Preparation of Gadolina Stabilized Bismuth Oxide Doped with Boron via Electrospinning Technique

In this study, boron doped and undoped poly (vinyl) alcohol/bismuth–gadolina acetate (PVA/Bi–Gd) nanofibers were prepared using electrospinning technique then calcinated at 800 °C for 2 h. The originality of this study is the addition of boron to metal acetates. The effects of boron doping were investigated in terms of solution properties, morphological changes and thermal characteristics. The characteristics of the fibers were investigated with FT-IR, XRD, SEM and BET. The addition of boron did not only increase the thermal stability of the fibers, but also their diameters, which yielded stronger fibers. XRD analyses showed that boron doping increased the peak intensities and indicated that the boron doping enhanced the crystallite size. Moreover, no shifts were noticed in diffraction angles for boron doped and undoped samples. Therefore, boron doping did not significantly alter the lattice spacing. The SEM micrograph of the fibers showed that the addition of boron resulted in the formation of cross-linked bright-surfaced fibers. The average fiber diameter for boron doped and undoped fiber mats were 204 and 123 nm, respectively. Also, grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 140 and 118 nm, respectively. The BET results showed that boron undoped and doped Bi₂O₃–La₂O₃ nanocrystalline powder ceramic structures sintered at 800 °C have surface areas of 59.72 and 39.80 m²/g, respectively.     

Synthesis and Properties of Boron Doped NaxCo2O4 Nanocrystalline Ceramics

Sodium cobalt oxide (NaCo₂O₄) nanofibers with diameters ranging between 20 and 200?nm were prepared by electrospinning a precursor mixture of PVA/(Na–Co) acetate. This was the first time any such attempt was made. Afterwards, the electrospun nanofibers were subjected to calcination treatment. The characteristics of the fibers were investigated using a Fourier transform infrared spectroscopy, a X-ray diffractometer, and a scanning electron microscopy. The boron doped and undoped NaCo₂O₄ nanofibers calcined at 850?°C were polycrystalline of the γ Na_xCo₂O₄ phase having diameters ranging between 20 and 60?nm with grain sizes of 5–10?nm, and the nanofibers calcined at 800?°C were single crystals having linked particles or crystallites with particle sizes ranging between 60 and 200?nm. The results indicated a significant effect of calcination temperature on the crystalline phase and morphology of the nanofibers. It could be seen in the SEM micrograph of the fibers that when boron was added, this resulted in the formation of cross-linked bright-surfaced fibers. The average fiber diameter for boron doped and undoped fiber mats were 204 and 123?nm, respectively. The grain diameters of boron doped and undoped nanocrystalline sintered powders were measured as 140 and 118?nm, respectively.     

Calcia Stabilized Ceria Doped Zirconia Nanocrystalline Ceramic

Calcia-stabilized cerium doped cubic zirconia nanocrystalline ceramic was synthesized using poly (vinyl alcohol) as a polymeric precursor. Obtained ceramic was pressed into a cylindrical pellet and sintered at 850 °C. The calcined and sintered ceramics were characterized by XRF, XRD, BET and SEM. The XRD pattern of the calcined ceramic shows that the ceramic has a face centered cubic crystal structure. The SEM results show that the grain size of the ceramic was increased after sintering. The BET surface areas were determined as 13.236 and 4.397 m² g^?1 for the calcined and sintered ceramics, respectively.     

Fabrication and characterization of boron doped yttria‐stabilized zirconia nanofibers

Boron doped and undoped poly(vinyl) alcohol/zirconium‐yttrium acetate (PVA/Zr‐Y) nanofibers were prepared by electrospinning using PVA as a precursor. The effect of boron doping was investigated in terms of solution properties, morphological changes and thermal properties. The effect of boron doping on calcined yttria stabilized zirconia (YSZ) fibers was evaluated by X‐ray diffraction (XRD) and X‐ray photoelectron spectroscopy analysis. XRD analysis revealed varying amounts of monoclinic and tetragonal zirconia present in the undoped fibers calcined at 800°C. The average crystallite sizes of the undoped YSZ were increased from 9.28 to 22.79 nm with calcining temperature increasing from 250 to 800°C. The crystallite size was enhanced with boron doping. The systematic evolution of morphological features in the spun and the processed fibers were employed by scanning electron microscopy. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Synthesis,structural characterization,and photoluminescence properties of TTB‐type PbTa2O6:Eu3+ phosphor

Undoped and Eu³⁺‐doped tetragonal tungsten bronze (TTB) PbTa₂O₆ phosphors were synthesized by using solid‐state reaction method. Synthesized samples were characterized by XRD, SEM‐EDS, and photoluminescence analyses. XRD results revealed TTB‐type crystal structure with single phase up to 10 mol% Eu³⁺ doping concentration. In SEM‐EDS analyses, elemental composition of Pb decreased with the increasing concentration of Eu³⁺. Emissions at the excitation wavelength of 398.5 nm were observed at 593.2 and 618.8 nm due to ⁵D₀→⁷F₁ transitions and ⁵D₀→⁷F₂ transitions, respectively. Emission increased with the increasing Eu³⁺ doping concentration up to 10 mol% and not observed concentration quenching.     

Photoluminescence characterization and heat treatment effect on luminescence behavior of BaTa2O6:Dy3+ phosphor

Undoped and Dy³⁺‐doped barium tantalate phosphors were synthesized by the solid‐state reaction method at 1425°C. Also, 10 mol% Dy³⁺‐doped BaTa₂O₆ was sintered between 1150 and 1425°C in order to determine temperature effect on structural and luminescence properties. Afterwards, they were characterized by XRD, SEM‐EDS and photoluminescence (PL) analyses. PL spectra exhibited the excitation peaks between 300 and 440 nm. Two typical emissions were observed at 486.2 nm (blue) and 577.7 nm (yellow) due to the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions, respectively. Emission intensities increased with increasing doping concentration of Dy³⁺ up to 10 mol% and then decreased due to the concentration quenching effect. Moreover, depending on the increase in heat treatment temperature, the intensity of emission reached maximum at 1425°C. The calculated CIE chromaticity coordinates of phosphors located in the white light region.     

Synthesis of Cerium‐Doped Gd3(Al,Ga)5O12 Powder for Ceramic Scintillators with Ultrasonic‐Assisted Chemical Coprecipitation Method

Cerium‐doped Gd₃(Al,Ga)₅O₁₂ powders have been synthesized with ultrasonic‐assisted chemical coprecipitation method (UACC), and the traditional chemical coprecipitation method (CC) was also employed for comparison. The structure and morphology of powders were investigated by XRD, BET, and TEM. The powders were used for preparing ceramics at different temperatures. The specific surface areas of UACC and CC powders calcined at 800°C were 66 and 29 m²/g, respectively. Ceramics derived from UACC and CC powders were sintered at 1600°C, and the densities are 6.67 and 6.48 g/cm³, respectively. UACC is an attractive method for synthesizing GAGG powder for preparing ceramic scintillators.     

Synthesis of nano-sized indium oxide (In2O3) powder by a polymer solution route

Indium oxide (In₂O₃) is a n-type semiconductor with various applications in thin film coatings, on the basis of its optical properties, and in gas sensing equipment, due to its high sensitivity to various oxides such as CO_x and NO_x. In this study, a synthesis process for obtaining In₂O₃ nanoparticles is examined. The precursor used is indium nitrate hydrate (InN₃O₉·H₂O) because of its high solubility in water. By dissolving the nitrate salt in a PVA (polyvinyl alcohol) solution, the precursor is dispersed homogeneously, which reduces the agglomeration of the resulting powder. Calcination at a low temperature of 200–250 °C burns out the organic materials of the PVA with NO_x gas emission and allows the oxidation of the indium, resulting in indium oxide nanoparticles. The influence of the PVA solution characteristics and the heat treatment temperature on the powder morphology and size was analyzed by using SEM, TEM, XRD, TGA/DSC, and four point BET for a specific surface area analysis. The measured specific surface area varies from 3 m²/g to 76 m²/g depending on the calcination temperature, and the particle size of the synthesized powders is under 10 nm for the samples heat treated at 300 °C.     

Synthesis of ultra-fine α-Al2O3 fibers via electrospinning method

Ultra-fine Al₂O₃ fibers were synthesized via electrospinning technique using PVP/ethanol polymer solution and aluminium acetate sol followed by calcinations at higher temperature. The formation, crystalline phase, surface morphology, fibers diameter and surface area of alumina ultra-fine fibers were characterized using FT-IR, TGA/DTA, XRD, SEM, TEM and BET analytical techniques. The results show that pure and crystalline α-Al₂O₃ ultra-fine fibers were formed with fiber diameter in the range of 100–500 nm and BET surface area of the fibers were found to be 40 m²/g.     

Li2ZrO3 based Li-ion conductors doped with halide ions & sintered in oxygen-deficient atmosphere

All-solid-state batteries have recently attracted much attention for their high energy density and safety. Li₂ZrO₃-based Li-ion conductors with high electrochemical stability have potential applications for electrolytes in all-solid-state batteries. In this work, comparative investigations of Li₂ZrO₃ and halogen doped Li₂ZrO₃ ceramics were conducted by sintering at 700 °C in air or in oxygen-deficient atmosphere which was induced by a simple setup covering with corundum crucible. The analysis of phase composition reveals that the undoped Li₂ZrO₃ ceramic sintered in air contains pure monoclinic phase, while halogen-doped Li₂ZrO₃ sintered in air and all ceramics sintered in oxygen-deficient atmosphere are simultaneously composed of monoclinic and tetragonal phases. Li₂ZrO₃ ceramic with tetragonal phases has higher conductivity (0.28 mS cm⁻¹ for undoped Li₂ZrO₃) than the pure monoclinic Li₂ZrO₃ (0.07 mS cm⁻¹), and halogen doping can further enhance the conductivity of Li₂ZrO₃ ceramics higher than 0.5 mS cm⁻¹ at room temperature.     

Two-step sintering of Sm2O3 doped ceria stabilized zirconia

Effect of Sm₂O₃ addition and two-step sintering of Ceria Stabilized Zirconia (CSZ) on microstructure and mechanical properties were investigated in the present work. Samaria doped CSZ (SmCSZ) nanopowders were prepared by co-precipitation synthesis from their respective nitrate salts. Synthesized powders were calcined at 1000?°C for 2?h and then compacted to ?10?mm pellets using a uniaxial hydraulic press. Single step & two-step sintering methods were used to sinter the compacted pellets. Powders and sintered pellets were characterized for phase and microstructure using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM) technique. Rietveld method was used for quantification of obtained phases. The hardness of the sintered samples was evaluated by Vicker's hardness tester, and toughness was estimated by indentation fracture toughness method. Samples sintered using two-step sintering method shown optimum hardness and toughness (up to 1288 HV10 and 5.37?MPa?m^1/2) values compared to conventionally sintered samples because of reduced grain size.     

Reduction of Ti4+ to Ti3+ in Boron‐Doped BaTiO3 at Very Low Temperature

Reduction of Ti⁴⁺ to Ti³⁺ was found in boron‐doped BaTiO₃ ceramics when we sintered the samples at very low temperature (>850°C) in 5%H₂/Ar. Such reduction did not occur in pristine BaTiO₃ ceramic. The methods such as UV–vis spectroscopy, luminescence spectroscopy, and X‐ray photoelectron spectroscopy confirmed the reduction by showing the presence of Ti³⁺. The results of Ti–K‐edge X‐ray absorption near‐edge structure measurement (XANES) indicated that boron doping changed the geometry of Ti‐oxygen in BaTiO₃ to some extent. It was likely that some boron ions stayed at interstitial sites of BaTiO₃ lattice and acted as donors, which might trigger the reduction. The reduced boron‐doped BaTiO₃ were semiconducting and had very low room‐temperature resistivity (<100 Ω m). However, different from the n‐type rare‐earth‐doped BaTiO₃ ceramics, they did not display positive temperature coefficient resistance (PTCR) behavior.     

Effects of Cr content and morphology on the luminescence properties of the Cr-doped alpha-Al2O3 powders

Al₂O₃:Cr³⁺ samples were synthesized via hydrothermal and microwave solvothermal methods and thermal decomposition of Cr³⁺ doped precursors. The sample characterizations were carried out by means of X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD results indicated that Cr³⁺ doped samples were pure α-Al₂O₃ phase after being calcined at 1573 K. SEM results showed that the length and diameter of these Cr³⁺ doped alumina microfibers by hydrothermal route were about 2–5 μm and 100–300 nm, respectively; the obtained α-Al₂O₃ based powders via the microwave solvothermal method were microspheres with an average diameter about 1–2 μm. PL spectra showed that the Al₂O₃:Cr³⁺ samples presented a broad R band at 696 nm. It is shown that the 0.3 mol% of doping concentration of Cr³⁺ ions in α-Al₂O₃:Cr³⁺ is optimum. According to Dexter's theory, the critical distance between Cr³⁺ ions for energy transfer was determined to be 24 Å. It is found that the curve followed the single-exponential decay. Furthermore, the luminescence properties of the samples are also dependent on the morphology.     

Characterization of Magnesium‐Doped Hydroxyapatite Prepared by Sol‐Gel Process

Pure and doped hydroxyapatite (HA) nanocrystalline powders (Ca_10‐xMg_x(PO₄)₆OH₂) were synthesized using sol‐gel process. For this, calcium nitrate tetrahydrate, magnesium nitrate hexahydrate, and phosphorous pentoxide were used as precursors for Ca, Mg, and P, respectively. Calculated amounts of magnesium ions (Mg⁺²) especially from 0 to 10% (molar ratio) were incorporated as dopant into the calcium sol solution. The structure and morphology of the gels obtained after mixing the phosphorous and (calcium + magnesium) sol solution were different, and their condensations in time depend on the quantities of magnesium added. The several powders resulting from the gels dried and sintered at 500°C for 1 h were characterized by thermogravimetry (TG), Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), and inductively coupled plasma (ICP). Additionally, their agglomeration, morphology, and particle size were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The specific surface area of each sample was measured by the Brunauer–Emmett–Teller (BET) gas adsorption technique. The results of XRD, FTIR, and ICP values ranged between 0.45 and 2.11 mg/L indicated that the magnesium added in the calcium solution was incorporated in the lattice structure of HA so prepared, while those obtained by SEM and TEM confirmed the influence of Mg on their morphology (needle and irregular shape) and crystallite size, which is about 30–60 nm. The as‐prepared powders had a specific surface area ranged between 6.37 and 27.60 m²/g.     

Photoluminescence properties of Tb3+ doped Al2O3 microfibers via a hydrothermal route followed by heat treatment

Uniform Al₂O₃:Tb³⁺ microfibers were synthesized via a hydrothermal route and thermal decomposition of a precursor of Tb³⁺ doped ammonium aluminum hydroxide carbonate, and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), photoluminescence (PL) spectra and decay curves. XRD results indicate that various crystallographic phase Al₂O₃:Tb³⁺ microfibers are obtained by postannealing at different temperatures. SEM results show that the length and diameter of these Tb³⁺ doped α-Al₂O₃ microfibers are about 6–8 μm and 300 nm, respectively. The PL spectra indicate that the ⁵D₄ → ⁷F₅ (545 nm) electric dipole transition is the most intensive when excited at 240 nm. It is shown that the 2.0 mol% of doping concentration of Tb³⁺ ions in α-Al₂O₃:Tb³⁺ is optimum. According to Dexter's theory, the critical distance between Tb³⁺ ions for energy transfer was determined to be 12.7 Å. It is found that the decay curves follow the single-exponential decay.     

Facile synthesis of hollow F-doped SnO2 nanofibers and their efficiency in ethanol sensing

This paper reports for the first time the facile synthesis of hollow F-doped SnO₂ nanofibers by solution blow spinning (SBS) and their ethanol sensing performance. The as-prepared nanofibers were characterized using scanning electron microscopy (SEM), x-ray diffraction (XRD), Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FTIR), and electrochemical impedance spectroscopy (EIS). The gas sensing behavior of the F-doped SnO₂ nanofibers was investigated using a homemade test chamber. The results revealed the preparation of mesoporous F-doped SnO₂ hollow fibers with a diameter ranging from 207 ± 43 to 355 ± 41 nm. The combination of nanocrystalline hollow structure and F doping led to fast high-responsive ethanol sensors at room temperature (RT) with good reproducibility and long-term stability. These results indicate that F-doped SnO₂ hollow nanofibers are good candidates for building practical low-temperature ethanol gas sensors.     

Fabrication and properties of pressure-sintered reaction-bonded Si3N4 ceramics with addition of Eu2O3–MgO–Y2O3

Dense pressure-sintered reaction-bonded Si₃N₄ (PSRBSN) ceramics were obtained by a hot-press sintering method. Precursor Si powders were prepared with Eu₂O₃–MgO–Y₂O₃ sintering additive. The addition of Eu₂O₃–MgO–Y₂O₃ was shown to promote full nitridation of the Si powder. The nitrided Si₃N₄ particles had an equiaxial morphology, without whisker formation, after the Si powders doped with Eu₂O₃–MgO–Y₂O₃ were nitrided at 1400 °C for 2 h. After hot pressing, the relative density, Vickers hardness, flexural strength, and fracture toughness of the PSRBSN ceramics, with 5 wt% Eu₂O₃ doping, were 98.3 ± 0.2%, 17.8 ± 0.8 GPa, 697.0 ± 67.0 MPa, and 7.3 ± 0.3 MPa m^1/2, respectively. The thermal conductivity was 73.6 ± 0.2 W m^?1 K^?1, significantly higher than the counterpart without Eu₂O₃ doping, or with ZrO₂ doping by conventional methods.     

Enhancing the magnetic and antibacterial properties of ZnO nanopowders through Mn+Co doping

Undoped and doubly (Mn+Co) doped ZnO nanopowders were synthesized with different doping levels of Co (1, 2, 3, 4 and 5 at%) and constant Mn doping level (10 at%) using a simple soft chemical route. XRD profiles confirmed that the synthesized material is nanocrystalline ZnO with hexagonal wurtzite structure. No peaks other than the characteristic ZnO peaks were observed in the XRD pattern confirming the absence of any secondary phase. Antibacterial activities of synthesized ZnO nanopowders were tested against Staphylococcus aureus bacteria using agar well diffusion method. It was found that the antibacterial efficiency of the doubly doped ZnO nanopowders was remarkably high when the Co doping level was 5 at%. The obtained PL, SEM and TEM results are corroborated well with the antibacterial activity. Magnetic measurements showed that undoped ZnO sample exhibits diamagnetic behavior and as the Co doping level increases, the nanopowder behaves as a ferromagnetic material.     

Co-doping effects of A-site Y3+ and B-site Al3+ on the microstructures and dielectric properties of CaCu3Ti4O12 ceramics

Different doping elements have been used to reduce the dielectric losses of CaCu₃Ti₄O₁₂ ceramics, but their dielectric constants usually are undesirably decreased. This work intends to reduce their dielectric losses and simultaneously enhance their dielectric constants by co-doping Y³⁺ as a donor at A site and Al³⁺ as an acceptor at B site for substituting Ca²⁺ and Ti⁴⁺, respectively. Samples with different doping concentrations x = 0, 0.01, 0.02, 0.03, 0.05 and 0.07 have been prepared. It has been shown that their dielectric losses are generally reduced and their dielectric constants are simultaneously enhanced across the frequency range up to 1 MHz. The doped sample with x = 0.05 exhibits the highest dielectric constant, which is well over 10⁴ for frequency up to 1 MHz and is about 20% higher than the undoped sample. Impedance spectra indicate that the doped samples have much higher grain boundary resistance than the undoped one.     

Effect of milling type on the microstructural and mechanical properties of W-Ni-ZrC-Y2O3 composites

This study reports the effect of milling type on the microstructural, physical and mechanical properties of the W-Ni-ZrC-Y₂O₃ composites. Powder blends having the composition of W-1 wt% Ni-2 wt% ZrC-1 wt% Y₂O₃ were milled at room temperature for 12 h using a Spex™ 8000D Mixer/Mill or cryomilled in the presence of externally circulated liquid nitrogen for 10 min using a Spex™ 6870 Freezer/Mill or sequentially milled at room temperature and cryogenic condition. Then, powders were compacted in a hydraulic press under a uniaxial pressure of 400 MPa and green bodies were sintered at 1400 °C for 1 h under Ar/H₂ atmosphere. Phase and microstructural characterization of the milled powders and sintered samples were performed using X-ray diffractometer (XRD), TOPAS software, scanning electron microscope/energy dispersive spectrometer (SEM/EDS), X-ray fluorescence (XRF) spectrometer and particle size analyzer (PSA). Archimedes density and Vickers microhardness measurements, and sliding wear tests were also conducted on the sintered samples. The results showed that sequential milling enables the lowest average particle size (214.90 nm) and it is effective in inhibiting W grain coarsening during sintering. The cryomilled and sintered composite yielded a lower hardness value (5.80±0.23 GPa) and higher wear volume loss value (149.42 µm³) than that of the sintered sample after room temperature milling (6.66±0.39 GPa; 102.50 µm³). However, the sequentially milled and sintered sample had the highest relative density and microhardness values of 95.09% and 7.16±0.59 GPa and the lowest wear volume loss value of 66.0 µm³.