Synthesis and characterization of fine lithium niobate powders by sol‐ gel method

Lithium niobate (LN) nanocrystal powders were prepared by low‐temperature sol‐gel method. Dihydrate lithium acetate as lithium source, and niobium chloride as niobium source were used as starting materials. The gel and powders were characterized by thermogravimetry and differential scanning calorimetry (TG/DSC), X‐ray diffraction (XRD), transmission electronmicroscopy (TEM) and Fourier transform infrared (FTIR) spectra. The results show that when the gel was heat‐treated at 600°C, the fine LN nanocrystals with the size of 40‐60 nm were obtained, and the size of the powders become larger with the heat‐treated temperature increasing. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical studies on ZnO films prepared by sol‐gel method

A standard sol‐gel method was used to deposit ZnO thin films of suitable thickness on glass substrate.The optical characteristics of the visible to infrared range on thermal stress were critically observed. Morphological signature of the films was detected by X‐ray diffraction (XRD) and the crystallite size determined by Scherrer method from XRD data were consistent with grain size estimated from spectroscopic data through Meulenkamp equation. The optical band gap value from the transmission spectrum was found to corroborate with the existing works. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Preparation and characterisation of Ag incorporated Al2O3 nanocomposite films obtained by sol‐gel method

Sol‐gel route has been applied for a deposition of the thin films of aluminum oxide and Ag embedded in Al₂O₃ films. The films are spin‐coated on Si and quartz substrates with the film thickness of 120 nm. XRD analysis has been used for the determination of the film structure. FTIR spectroscopy is applied for studying vibrational properties of the obtained coatings. Optical characterization is done by UV‐VIS spectroscopy. The formation of Ag nanoparticles has been confirmed by XRD and optical data. The sol‐gel process is found to be useful technology for incorporation of Ag nanoparticles in the metal oxide matrices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of annealing temperatures on properties of sol‐gel grown ZnO‐ZrO2 films

Mixed ZnO‐ZrO₂ films have been obtained by sol‐gel technology. By using spin coating method, the films were deposited on Si and glass substrates. The influence of thermal annealings (the temperatures vary from 400 °C to 750 °C) on their structural properties has been studied. The structural behavior has been investigated by the means of XRD and FTIR techniques. The results revealed no presence of mixed oxide phases, the detected crystal phases were related to the hexagonal ZnO and to crystalline ZrO₂. The sol‐gel ZnO‐ZrO₂ films showed polycrystalline structure with a certain degree of an amorphous fraction. The optical transmittance reached 91% and it diminished with increasing the annealing temperatures. The optical properties of the sol‐gel ZnO‐ZrO₂ films, deposited on glass substrates are excellent with high transparency and better then those of pure ZrO₂ films, obtained at similar technological conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Growth and characterization of Nd,Yb – yttrium oxide nanopowders obtained by sol‐gel method

Nanopowders of Y₂O₃ pure, doped and codoped by Nd³⁺, Yb³⁺ were obtained by sol‐gel method. Solution with ethylene glycol was choosed as the proper solution where crystallites of powder with Nd and Yb dopants had the same size. Finally the one‐phased compounds of Y₂O₃ doped 0.5 at% Nd and 1, 2 or 4 at% Yb were obtained. Grain growth and their morphology were investigated in various temperature and time of heating. The changes of crystallite sizes and lattice constants in relation to the heating time and temperature for the composition Y₂O₃ doped 0.5 at% Nd and 2 at% Yb are presented. Y₂O₃ containing 0,5 at% of Nd exhibits intense luminescence bands centered at 920 nm, 1100 nm and 1360 nm whereas a single band at about 1020 nm appears in samples co‐doped with neodymium and ytterbium. Luminescence spectra recorded did not depend on the sample preparation procedure and size of grains. OH impurity affects critically the relaxation dynamics of luminescent ion in nanopowders. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Nd(III) and Yb(III) ions incorporated in Y4Al2O9 obtained by sol‐gel method: synthesis,structure, crystals and luminescence

The nanocrystalline powders of Y₄Al₂O₉ (YAM) pure and doped by Nd, Yb and codoped by Nd and Yb were obtained via modified sol‐gel method. These powders were characterized by X‐ray diffraction method, scanning electron microscopy and high resolution scanning electron microscopy, luminescence spectroscopy and differential thermal analysis (DTA). We obtained single phase powders of crystalline structure with average size 70 nm exhibiting interesting luminescent properties. Efficient non‐radiative energy transfer between Nd and Yb was found. DTA confirmed the phase transition at about 1400 °C. From these nanocrystalline powders, the crystals YAM:Yb, YAM:Yb,Nd were grown by micro‐pulling down technique. They were cracking during cooling owing to the phase transition. Luminescent properties of YAM:Nd,Yb crystals were identical with properties of corresponding nanopowders within experimental incertitude. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low‐temperature preparation of bismuth ferrite microcrystals by a sol‐gel‐hydrothermal method

Well‐crystallized pure perovskite bismuth ferrite (BiFeO₃) powders with various morphologies have been synthesized by a novel sol‐gel‐hydrothermal route for the first time, which combined the conventional sol‐gel process and the hydrothermal method. The as‐prepared samples were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), differential thermal analysis (DTA) and ferroelectric test system. The results revealed that the compositions, morphological and dimensional changes in bismuth ferrite samples synthesized by sol–gel–hydrothermal method strongly depend on the concentrations of mineralizer. Ferroelectric hysteresis loops are displayed in the BiFeO₃ samples. The bismuth ferrites were hydrothermally synthesized at as low a temperature as 180 °C, which is comparatively lower than that synthesized by the normal sol–gel route. The formation mechanism of the bismuth ferrite crystalline was also discussed. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystallographic,optical and magnetic properties of Co‐doped ZnO thin films synthesized by sol gel route

ZnO thin films with various Co doping levels (0%, 1%, 3%, 5%, 8%, respectively) have been synthesized by sol gel spin coating method on glass substrates. XRD and XPS studies of the films reveal that cobalt ions are successfully doped into ZnO crystal lattice without changing the hexagonal wurtzite structure. The morphologies are studied by SEM and AFM and show wrinkle network structures with uniform size distribution. With Co doping concentration increasing, the wrinkle network width decreases gradually. The transmittance spectra indicate that Co doping can effectively reduce the optical bandgap of ZnO thin films. Photoluminescence show that all samples have ultraviolet, violet and green emission. When Co doping concentration increases up to 5%, the intensity of violet emission is greatly increased and a strong deep blue emission centered at 439 nm appears. The ferromagnetism of all samples was observed at room temperature. The emission mechanisms and ferromagnetism origination are discussed in detail. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructural,optical and electrical properties of GeO2 thin films prepared by sol‐gel method

GeO₂ thin films were prepared by sol‐gel method on ITO/Glass substrate. The electrical and optical properties and the microstructures of these films were investigated with special emphasis on the effects of an annealing treatment in ambient air. The films were annealed at various temperatures from 500 °C to 700 °C. Structural analysis through X‐ray diffraction (XRD) and atomic force microscope (AFM) showed that surface structure and morphological characteristics were sensitive to the treatment conditions. The optical transmittance spectra of the GeO₂/ITO/Glass were measured using a UV‐visible spectrophotometer. All films exhibited GeO₂ (101) orientation perpendicular to the substrate surface where the grain size increased with increasing annealing temperature. The optical transmittance spectroscopy further revealed high transparency (over 70 %) in the wave range 400 – 800 nm of the visible region. At an annealing temperature level of 700 °C, the GeO₂ films were found to possess a leakage current density of 1.31×10^‐6A/cm² at an electrical field of 20 kV/cm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Controllable synthesis of TiO2 nanoparticles employing substrate/dielectrophoresis/sol‐gel

Due to size‐dependent catalytic selectivity, the size and special morphology are of great importance to applications of TiO₂. The synthesis method of size and morphology control has been in need of innovation. In this study, TiO₂ nanoparticles(TiO₂‐NPs) with well‐defined morphology and homogenous size were synthesized using a novel method, in which bamboo substrate, dielectrophoresis (DEP) technology and a sol‐gel process were combined(substrate/ DEP/ sol‐gel). Powder X‐ray diffraction (XRD) and scanning electron microscopy (SEM) techniques were used to characterize the TiO₂‐NPs. Further study showed that, with this combined method, the size and the uniformity of TiO₂‐NPs can be controlled by changing the voltage of DEP. The number and arrangement of TiO₂ nanorods can be controlled by changing the voltage. Substrate/ DEP/ sol‐gel proved to be an efficient way to form special morphologies of TiO₂‐NPs. A visible‐light catalytic activity experiment showed that among three preparation methods, the substrate/ DEP/ sol‐gel method made TiO₂‐NPs with the highest catalytic activity for degradation of methyl orange. TiO₂‐NPs produced by the DEP/ sol‐gel process presented higher catalytic activity than TiO₂‐NPs produced by only a sol‐gel process.     

Synthesis and characterization of doped lithium aluminate nanocrystalline particles by sol‐gel method

Nanocrystalline particles of Co²⁺doped lithium aluminate (Co²⁺:LAO) and Ni²⁺‐doped lithium aluminate (Ni²⁺:LAO) were synthesized by sol–gel method. The crystalline nature and particle size of the samples were characterized by X‐ray diffraction analysis (XRD). The morphology and the presence Co²⁺ and Ni²⁺ in the synthesized samples were analyzed by scanning electron microscope (SEM) and energy dispersive X‐ray analysis (EDAX). The presences of functional groups in the samples were analyzed using FT‐IR analysis. The optical absorbance of the synthesized samples were observed using UV absorption spectral analysis. The frequency dependent dielectric behaviour of the synthesized nano materials was analyzed. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Experimental and first‐principle investigation of Cu‐doped ZnO ferromagnetic powders

Zn_1‐xCu_x O powders were synthesized by using sol‐gel method. Electronic band structure and ferromagnetic properties of Zn_1‐xCu_x O powders were studied experimentally and theoretically. The simulations are based upon the Perdew‐Burke‐Ernzerhof form of generalized gradient approximation within the density functional theory. Zn_1‐xCu_x O shows dilute ferromagnetism, as a saturated magnetization of 0.9×10^‐3emu/g was observed for Zn_0.95Cu_0.05O powders. The strong p ‐d hybridization between Cu and its four neighbouring O atoms is responsible for the ferromagnetism. Comparing with ZnO whose Fermi level locates at the valence band maximum, the Fermi level of the Zn_1‐xCu_x O shifts upward into the valence band and hence the Zn_1‐xCu_x O system exhibits theoretically a p ‐type metallic semiconducting property. The Zn_1‐xCu_x O system may be a potential candidate in spintronics. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Sol‐gel synthesis of electrospun BaO/MnO nanocomposite fibers and their magnetic characterization

A new approach, combining in‐situ sol‐gel process with electrospinning, was used to prepare magnetic barium acetate/manganese acetate/poly (vinyl alcohol) (PVA) composite nanofibers. The composite gel was synthesized by sol‐gel method in the presence of 10 wt.% PVA aqueous solution. PVA was used as stabilizer and polymeric matrix. The resultant barium acetate/manganese acetate/PVA composite nanofibers were calcined at 1023 K for 5 h. This formed BaO/MnO nanocomposite crystalline fibers with average diameter less than 100 nm and were characterized with Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), Energy Dispersive X‐ray Analysis (EDAX), powder X‐ray diffractometer (XRD), UV‐Vis‐Spectroscopy (UV) and Vibrating Sample Magnetometer (VSM) respectively. These composite fibers exhibited a uniform cylindrical morphology, with the BaO/MnO nanoparticles implanted in the fibers. M‐H curves were obtained at 300 K and 20 K. From the M‐H curves, room temperature ferromagnetism was observed at 300 K. At low temperatures, the ferromagnetic behavior was masked by the paramagnetic behavior. The saturation magnetization at 300 K was found to be 0.004 emu /g and the saturation magnetization at 20 K was found to be 0.658 emu /g. The magnetization at 20 K was found to be very large and it was several times larger than at 300 K. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and structural characterisation of zinc oxide thin films prepared by sol‐gel process

Zinc oxide thin films have been prepared on different substrates by the sol‐gel method using 2‐methoxyethanol solution of zinc acetate dihydrate stabilized by monoethanolamine. The photoluminescence spectra of the films show the band‐edge and sub‐band transitions. The intensity of the band edge emission peak increases, while the intensity of the deep level emission peak decreases in the films coated on sapphire substrate. Transmittance spectra show that the films are transparent beyond 400 nm. The structural property of the films has been evaluated using X‐ray diffraction. The X‐ray peak intensity of the film (002) grown on sapphire substrate is higher than the films grown on glass and quartz substrates. The AFM images show improvement in the surface of the annealed films as compared to the as‐grown ZnO films coated on sapphire substrates. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

An X‐ray powder diffraction study of the microstructural evolution on heating 3:2 and 2:1 mullite single‐phase gels

Single‐phase gels with compositions 3Al₂O₃·2SiO₂ and 2Al₂O₃·SiO₂ were prepared by gelling mixtures of aluminium nitrate and tetraethylorthosilicate. Gels were fast heated at different temperatures between 900°C and 1600°C. The phase transformation and microstructural changes of both mullite precursor gels over the temperature range were followed by X‐ray powder diffraction (XRD), lattice parameter determination (LP), and scanning and transmission electron microscopies (SEM and TEM). The distribution of crystallite sizes and strains were determined by linewidth refinements of X‐ray diffraction patterns using the integral breadth method of Langford and the Warren‐Averbach analysis. XRD of both heated gels showed the formation of crystalline mullite single phase. Some amount of glassy phase coexisted with mullites at low temperatures, i. e. below 900°C. The compositional range of mullites formed on heating gels at temperatures between 900°C and 1600°C was dependent on the starting nominal composition of gels. SEM and TEM micrographs of both heated gels below 1200°C showed the formation of small, discrete, prismatic, well‐shaped nanocrystals in a very ordered arrangement. The size of these nanocrystals was dependant on the nominal composition of gels and increased on rising the heating temperature of gel precursors. The microstructural features obtained from linewidth refinement results of X‐ray diffraction patterns also allowed to suggest the formation of prismatic a little elongated nanocrystals at temperatures below 1200°C. Microstrain values were small and only displayed a relatively significant value for mullites processed at 900°C. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural and magnetic studies of Mn‐doped ZnO

The bulk samples of Mn‐doped ZnO were synthesized with the nominal compositions Zn_1‐xMn_xO (x = 0.02, 0.05, 0.10, 0.15) by the solid‐state reaction and sol‐gel methods. In both the methods the samples were finally sintered at ∼700 °C in air. The X‐ray diffraction (XRD) studies of the samples synthesized by the solid‐state reaction method exhibit the presence of wurtzite (hexagonal) crystal structure similar to the parent compound (ZnO) in all the samples, suggesting that doped Mn ions sit at the regular Zn sites. However, same studies spread over the samples with Mn content ≥5% and synthesized by the sol‐gel method reveal the occurrence of some secondary phase in addition to the majority wurtzite phase. The magnetic measurements by vibrating sample magnetometer (VSM) clearly indicate ferromagnetic interaction at room temperature in all the samples. The Curie temperatures (T_c) and magnetization vary with concentration of Mn ions in the samples. However, the samples synthesized by sol‐gel method were found to have lower Tc values and also lower magnetization as compared to the corresponding samples synthesized by solid‐state reaction method. It could possibly be due to the presence of antiferromagnetic islands and smaller crystallite sizes in the samples prepared by sol‐gel method. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural properties of Zn1–xMgxO nanomaterials prepared by sol‐gel method

The mixed oxides Zn_1‐xMg_xO (ZMO) were prepared as nano‐polycrystalline powders and thin films by a simple sol–gel process and dip coating method. Thermogravimetric (TG) and differential thermal analysis (DTA) were used to study the thermal chemistry properties of dried gel. Structural and microstructural analysis was carried out applying x‐ray diffraction (XRD) and Rietveld method. Analysis showed that for x < 0.25, Mg replaces Zn substitutionally yielding ZMO single phase, while for x ≥ 0.25 two phases are identified ZMO and MgO. Replacing Zn²⁺ by Mg²⁺ distorts the cation tetrahedrons and decreases the lattice constants ratio c/a of the wurtzite ZMO which deviate the lattice gradually from the hexagonal structure as Mg⁺² increases. These distortions are attributed to the difference in electronic configuration of the two cations which suppress the paraelectric‐ferroelectric phase transition in the ZMO wurtzite. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Development of performance‐improved global positioning system (GPS) patch antenna based on sol‐gel‐synthesized dual‐phase (Bi4Ti3O12)X – (CaCu3Ti4O12)1–X composites

As a first attempt, a series of composite materials of general formula (Bi₄Ti₃O₁₂)_X – (CaCu₃Ti₄O₁₂)_1–X (BTO_X – CCTO_1–X) (X = 0–1.0) is synthesized by a sol‐gel combustion method. The phase changes, including their formation and evolution during the gradual substitution of BTO into CCTO are analyzed from the X‐ray diffraction pattern. The Jana2006 refinement plotting method proves that formation of an ideal dual‐phase composite system with separate orthorhombic and cubic phases occurs. A surface morphological study revealed that the BTO_X – CCTO_1–X composites are composed of small CCTO grains embedded in large BTO grains and both coexisted with a bimodal distribution. The possible vibrational modes of interactions between the constituent phases are determined from Raman spectra. Our inexpensive, combustion method for BTO_0.2 – CCTO_0.8 gives a high dielectric constant (ε′ = 3232) at 100 Hz at room temperature. The nature behind these data is revealed that the BTO‐CCTO composite can be applicable for the fabrication of miniaturized global positioning system (GPS) patch antennas. The fabricated GPS patch antenna shows optimum results of small size (2.37 mm × 1.18 mm), return loss (‐14.419) and wide bandwidth (350 MHz) to be operated at 1.57 GHz.     

放电等离子烧结镓掺杂氧化锌陶瓷及其电学特性研究

采用放电等离子烧结(SPS)方法烧结出了致密的掺镓氧化锌陶瓷(0.075wt; GZO).样品的烧结温度为950～1200℃,烧结时间为3～21 min,并对样品的物相、断口形貌、电学性能以及密度进行了测试和分析.结果表明,烧结条件对GZO的晶体结构没有影响,但是对样品的密度、晶粒尺寸、电阻率等性质有一定的影响.综合分析上述结果可得到用SPS方法烧结GZO陶瓷的最佳烧结工艺是烧结温度1100℃,烧结时间9 min.     

EDTA‐assisted synthesis of rose‐like ZnO architectures

Rose‐like ZnO nanostructures were prepared by a low‐temperature solution route with assistance of ethylenediaminetetraacetic acid disodium (EDTA‐2Na). The morphology of ZnO nanostructures was found to change from nanowire arrays to rose‐ and tower‐like architectures with increasing the molar ratio of EDTA‐2Na/Zn²⁺. Also, the shape evolution of ZnO nanostructures with time was observed from flat nanosheets to wrinkled nanosheets and to rose‐like nanostructures. EDTA‐2Na as a strong complexing agent was found to play a key role in the shape evolution. Photoluminescence spectra show that the rose‐like ZnO architectures have more defects than the nanowire arrays. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)