Effect of Precursor Concentration on Physical Properties of Cube-Like Zn2SnO4 Powders Synthesized by Co-Precipitation Method

Cube-like Zinc stannate (Zn₂SnO₄) spinel powders were synthesized by co-precipitation method using chloride starting precursors of zinc and tin. The influence concentration of precursors on relevant physical properties of Zn₂SnO₄ was investigated by increasing concentration of precursor material at 0.1 to 0.4 M (Zn:Sn at ratio 1:1). Structural properties of as-synthesized and Zn₂SnO₄ crystal were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and X-ray absorption spectroscopy (XAS). The results indicate that as-prepared material without calcination process is in cubic symmetry of zinc hydroxy stannate (ZnSn(OH)₆) affirmed by SEM and XRD results. Meanwhile, spinel phase of Zn₂SnO₄ with strong crystalline and eminent cubic structure can be achieved after calcination at 1000°C. Homogenous dispersion, high crystallinity and good cubic structure of Zn₂SnO₄ powders are occurred at higher concentration of precursors. Moreover, the oxidation state of these samples were investigated by the Zn K-edge and Sn L3-edge X-ray absorption near edge structure (XANES) using the synchrotron radiation light source. The analyses of XANES spectra revealed that the oxidation state of Zn was +2 and Sn valence was +4 in all Zn₂SnO₄ samples, which well corresponds to the theoretical values.     

Synthesis, formation and characterization of lead zinc niobate–lead zirconate titanate powders via a rapid vibro-milling method

In this study, an approach to synthesizing pyrochlore-free lead zinc niobate – lead zirconate titanate powders with a formula xPb(Zn_1/3Nb_2/3)O₃–(1???x)Pb(Zr_1/2Ti_1/2)O₃ (when x?=?0.1–0.5) by a mixed oxide synthetic route via a rapid vibro-milling has been developed. The formation of perovskite phase in calcined PZN-PZT powders has been investigated as a function of calcination temperature by TG-DTA and XRD techniques. Powder morphology and chemical composition have been determined with SEM and EDX techniques. The potential of a vibro-milling technique as a significant time-saving method to obtain single-phase PZN-PZT powders at low calcination temperature is also discussed. The results indicate that at calcination condition of 900 °C for 2 h, with heating/cooling rates of 20 °C/min single-phase PZN-PZT powders can be obtained for every composition ratio between x?=?0.1–0.5.     

High temperature electrical characterization of nano-crystalline BaTiO3 synthesized using Ba(NO3)2 and TiO2

The reaction of Ba(NO₃)₂ with TiO₂ was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO₃ takes place above 600°C. BaTiO₃ powder was prepared by calcination of Ba(NO₃)₂ and TiO₂ precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO₃ confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (V_O^??).     

Microstructure and dielectric properties of ferroelectric barium strontium titanate ceramics prepared by hydrothermal method

Ba _x Sr_1-x TiO₃, nanoparticles with different Ba compositions were synthesized by a hydrothermal method. The mechanism of hydrothermal reactions was discussed based on DTA/TG, XRD and TEM characterizations. The result showed that perovskite structure was developed through the mutual diffusion between the intermediate phases and TiO₂ phase. The grain size of the Ba_0.77Sr_0.23TiO₃ (BST77) powders was about 20–40 nm. BST ceramics were made from the hydrothermal-derived BST powders and the dielectric properties of the BST ceramics were measured. Due to the small grain size and active surface energy of the BST powders prepared by hydrothermal method, the BST ceramics showed low sintering temperature. It was found that the BST77 ceramics sintered at 1280 °C showed dielectric constant peak dispersion which was believed to be caused by dimension domino effect.     

Preparation and characterization of high T c (1−x) BiScO3−xPbTiO3 ceramics from high energy ball milling process

(1-x)BiScO₃?xPbTiO₃ powders were synthesized from a mixture of the oxides Bi₂O₃, Sc₂O₃, PbO and TiO₂ using a Fritsch P4? vario-planetary ball milling systems. The pure perovskite structure of BS-PT powder can well be obtained and the crystallite size of the powders was greatly reduced to 18–25 nm after milling 4 h. The rhombohedral–tetragonal phase boundary was observed for the ceramics sintered at 1,000–1,100 °C when x was around 0.64 and 3–7 μm grain size was obtained, which is smaller than traditional method. High Curie temperature (T _c) and high dielectric constant can be obtained at the morphotropic phase boundary (MPB). As PbTiO₃ contents increased from 60 to 68 mol%, the Curie temperature T _c shifted toward higher temperature and the maximum dielectric constant increased. The experimental results demonstrate that the high-energy ball milling process is a promising method to prepare BS-PT materials.     

Synthesis, formation and characterization of lead indium niobate–lead titanate powders

In this study, powders of lead indium niobate–lead titanate (1???x)Pb(In_1/2Nb_1/2)O₃–(x)PbTiO₃ (PINT) binary system near the morphotropic phase boundary (MPB) composition with x?=?38 mol% PbTiO₃ are synthesized with the conventional mixed oxide and the wolframite methods via a rapid vibro-milling technique for the first time. The preparation method and calcination temperature have been found to show pronounced effects on the phase formation behavior of the PINT powders. The stabilized perovskite phase form of PINT can be synthesized by the wolframite method, while precursor phases are still found in powders prepared by the conventional method. Finally, this study shows that the rapid vibro-milling mixing technique is effective in preparing the phase pure perovskite of PINT powders.     

Structural Properties of Ga-Doped ZnO Nanoparticles Synthesized by Co-Precipitation Process

Ga-doped ZnO (GZO) nanoparticles were synthesized by co-precipitation process from starting precursors zinc dichloride (ZnCl₂) and Gallium (III) nitrate hydrate (GaN₃O₉). The deionized (DI) water was selected as the solvent. The as-precipitated powders were calcined at different temperature of 700 and 1000 °C for 2 h. For all samples, their crystal structures were investigated by X-ray diffraction (XRD) and surface morphologies were observed by a field emission scanning electron microscope (FE-SEM). The XRD results revealed that, the crystallinity of powders increases when the calcination temperature increases. Moreover, it is noticed that the intermixture phases of ZnO and Ga₂O₃ occur when the Ga doping content is exceeded the solubility limit of about 10%. In addition, SEM micrographs show the decrease of particle size with increasing Ga doping content due to lattice distortion that can hinder the crystal growth of ZnO.     

Enhancement in the physical properties of K0.5Na0.5NbO3 ceramics by the addition of 0.5 Li2O – 0.5K2O – 2B2O3 glass

The addition of powdered 0.5 Li₂O–0.5K₂O–2B₂O₃ (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K_0.5Na_0.5NbO₃ (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (?_r) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d₃₃) was found to be 130 pC/N for 1 wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of P_r with the increase in glass content, the P_r values were higher than that obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.     

Synthesis of fine Ca-doped BaTiO3 powders by solid-state reaction method—Part I: Mechanical activation of starting materials

Fine (Ba_0.98Ca_0.02)_1.002TiO₃ powders for high capacitance multilayer ceramic capacitors (MLCCs) application were synthesized by solid state reaction method. The effects of mechanochemical activation using high energy milling and the starting materials properties on the reaction temperature and on the final powder properties were investigated. Previous heavy milling of BaCO₃ and the adoption of fine, anatase-rich TiO₂ phase were effective in decreasing the reaction temperature and in increasing the tetragonality (=c/a). BaCaTiO₃ powders with a tetragonality of 1.0097, an average particle size of 213 ± 43 nm and a specific surface area of 6.30 m²/g were acquired after heat treatment at 985 °C for 2 h. MLCCs utilizing this developed powder showed superior dielectric and temperature characteristics to those with conventional, Ca-free BaTiO₃ powder.     

Electrodes for ferroelectric thin films

Abstract

Platinum and ruthenium oxide (RuO₂) deposited by ion beam sputter-deposition are evaluated for use as electrodes for PZT thin film capacitors. The effect of deposition temperature, film thickness, and the presence of oxygen on hillock formation in platinum is discussed. It is shown that the hillock density in Pt/Ti/SiO₂/Si films can be significantly reduced by properly controlling the processing conditions and film thickness. Stress measurements correlate with the experimental observation that depositing thinner platinum films (<800 Å) is an effective means of reducing hillock formation. The use of an intermediate deposition temperature 200–250°C also helps minimize hillock formation. Diffusion of the Ti adhesion layer into and/or through the platinum was significantly reduced by replacing the Ti with a TiO_x adhesion layer. RuO₂ electrodes are compared to Pt in terms of resistivity, surface morphology, microstructure and film orientation.     

Effect of attrition milling on the piezoelectric properties of Bi0.5Na0.5TiO3-based ceramics

Bismith sodium titanate (BNT)-based powders were prepared by conventionally mixed-oxide method using Bi₂O₃, Na₂CO₃ and TiO₂. The La₂O₃ was added as the modifier to the BNT composition for easily poling and reducing an abnormal dielectric loss at high temperatures. In this study, the investigated compositions were Bi_0.5Na_0.5TiO₃ and Bi_0.5Na_0.485La_0.005TiO₃. The powders were calcined at 900 °C for 2 h by slow heating rate at 100 °C/h. The calcined BNT-based powders were then attrition-milled for 3 h with a high speed at 350 rpm. After drying, the fine powders were uniaxially pressed and then cold-isostatically pressed (CIP) at 240 MPa for 10 min. All pressed pellets were sintered at 1000–1100 °C for 2 h in air atmosphere. The microstructure of sintered pellets was investigated by SEM. Results of dielectric and piezoelectric property measurement were also reported.     

Fabrication of Pyrochlore Phase Free PMN-PZT Ceramics via the Combustion Technique

A ferroelectric ceramic, 0.3Pb(Mg_1/3Nb_2/3)O₃-0.7Pb(Zr_0.48Ti_0.52)O₃ (PMN-PZT) with a pyrochlore-free phase was prepared by the combustion technique using glycine as fuel. The crystal structure, microstructure, dielectric and ferroelectric properties of the samples were investigated. It was found that the single peroveskite phase of PMN-PZT powders was obtained from the sample calcined at 850°C for 2 h. The purity phase was detected in all ceramic samples. The microstructures of the PMN-PZT powders exhibited an irregular shape and an agglomerated form and the average particle size increased with the increase of calcination temperature. The T_c trended to decrease while the average grain size increased when sintering temperature increased. At 1200°C, the ceramic exhibited maximum density (97%), highest dielectric constant (25000) and excellent ferroelectric properties (P_r = 24 μC/cm² and E_c = 4.5 kV/cm). The combustion technique is easier and can produce these ceramics more economically than other techniques.     

Synthesis of Pb(Zr, Ti)O3 Nanopowders by Milling Coprecipitation Method

Nano-size powders of lead zirconate titanate (PZT) were fabricated by a new milling coprecipitation method (MCP) improved from the conventional wet ball milling and precipitation. This method consists of slurry preparation from nanoparticles of TiO₂ with aqueous solution of ZrO(NO₃)₂ and Pb(NO₃)₂ with zirconia ball mill media, followed by precipitation with NH₄OH as precipitant. Milling media (1mm and 3mm balls) improves the precipitation homogeneity during processing. Single-phase perovskite structure of PZT was formed at a calcination temperature of 500C and powders of 50 nm particle size were obtained. Powders were characterized using TG-DTA, SEM and XRD methods. Sintering ability of powders and piezoelectric properties of the ceramics were also investigated.     

Investigation on FTIR spectra of barium calcium titanate ceramics

Barium titanate, which is applied in many fields, is a kind of very important ferroelectric material because it is lead free. Its physical properties are changed by replacement or addition of other ions. Here, barium calcium titanate ((Ba,Ca)TiO₃) ceramics are prepared. The concentration of calcium is up to 20 at.%. The Fourier transformation infrared spectroscopy (FTIR) measurement is carried out in order to reveal the vibration of crystal lattices. The influence of the replacement on the interaction between Ti and O can be observed by investigating the absorption peak of the Ti–O bond. The wavenumber of absorption peak of Ti–O bond becomes larger with increase of the content of Ca, even though the concentration of Ti is not changed. The wavenumber of absorption peak in (Ba_0.95Ca_0.05)TiO₃ is near 525 cm^?1 while that in (Ba_0.80Ca_0.20)TiO₃ is near 550 cm^–1. It is attributed to the decrease of the cell size. The length of Ti–O bond is shortened by replacement of Ca. Then the interaction between Ti and O is enhanced. The similar phenomenon is observed in (Ba,Mg)TiO₃ and alkali doped BaTiO₃ materials as well, supporting the mechanism. Furthermore, the aging effect in (Ba,Ca)TiO₃ and (Ba,Mg)TiO₃ systems is observed. The former exhibits a good stability when the latter shows unstable FTIR spectra. The influence of point defects on the aging effect is discussed. These results indicate that the FTIR measurement is helpful to study the relationship between the structure and physical properties of ferroelectric materials.     

Spherical shape Ba-based glass powders prepared by spray pyrolysis for MLCCs

Spherical shape BaO–B₂O₃–SiO₂ glass powders were directly prepared by high temperature spray pyrolysis at >1000 °C. The thermal and morphological characteristics of the prepared glass powders were investigated. The glass powders prepared at temperature of 1000 °C had spherical shape and hollow inner structure. On the other hand, the powders prepared at high temperature of 1300 °C had complete spherical shape and dense inner structure by complete melting. The mean size of the glass powders was 0.9 μm. The glass transition temperatures (T _g) of the glass powders obtained by spray pyrolysis at preparation temperatures between 1000 and 1300 °C were 601.1 °C regardless of the preparation temperatures. The specimen of the glass powders obtained by spray pyrolysis at the preparation temperature of 1300 °C had small number of voids even at low sintering temperature of 700 °C. In addition, the specimen sintered at temperature of 800 °C had dense microstructure without voids.     

Dielectric properties of zinc titanate thin films prepared by Rf magnetron sputtering

Zinc titanate thin films of ~500 nm in thickness were synthesized by an RF magnetron sputtering using a sintered ceramic target. After annealing in temperature ranges of 300–800 °C, their phase transition and dielectric properties were investigated as a function of annealing temperature. Crystalline ZnTiO₃ phase was first detected at the annealing temperature of 500 °C within XRD detection limit though the sputtered film was mainly amorphous. ZnTiO₃ still remained as a main phase although the slight decomposition of ZnTiO₃ into Zn₂TiO₄ and TiO₂ occurred in association with the increase of annealing temperature. Dielectric properties were apparently improved with increase of annealing temperature and showed maximum value at 650 °C. Further higher temperature annealing caused inferior dielectric property. These results were explained in terms of the presence of TiO₂ (rutile) phase, resulting from the decomposition of ZnTiO₃ phase, and the morphology of the thin film.     

Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders

Studies on the Preparation and microwave properties of Mg doped barium strontium titanate (BSTO) ceramics sintered from Sol–Gel-derived powders. The crystal structure and microstructure of Ba_0.60Sr_0.40TiO₃ ceramics doped with Mg has been investigated. The microwave complex permittivity of BST ceramics doped with Mg powders is investigated in 100 MHz–6 GHz ranges by coaxial-transmission technique and the calculation of the equivalent medium theory. Experimental results showed that the typical cubic phase structure and the diffraction peaks of secondary phase that MgO phase become stronger with increasing Mg²⁺ content in the XRD pattern of the Mg doped BST ceramic sintered at 1250°C. The real part of the microwave complex permittivity of BSTM30 ceramic powders is excellent described by results of calculation of Bruggeman theory in wide powder content.     

The fabrication,characterization of honeycomb-type porous Ag/N-TiO2 nanomaterial and its application in SERS study

ABSTRACT

Combined template method with sol-gel method to make the mixed solution including polystyrene microsphere emulsion, TiO₂ sol and NH₃·H₂O aging at room temperature. Annealing at 500 centigrade for 2 hours on mesoporous TiO₂ nano material doped with nitrogen. Wrapped Ag nanoparticles on the surface of mesoporous TiO₂ nano material through redox reaction. The morphology and optical porosities were characterized by Scanning electron microscope (SEM), X-ray diffraction (XRD), BET tester and Surface enhanced Raman scattering (SERS). The results showed this material has excellent surface enhanced Raman effect, optical absorption effect and also has a great specific surface area.     

Facile one-pot synthesis of uniform niobium-doped titanium dioxide microparticles for nanostructured dye-sensitized solar cells

In this study, we present the deposition of uniform sponge-like films using a novel niobium-stabilised TiO₂ gel for dye-sensitized solar cells (DSCs) applications. The introduction of Nb into TiO₂ lattice limits the transformation from anatase to rutile phase, stabilising anatase nanoparticles. The films are composed of uniform spherical particles with diameter around 3 μm, containing small nanoparticles with the average grain size of 40 nm, deposited by dip coating method. X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) reveal that Nb⁵⁺ is well incorporated into the titania crystal lattice without forming specific niobium phases. UV–Visible spectra show that the doped-TiO₂ films have lower band gap energy than that of undoped-TiO₂, extending the absorption of TiO₂ into visible region. Diffuse reflectance spectroscopy (DRS) shows that the presence of rutile nanoparticles in photoanodes may improve the photovoltaic performance of solar cells due to better light scattering ability of rutile than anatase phase. The DSC stabilised with 3 at. % Nb (i.e., PN3) had the highest power conversion efficiency of 7.38 % as a result of less recombination, which is demonstrated by electrochemical impedance spectroscopy (EIS).     

The Rutile Phase of TiO2/Graphene Films: Sol–Gel Method,Phase Transition,Photocatalytic Properties

Abstract

TiO₂ materials are of great interest in different applications because of the controllable preparation of different structures. In this paper, the TiO₂ and TiO₂/graphene films with different phase structure and inserted graphene layer between Cu substrate and TiO₂ film were prepared by sol–gel method at different annealing temperatures, and then used as catalysts for photo-degradation of methylene blue (MB) dye solution under ultraviolet irradiation using 15?W of ultraviolet lamp. The effects of annealing temperature and graphene layer on the phase structure, morphology, chemical composition, binding energy level, and photocatalytic performance of TiO₂ films were studied in details. XRD results reveal that the anatase phase of TiO₂ films transfers to rutile phase with the increase in annealing temperature, and the introducing of graphene film layer can accelerate the phase transformation of anatase to rutile and improve the crystallization quality of TiO₂ films. It is found that the MB degradation efficiency of TiO₂ and TiO₂/graphene films is enhanced with the increasing annealed temperature, which shows that the existence of rutile phase, well crystalline quality and the better dispersion of the TiO₂ particles are helpful in photocatalytic behavior. In addition, compared to the rutile phase TiO₂ film, the rutile phase TiO₂/graphene films at annealed temperatures of 900?°C exhibit much higher photocatalytic activity due to the introduction of graphene films.