Room temperature synthesis of spherical mesoporous titania

This work reports a facile hydrolysis method for the synthesis of spherical mesoporous titania particles using titanium tetrachloride under mild conditions. The method can be easily controlled or expanded. The influences of various reaction conditions including concentration of Ti⁴⁺ ions and water content on the formation of mesoporous titania particles were systematically investigated. The titania particles were characterized by X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM) and Brunauer-Emmett-Teller (BET) surface areas. Experimental results showed that the mesoporous titania particles have special surface structure and excellent thermally stable mesoporous structure after annealing at high temperatures (500 °C). The effects of various reaction conditions, such as concentration of Ti⁴⁺, H₂O/n-butanol volume ratio and reaction temperature, on formation, crystal phase, morphology of titania particles were investigated.     

Structural evolution,dielectric and energy storage properties of Na(Nb1−xTax)O3 ceramics prepared by spark plasma sintering

Phase pure NaNb_1−xTaxO₃ ceramics have been successfully prepared by spark plasma sintering (SPS) process at 950–1150 °C. The structural evolution, dielectric and energy storage properties as a function of Ta-doping level were studied by X-ray diffraction (XRD) Rietveld refinement, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), Raman spectroscopy, scan electron microscopy (SEM) and ferroelectric analyzer. It was found that small level of Ta-doping induced the stabilization of ferroelectric phase from antiferroelectric NaNbO₃, while high level of doping induced further transition from ferroelectric to paraelectric phase. The doping of Ta led to the decrease in Tc and dielectric loss. The NTN4 and NTN6 composition exhibited enhanced dielectric response due to the coexistence of ferroelectric/antiferroelectric or paraelectric phases. The presence of oxygen vacancies in the sintered body were confirmed, which gave rise to the loss at high temperature. The doping of Ta decreased the concentration of oxygen vacancies. Maximum energy density of ∼0.9 J/cm³ could be obtained for x = 0.6 composition with the BDS of ∼160 kV/cm and efficiency of ∼87%.     

Polydimethylsiloxane–PbZr0.52Ti0.48O3 nanocomposites with high permittivity: Effect of poling and temperature on dielectric properties

Polydimethylsiloxane (PDMS)/lead zirconate titanate (PbZr_0.52Ti_0.48O₃, PZT)-based nanocomposites with high dielectric constant (permittivity, k) are prepared through room temperature mixing. The effect of PZT loading on electrical and mechanical properties of the PDMS–PZT composites is extensively studied. It is found that there is significant increase in permittivity with PZT loading and decrease in volume resistivity. All the composites have low dielectric loss compared to permittivity value. It is observed that there is increase in permittivity and decrease in volume resistivity of composites after poling, which is due to the dipolar polarization. It is found that both permittivity (ε′) and alternating current conductivity (σ_ac) are increased with temperature at low frequency (1 Hz) and decreased with temperature at high frequency (1 MHz). The above composites are sensitive to external pressure and can be used as pressure/force sensor. The tensile strength and % elongation at break decreases with PZT loading, which is due to the nonreinforcing behavior of PZT ceramic. PZT particles distribution and dispersion in PDMS matrix are observed through field emission scanning electron microscopy, high resolution transmission electron microscopy, and atomic force microscopy/scanning probe microscopy. Thermal stability of composites increased with the PZT loading which is due to higher thermal stability of PZT particles compared to PDMS matrix. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47307.     

Higher permittivity of Ni-doped lead zirconate titanate,Pb[(Zr0.52Ti0.48)(1-x) Nix]O3, ceramics

The paper reports highest obtained dielectric constant for Ni-doped Lead Zirconate Titanate [PZT, Pb(Zr_0.52Ti_0.48)O₃] ceramics. The Ni-doped PZT ceramic pellets were prepared via conventional solid-state reaction method with Ni content chosen in the range 0–20?at%. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were employed to investigate the crystal structure of the prepared ceramics. The X-ray diffraction analysis indicated that the ceramic pellets had crystallized into tetragonal perovskite structure. A minute displacement of XRD peaks was detected in the diffraction spectra of Ni-doped PZT ceramic samples which when examined by size-strain plot (SSP) method revealed presence of homogenous strain that decreased with increase in concentration of Ni. In FTIR the maximum absorption at 597?cm^?1, 608?cm^?1, 611?cm^?1, 605 and 613?cm^?1 for Ni?=?0, 5, 10, 15 and 20?at%, respectively, confirmed the formation of perovskite structure in all the compositions and the slight shift suggests decrease in cell size on doping. The values of dielectric constant (ε′) & tanδ as a function of frequency and temperature were measured for the prepared ceramics and it revealed highest ever reported dielectric constant for Ni - doped PZT with Ni?=?5?at%. The dielectric variation with temperature exhibited a diffused type ferroelectric–paraelectric phase transition for the doped samples. Also, the maximum dielectric constant value (ε′_max) decreased while the phase transition temperature increased with increase in doping concentration of Ni. The estimated activation energy of different compositions was found to increase from 0.057 to 0.068?eV for x?=?0.00 to x?=?0.20 in ferroelectric phase. The piezoelectric, ferroelectric and magnetic properties were also investigated.     

Preparation of corundum structure Sn-doped In2O3 nanoparticles via controlled co-precipitating and postannealing route

Corundum structure Sn-doped In₂O₃ nanoparticles were first synthesized by a controlled co-precipitating and postannealing method. X-ray powder diffraction (XRD), electron diffraction (ED), transmission electron microscopy (TEM), and X-ray photoelectron spectrometer (XPS) were used to characterize the products, indicating that the products were well-crystallized Sn-doped In₂O₃ nanoparticles with corundum structure. The particles were spherical in shape with sizes in the range of 10–20 nm.     

The phase and morphological evolution of Ti3SiC2 MAX phase powder after HF treatment

The aim of this study is to investigate the phase and morphological evolution of the prepared Ti₃SiC₂ MAX phase powder after immersion in hydrofluoric acid (HF) solution for 24, 72, 96 and 120?h. The phase and morphological evolution of Ti₃SiC₂ was analyzed using X-ray diffraction (XRD) patterns, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). XRD results revealed that after 24?h HF treatment the diffraction peaks of Ti₃SiC₂ were fully disappeared and this treatment led to the decomposition of Ti₃SiC₂ to TiC. XRD and EDS findings demonstrated that de-intercalation of Si layer occurred after HF treatment. Moreover, SEM images showed that the morphological shape of TiC particles significantly changed as a function of HF treatment times. In summary, the shape of TiC particles changed from the polyhedron to hexagonal, then to truncated octahedron, octahedron and cubic.     

The structural and electrical comparison of Y2O3 and Ti-doped Y2O3 dielectrics

A Ti-doped Y₂O₃(Y₂Ti₂O₅) dielectric on polycrystalline silicon followed by rapid thermal annealing results in improved characteristics including a higher effective dielectric constant, higher breakdown electric field, lower electron trapping rate, and larger charge-to-breakdown when compared with Y₂O₃. The performance of high-k Y₂O₃ and Y₂Ti₂O₅ dielectrics were investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), capacitance-voltage, and current density-voltage. Incorporating Ti into the Y₂O₃ dielectric imparts improvements in the structural and electrical performance of the material. The Y₂Ti₂O₅ dielectric with 800 °C annealing treatment has the best performance among all the samples tested.     

Synthesis and characterisation of La(Co1/2Ti1/2)O3

Single phase, dense La(Co_1/2Ti_1/2)O₃ (LCT) ceramics have been fabricated using conventional solid state synthesis. Samples were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), Raman spectroscopy and their dielectric properties were studied at radio and microwave frequencies. X-ray and electron diffraction conclusively revealed that LCT contained in-phase and antiphase rotations of the O-octahedra, consistent with and a⁻a⁻c⁺ tilt system in the Glazer classification. However, XRD indicated that the Co and Ti ions were disordered on the B-site whereas TEM and Raman spectroscopy exhibited reflections and modes which suggested that partial ordering may be present. Moreover, some Raman bands could only be explained by assuming that at least some of the octahedra exhibited a Jahn–Teller distortion. Dielectric measurements indicated that LCT is insulating with low dielectric loss, 0.0024 at 1 MHz and frequency independent relative permittivity, ε_r=25. A quality factor, Q×f_o=38,000 was obtained at microwave frequencies along with a temperature coefficient of the resonant frequency, TCF=−42 MK⁻¹.     

Synthesis of AuPd alloyed nanoparticles via room-temperature electron reduction with argon glow discharge as electron source

Argon glow discharge has been employed as a cheap, environmentally friendly, and convenient electron source for simultaneous reduction of HAuCl₄ and PdCl₂ on the anodic aluminum oxide (AAO) substrate. The thermal imaging confirms that the synthesis is operated at room temperature. The reduction is conducted with a short time (30 min) under the pressure of approximately 100 Pa. This room-temperature electron reduction operates in a dry way and requires neither hydrogen nor extra heating nor chemical reducing agent. The analyses using X-ray photoelectron spectroscopy (XPS) confirm all the metallic ions have been reduced. The characterization with X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) shows that AuPd alloyed nanoparticles are formed. There also exist some highly dispersed Au and Pd monometallic particles that cannot be detected by XRD and transmission electron microscopy (TEM) because of their small particle sizes. The observed AuPd alloyed nanoparticles are spherical with an average size of 14 nm. No core-shell structure can be observed. The room-temperature electron reduction can be operated in a larger scale. It is an easy way for the synthesis of AuPd alloyed nanoparticles.     

Structural and electrical studies of excessively Sm2O3 substituted soft PZT nanoceramics

The solid solution of Pb_1-x Sm_2x/3 (Zr_0.6 Ti_0.4) O₃ ceramics with x = 0.1, 0.2, 0.3, and 0.4 was prepared via the high-energy ball milling technique. Further, the effect of excessive Sm₂O₃ substitution at Pb-site on structural, dielectric, and dc-conductivity properties was studied. The X-ray diffraction (XRD) analysis confirmed that all samples were crystallized with perovskite and pyrochlore diphase form. Excess Sm³⁺ substitution in the PZT system increases the pyrochlore volume fraction from 5 to 20% and induces a structural phase transition from rhombohedral to a tetragonal structure. The microstructural study by TEM and SEM indicated that the particles were spherical with an average size of 43–55 nm. The frequency and temperature-dependent dielectric constant for all compositions was carried out and it is obtained that the dielectric constant decreases with Sm³⁺ content. The phase transition temperature first decreases up to x = 0.2 and then increases for the higher concentration of samarium. The dc-conductivity studies revealed that all samples showed an unusual mixed TCR effect (both positive and negative temperature coefficient of resistance). Such properties of the studied samples indicate that the material is suitable for potential applications in thermistors, and temperature sensors of the automotive, and petroleum industries.     

Combining effects of TiO6 octahedron rotations and random electric fields on structural and properties in Na0.5Bi0.5TiO3

The structural and dielectric properties of Na_0.5Bi_0.5TiO₃ (NBT) ceramics and crystals have been investigated and are compared to that of Pb(Zr_0.55Ti_0.45)O₃ (PZT55/45) and Pb(Mg_1/3Nb_2/3)_0.72Ti_0.28O₃ (PMNT 72/28) ceramics. X-ray diffraction (XRD) profiles for (100), (110), (111), (200), (220), and (222) (referred to cubic structure) reveal that the monoclinic structure with Cc space group exists both in the NBT single crystal and ceramics. The diffraction profile obtained with high resolution laboratory XRD for the NBT single crystal can be well described, using Cc model instead of R3c model. The dielectric constant of NBT below T_hump shows some similarity to that of PZT45/55 ceramics below 50°C in which oxygen octahedron rotations cause the frequency dispersion of the dielectric constant. The temperature-dependent dielectric constant for NBT can be deconvolved into two independent processes. The lower temperature process shows a typical relaxor characteristic and follows the Vogel-Fulcher relationship. The other process at higher temperature shows less frequency-dependent behavior. Comparing the dielectric constant of NBT with that of PZT55/45 and PMNT72/28 reveals that both oxygen octahedral rotations and random electric fields play an important role in the frequency dispersion of the dielectric constant for NBT relaxor feroelectric.     

Preparation and characterization of orthoferrite PrFeO3 nanoceramic

In the present study, orthoferrite PrFeO₃ (PFO) ceramic was reported to be synthesized by high energy ball milling and subsequent sintering. Thermal, dielectric, and optical properties of the synthesized samples were investigated. The PrFeO₃ ceramic samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetry (TG), differential thermal analysis (DTA), X-ray photoemission spectroscopy (XPS), and ultraviolet–visible spectroscopy (UV–vis). Based on the XPS analysis, PFO belongs in the rank of ceramics with a good colossal dielectric constant (CDC) behavior, as also confirmed by the measured dielectric properties. Results also showed that an increase in the frequency values leads to an increase in the electron hopping frequency and subsequently an increase in the charge carrier mobility, which is also the case with ac conductivity. The UV–vis absorption spectra of the PFO samples sintered at 1400 °C also showed that maximum absorption takes place in higher frequency as well as in higher energy ranges.     

Voltage effect of corona poling on characteristics of PbZrxTi1−xO3 (PZT) film

The paper investigates the voltage effect of corona poling on the characteristics of PbZr_xTi_1−xO₃ (PZT) thin film. Purchased PZT powder and lab-made PZT solution were mixed together as sol-gel that was spin-coated on titanium (Ti) substrate. X-ray diffractometer (XRD), scanning electron microscopy (SEM), impedance analyzer were utilized to measure the orientation and dielectric characteristics of films for comparison. The experimental results indicated that the poling voltage would not affect the orientation of crystallization, microstructure and grain size of PZT film surface. However, the higher applied poling voltage would result in better charge storage capacity and energy transfer efficiency of the film.     

Preparation,characterization and the antimicrobial properties of metal ion-doped TiO2 nano-powders

TiO₂ samples doped with lithium, sodium, magnesium, iron or cobalt were prepared by high-energy ball milling for different periods of time. The crystalline phase, chemical composition, crystalline size and photo-absorption were characterized by X-ray diffraction spectroscopy (XRD), X-ray photoelectron spectroscopy (XPS) and Ultraviolet visible diffuse reflectance spectroscopy (UV - Vis - DRS), Fourier transform infrared spectroscopy (FT - IR) and scanning electron microscopy (SEM). The antimicrobial properties of the modified TiO₂ samples were evaluated with E. coli and S.aureus assays. The results of the XRD show that the TiOSO₄, Ti₃O₅, Li₂TiO₃ and NaTi₂O₄ phases appear along with Li, Na and Mg doped TiO₂. However, XPS spectra indicated that Ti exists as both Ti³⁺ and Ti⁴⁺ in Na-doped TiO₂ samples. Ti³⁺, due to its narrow band gap, is highly active in promoting visible light-induced photocatalytic activity. SEM images showed that the crystalline size of TiO₂ is reduced and has a common-round and hexagonal plate morphology after milling. The modified TiO₂ samples had the best antimicrobial activities after 3 h of milling. In particular, the antimicrobial rate of TiO₂ 5% doped with transition metals (Co, Fe) reached 100% against E. coli, but the antibacterial rate against S. aureus for Co and Fe dopants was 98.4% and 98.2%, respectively.     

A new sensor based on amino-functionalized zirconium metal-organic framework for detection of Cu2 + in aqueous solution

Amino(-NH₂) functionalized zirconium metal-organic framework UiO-66 were synthesized in household microwave oven. The structural properties and morphology of the obtained UiO-66-NH₂ nanoparticles were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS). UiO-66-NH₂ sensor show high selectivity and sensitivity toward Cu^2 + over other tested metal ions. In addition, the possible sensing mechanism is also discussed.     

Influence of silver on the structure,dielectric and antibacterial effect of silver doped bioglass-ceramic nanoparticles

We present the structural, dielectric, biocompatibility and antibacterial properties of nano-sized calcium phosphosilicate bioglass ceramics doped with 0, 2, 4 and 6 mol% Ag₂O. Sol-gel processes were chosen to synthesize the silver embedded nanosized glass ceramic particles. All samples were characterized by powder X-ray diffraction (XRD), thermogravimetric analysis, Fourier transform infrared (FTIR) spectroscopy, UV–visible and high resolution transmission electron microscopy (HR-TEM). The glass-ceramic nature of the samples is confirmed by XRD analysis. The FTIR spectra reveal the probable stretching and bending vibration modes of silicate and phosphate groups. UV–visible absorption spectra reveal the silver embedment as Ag⁺/Ag° form in the glass matrix. Nano-size of the glass ceramics and silver nanoparticle embedment in glass matrix are confirmed by HR-TEM analysis. Dielectric spectra of samples reveal non-Debye relaxation processes. The dielectric constant of samples initially decreased and then increased with Ag₂O content. The antibacterial activities of these bioceramics were tested with different bacteria using an agar well diffusion method. Silver doped samples show good antibacterial effects without compromising the formation of hydroxyapatites. The dielectric constant of the bioglass ceramics is correlated to their antibacterial performance, with low dielectric constants giving higher antibacterial activity.     

Structure,electrochemical impedance and Raman spectroscopy of lithium-niobium-titanium-oxide ceramics for LTCC technology

Resultsof Electrochemical Impedance Spectroscopy (EIS) are reported for lithium-niobium-titanium-oxide (LNTO) ceramics synthesized by a solid-state reaction method with two functional additives (MoO₃ or ZnO) in the temperature range 323 K - 573 K and frequencies between 10^?1 Hz and 10⁷ Hz. Scanning electron microscopy (SEM) reveals a textured morphology of rod and plate-like particles that are typical for M-phase LNTO materials, while X-ray diffraction (XRD) analysis confirms the formation of an M-phase member compound with an approximate structure of Li₇Nb₃Ti₅O₂₁. Complex impedance analysis indicates that its overall electrical resistivity behavior depends mostly on the grain boundary processes. EIS analysis shows a negative temperature coefficient of resistance behavior (NTCR) in a defined temperature range in two LNTOs and thermal activation of the conduction mechanisms. The low dielectric constants of 5.5 and 12.1 at 1 MHz were found for the first and second LNTOs, respectively. Complimentary Raman spectroscopic measurements, despite very large crystallographic unit cell of LNTO, reveal only a small number of lines, which is the consequence of a “molecular” nature of materials.     

A novel way to production yttrium glass microspheres for medical applications

In this paper a novel method of producing yttrium aluminum silicate microspheres is reported. Yttrium aluminum silicate microspheres around 20–50 μm in size were obtained when an aqueous solution of Y(NO₃)₃ and Al(NO₃)₃ was added to tetraethyl orthosilicate (TEOS) and pumped into stirred silicone oil. The particles produced by this method are regularly shaped and very close to spherical. The amorphous structure, Y-O-Si bonds, spherical shapes, composition, and element distribution were investigated by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), X-ray fluorescence spectroscopy (XRF), carbon/sulfur analysis, and SEM/EDS mapping analysis. The results obtained demonstrate that the silicone oil spheroidization method is suitable for the production of yttrium aluminum silicate microspheres. This study also reveals that a high temperature is not required for the production of yttrium aluminum silicate microspheres.     

Photocatalytic oxidation of cyclohexane over TiO2 nanoparticles by molecular oxygen under mild conditions

The structure, physical characteristics and photocatalytic selective oxidation properties of nanometer‐size TiO₂ particles produced by a sol–gel method were studied by X‐ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), X‐ray photoelectron spectroscopy (XPS), electron paramagnetic resonance (EPR) and photocatalytic selective oxidation measurements. Analysis of the XRD results shows that sol–gel‐produced TiO₂ nanoparticles have the anatase structure at annealing temperatures ≤973 K, that the rutile structure begins to emerge at annealing temperatures ≥973 K and the particles have the pure rutile structure at 1023 K. DRS indicates that the obtained TiO₂ nanoparticles exhibit a blue shift with decreasing crystallite size. Analysis of the XPS results shows that the TiO₂ nanoparticles have a lot of oxygen vacancies. The EPR spectrum of TiO₂ at 77 K is composed of a strong isotropic EPR Surface‐Ti³⁺ signal(I) at g = 1.926 and a weak broad Bulk‐Ti³⁺ signal (II) at g = 1.987. Quantitative EPR indicates that both signals show a size and temperature dependence. Photocatalytic oxidation of cyclohexane into cyclohexanol with high selectivity and activity has been obtained by activation of molecular oxygen over sol–gel‐produced TiO₂ nanoparticles under mild conditions in dry solvent, which reveals that the quantum size effect and surface state effect of nanoparticles are key points for governing the selective photocatalytic reaction. The photocatalytic oxidation mechanism under dry solvent is different from that in aqueous solutions. Copyright © 2003 Society of Chemical Industry     

Surface doping of TiO2 powders via a gas–melt reaction using thermal plasma as an excitation source

Surface doping is an effective method to engineer and functionalize powder materials without modulating the internal crystal structure. This study proposed a facile technique for surface doping via a gas–melt reaction using thermal plasma as an excitation source. Doping molten titania (TiO₂) particles with La was preliminarily explored owing to the broad photocatalytic applications of TiO₂. Scanning electron microscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy, transmission electron microscope, diffuse reflectance spectroscopy, photoluminescence spectroscopy and Fourier transform infrared spectroscopy were adopted to characterize the morphology, phase composite, chemical state, fine structure, and optical property of the doped TiO₂ powder, respectively. Results indicated that molten TiO₂ doped with La solidified into spherical particles under the effect of surface tension. No modification of the internal crystal structure was indicated in the XRD patterns, except that the diffraction peak of rutile TiO₂ (110) shifted to low angles after surface doping with La. The obtained TiO₂ powder exhibited sensitivity to sunlight and near-infrared light, and a La/Ti atomic ratio of 19.4% was achieved. The diffusivity D_i of La in molten TiO₂ ranged from 10⁻⁸ m²/s to 10⁻⁷ m²/s, as determined from the gas–melt reaction.