposites

The x(CuO)/(1−x)Ni(OH)₂ [x=0, 0.1 and 0.3] nanocomposites were prepared by the hydrothermal method in the presence of the surfactant polyethylenglycol-10000 (PEG-10000). X-ray diffraction (XRD), infrared (IR) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were used to characterize the as-prepared samples. The increase of the CuO content led to the increase of the crystallite size of both, the β-Ni(OH)₂ and the CuO. The increase in the crystallite size greatly affects the band gap energy of the as-prepared nanocomposites. The band gap energies of the x(CuO)/(1−x)Ni(OH)₂ nanocomposites were estimated by UV–vis spectroscopic method. UV–vis spectroscopic results showed an apparent decrease in the direct band gap energies. The x(CuO)/(1−x)Ni(OH)₂ [x=0, 0.1 and 0.3] nanocomposites show low band gap energies compared to the Ni(OH)₂ bulk materials. The enhanced optical properties lead to their possible use in photocatalytic and photovoltaic applications.     

Fabrication and characterisation of Cr and Co doped Bi1.5Zn0.92Nb1.5O6.92 pyrochlores

Cr and Co doped Bi_1.5Zn_0.92Nb_1.5O_6.92 pyrochlore ceramics were produced by solid state mixing of oxides. Cr and Co were doped into the Nb and Nb-Zn sites considering the compositions of Bi_1.5Zn_0.92Nb_1.5−xCr_xO_6.92−x, (Bi_1.5Zn_0.46)(Zn_0.46−3x/6Nb_1.5−3x/5Cr_x)O_6.92−x/2 for Cr doping and Bi_1.5Zn_0.92Nb_1.5−3x/5Co_xO_6.92, (Bi_1.5Zn_0.46)(Zn_0.46−3x/6Nb_1.5−3x/5Co_x)O_6.92−x/2 for Co doping. The solubility limit of Cr in BZN was higher than that of Co and the solubility limit increased when doping was made both into Nb and Zn sites. The second phases appeared when x > 0.2 for Cr and x > 0.15 for Co doping into the Nb-Zn sites. Simultaneous Cr doping into the Nb- and Zn-sites of BZN pyrochlore gave higher dielectric constant than doping into the Nb-site of pyrochlore. However, Co doping into the Nb- and Zn-sites and only into the Nb-site of BZN gave identical dielectric results in the range of 202-218. The temperature coefficient of dielectric constant decreased with Cr doping and increased with Co doping.     

Sintering behavior and electromagnetic properties of Fe-deficient NiZn ferrites

Sintering behavior and electromagnetic properties of Ni_0.5Zn_0.5Fe_2−xO_4−3/2x ferrite (x = 0, 0.4, 0.8) by the sol–gel method are investigated. Fe deficiency in the composition enhances sintering and retards grain growth. The near fully dense Fe-deficient samples could be obtained at a sintering temperature as low as 1120 °C and the highest relative density appears in the x = 0.8 sample sintered at 1150 °C. Second phase zincite ZnO resulting from Fe deficiency plays an important role in spinel NiZn ferrites by acting as a grain growth inhibitor and the grain growth of NiZn ferrite is effectively suppressed. When the sintering temperature is above 1200 °C, extensive grain growth occurs due to the probability of serious volatilization of zinc at high temperatures. The ratio of Ni to Zn of NiZn ferrites increases with increasing Fe deficiency due to the separation of zinc from spinel lattice, which results in the decrease in initial permeability and the increase in Curie temperature and resonant frequency.     

Blue pigments based on CoxZn1−xAl2O4 spinels synthesized by the polymeric precursor method

The Co_xZn_1?xAl₂O₄ system (x = 0; 0.1; 0.3; 0.5; 0.7; 0.9 and 1) was synthesized by the polymeric precursor method and characterized by the techniques XRD, TG-DTA, IR, UV–vis and colorimetry. The XRD patterns displayed the characteristic peaks of the spinel structure and a good crystallinity. The DTA curves showed an exothermic peak corresponding to the enthalpy of the transition taking place at about 700 °C. The infrared spectra displayed vibrations at about 650, 550, 540, 520, 500, 490 cm^?1, which were ascribed to the spinel structure. The UV–vis spectra presented three bands at 550, 580 and 620 nm attributed to the Co²⁺ spin transitions in tetrahedral sites. The colorimetric data point out the formation of blue pigments, corresponding to highly negative values of b¹. The lightness, coordinate L¹, increases with the heat treatment temperature. These facts reveal that Co_xZn_1?xAl₂O₄ is a promising system that can be employed to obtain ceramic blue pigments.     

Cobalt and nickel aluminate spinels: Blue and cyan pigments

M²⁺-doped aluminate spinels (M=Co or Ni) were prepared by a polymeric route leading to pure phases for synthesis temperatures equal to 800 or 1200 °C and characterized by UV–vis–NIR spectroscopy, ²⁷Al NMR and XRD refinements. Coloration of the synthesized pigments is clearly sensitive to the distribution of doping ions in the aluminate spinel lattice. As the synthesis temperature increased, a color shift from green to blue has been observed for Zn_1−xCo_xAl₂O₄ compound while coloration of Zn_1−xNi_xAl₂O₄ compound remains greenish-gray. Hence, to improve pigment coloration and/or synthesis cost, two different strategies have been proposed: (i) the synthesis of aluminum over-stoichiometric spinel with Zn_0.9Co_0.1Al_2.2O_4+δ formal composition in order to force Co²⁺ to be located in tetrahedral sites and (ii) changing from ZnAl₂O₄ to MgAl₂O₄ as host lattices for Ni²⁺ doping ions in order to force Ni²⁺ to be located in octahedral sites.     

Cd1−xZnxTe thin films formed by non-aqueous electrochemical route

Polycrystalline thin films of graded band gap ternary cadmium zinc telluride (Cd_1−xZn_xTe) have been electrodeposited in a non-aqueous bath onto an indium tin oxide (ITO) coated glass cathode. Ethylene glycol was used as the non-aqueous medium. The cathodic electrodeposition of the ternary semiconductor Cd_1−xZn_xTe was studied using cyclic voltammetry in conjunction with photovoltammetry, optical, compositional, structural measurements and surface morphology. It is shown that the band gap of this alloy can be tuned from 1.42 to 2.21 eV by controlling the Cd:Zn mole fractions. X-ray diffraction (XRD) and energy dispersive X-ray analysis (EDAX) measurements showed formation of Cd_1−xZn_xTe, where x varied between 0 and 1. It was found that the observed XRD reflections of all the samples index to the cubic phase of the Cd_1−xZn_xTe. The direction of the thermoemf developed in Cd_1−xZn_xTe films has also been shown to be opposite to the thermoemf for binary CdTe films. The resistivity rises with increase in the band gap indicating formation of a continuous solid solution of CdTe and ZnTe in the ternary phase Cd_1−xZn_xTe. The electrodeposited films have also been shown to possess polycrystalline pyramidal grains with compact and void free morphology.     

Study of cation distribution for Cu–Co nanoferrites synthesized by the sol–gel method

Nano sized polycrystalline soft ferrite particles with composition Cu_1−xCo_xFe₂O₄ (x =0.1, 0.3, 0.5, 0.7, 0.9) were synthesized by the sol–gel technique. The existence of well-defined single cubic spinel structure was confirmed in all the samples by X-ray diffraction. The crystallite size found by XRD varied from 14.8 to 34.0 nm. The microstructure was also characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Slight expansion of the unit cell was detected with the increase of Cobalt concentration, which may be attributed due to larger ionic radius of Co²⁺. Lattice parameter ranged from 8.34 Å to 8.37 Å for Co²⁺ from 0.1–0.9. The distribution of cations amongst A- and B-sites of the lattice was estimated by X-ray diffraction by using the R-factor technique. The results showed that both Cu²⁺ and Co²⁺ ions occupy mainly the B-site while Fe³⁺ ions were equally distributed among A- and B-sites. The data obtained from cation distribution analysis was used to determine the magnetic moment for each sample and VSM studies were also carried out to validate these calculations. Magnetic measurements showed that the saturation magnetization (Ms) and coercivity (Hc) increased with increasing cobalt content.     

Structural and magnetic evaluation of substituted NiZnFe2O4 particles synthesized by conventional sol–gel method

The aim of this study is to evaluate the structural and magnetic properties of Ni–Zn doped ferrite with trivalent Al³⁺ and Cr³⁺ cations substitution in Ni_0.6Zn_0.4Fe_2−xCr_x/2Al_x/2O₄ (x=0, 0.1, 0.2, 0.3, 0.4 and 0.5) synthesized by employing conventional sol–gel method. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FE-SEM), Mössbauer spectroscopy (MS) and vibrating sample magnetometer (VSM) analysis were carried out in order to characterize the structural and magnetic properties of particles. The XRD results confirmed the formation of single phase of spinel ferrite particles for a whole series of samples. The results of FTIR analysis indicated that the functional groups of Ni–Zn spinel ferrite were formed during the sol–gel process. Furthermore, FE-SEM micrographs revealed that the distribution of particles size is narrow. According to Mössbauer spectra,the doped cations are replaced in iron site occupancy of octahedral sites. It was found that with an increase in substitution contents magnetization decreased due to occupation of Al and Cr cations at low level substitutions in octahedral sites.     

Structural and magnetic properties of Pr–Ni substituted Ca0.5Ba0.5Fe12O19 hexa-ferrite nanoparticles

Effect of Pr–Ni substitution on structural and magnetic properties of Ca_0.5Ba_0.5−xPr_xNi_yFe_12−yO₁₉ (x=0.00–0.10 and y=0.00–1.00) prepared by the sol–gel auto combustion method were investigated. The XRD analysis confirmed the single phase M-type hexa-ferrite structure. The lattice parameters were found to increase as Pr–Ni content increases, which is attributed to the ionic size of the implicated cations. The Pr–Ni seems to be completely soluble in the lattice. Transmission electron microscopy reveals that the grain size decreases with increase of Pr–Ni substitution. The coercivity and remanent magnetization ranges from 1511 to 1925 (Oe) and 21.4 to 26.5 (emu/g), respectively. The coercivity values of all the samples fall in the range of M-type hexa-ferrites.     

Development of blue ceramic dyes from cobalt phosphates

In this study the development of blue ceramic dyes from compositions based on phosphate structures have been investigated. The replacement of cobalt by copper or iron to minimize the Co content have been considered. MFeO(PO₄) (M = Co, Cu) solid solutions have been obtained with Co_1−xCu_xFeOPO₄ (0 ≤ x ≤ 1) compositions prepared from gels and fired at 1000 °C/2 h. Co_1−xCu_xFeOPO₄ compositions are not indicated to minimize the Co content in ceramic dyes because they decompose in glazed samples and pinhole defect is obtained. From FeCoOPO₄–2FePO₄ compositions, Co₃Fe₄(PO₄)₆ structure introduces the Co²⁺ ions into glassy matrix and suitable blue materials are obtained. In the conditions of this study, optimal cobalt amount is about 10 wt% Co from Co_1−xFe_1+xO_1−x(PO₄)_1+x (x ≈ 0.6) compositions.     

Magnetic and dielectric properties of Zn substituted cobalt oxide nanoparticles

Zinc-substituted cobalt oxide nanoparticles (Zn_xCo_3-xO_4, 0 ≤ x ≤ 0.5) were produced by microwave refluxing technique. The structural, microstructural and magnetic properties of these samples were studied using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and magnetic property measurement system (MPMS) respectively. XRD and TEM analyses confirmed the single phase nature for all the samples. Rietveld analysis of the samples further confirmed the substitution of Zn-ions into the Co₃O₄ lattice. The chemical states of the elements were studied using X-ray photoelectron spectroscopy (XPS), which suggest the presence of Zn²⁺, Co²⁺, and Co³⁺ ions in the samples. The maximum saturation magnetization (M_S) values of 0.33 Am²/kg was obtained for x = 0.01 sample, and then it continuously reduced with increased Zn content. The dielectric property of the samples was studied in the frequency range of 40 Hz–110 MHz. The samples x = 0.05 and 0.5 displayed the lowest conductivity due to the narrow size distribution of grains.     

Magneto-optical properties of rare earth metals substituted Co-Zn spinel nanoferrites

Cobalt–zinc ferrite nanoparticles (NPs) substituted with three different metals, Co_0.5Zn_0.5Re_xFe_2-xO₄ (RE = Ce, Dy, and Y; 0.00?≤?x?≤?0.05) were prepared hydrothermally. Fourier Transform-Infrared (FT-IR) Spectroscopy, X-ray powder diffraction (XRD), Field-Emission Scanning Electron Microscope (FESEM) coupled with energy-dispersive X-ray spectroscopy (EDX) and Vibrating Sample Magnetometry (VSM) analyzed the products. The formation of cubic phase of spinel Co-Zn ferrite NPs were confirmed through XRD, FT-IR and FE-SEM techniques. The structural investigation of NPs by XRD revealed that the lattice parameter "a" decreases with the introduction of the RE in the ferrite structure by the substitution of Fe³⁺ by RE ions. The different magnetic parameters of Co_0.5Zn_0.5Re_xFe_2-xO₄ (RE = Ce, Dy, and Y; 0.00?≤?x?≤?0.05) NPs such as the saturation magnetization, coercivity, remanence, and magnetic moment were calculated and discussed in relation to structure and microstructure properties. M (H) hysteresis curves indicated that the samples exhibit superparamagnetic nature at room temperature. A slight improvement in the magnetization was obtained especially for the Ce- and Y-substituted Co_0.5Zn_0.5Fe₂O₄ (CZF) NPs at a certain RE level. However, the case Dy-substituted CZF products showed a sharp decrease in the magnetization with x?>?0.01. The results are mostly ascribed to the substitution of smaller Fe³⁺ ions with larger RE³⁺ ions.