Polyaminocarboxylate promoted synthesis of Hafnium/ Zirconium substituted anion excess In2O3: Structure,optical and electrical conductivity properties

The current study aimed to generate Hf/Zr substituted In₂O₃ with the ultimate aim of realizing a potential transparent conducting oxide. We applied a co-complexation method to bring the reactively dissimilar In and Hf/Zr together in one oxide network. We prepared an EDTA complex containing an equimolar concentration of In and Hf/Zr and examined their characteristics with FTIR and TG-DSC traces. Rietveld refinement results of calcined complexes and their Raman spectra confirmed the formation of anion excess bixbyite structure for (In_1-xM_x)₂O_3+δ (M = Hf, Zr, and x = 0.50). The lattice expanded after substituting with Hf/Zr, and the optical bandgap increased from 2.87 eV (In₂O₃) to 3.20–3.60 eV. The high percentage reflectance in the visible region and absorbance in the UV region fulfilled some of the prerequisites of transparent conducting oxide. Electrical resistivity reduced up to two orders in magnitude with increasing temperature for Hf and Zr incorporated In₂O₃.     

Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La₄Ti₃O₁₂ were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO₃) phase and lanthanum oxycarbonate (La₂O_4·846C_0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO₃ (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La₄Ti₃O₁₂ (R-3-type space group). La₄Ti₃O₁₂ NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La₄Ti₃O₁₂ NPs provides a simple route to photocatalytic materials in reasonable quantities.     

Controllable syntheses of Mo5Si3 and Mo3Si by silicothermic reduction of MoS2 in the presence of lime

Molybdenum silicides (Mo–Si) have attracted great interest owing to their good electrical conductivity, ultra-high melting point and well oxidation resistance. In this work, the controllable syntheses of Mo₅Si₃ and Mo₃Si powders by silicothermic reduction of MoS₂ in the presence of lime are studied for the first time. The internal mixture composed of MoS₂ and Si is wrapped by sufficient CaO. After the reaction is finished, the synthesized molybdenum silicides can be easily separated from the desulfurization layer by peeling off the desulfurization product. The results show that Mo₃Si and Mo₅Si₃ can be prepared at 1500 °C for the samples with the MoS₂:Si molar ratio of 1:1.7 and 1:2.33, respectively. In addition, the results show that both SiS₂ and SiS can be formed during the heating process. The thermodynamic analysis about the disproportionation reaction of SiS indicates that the existence of SiS₂ depends on the partial pressure of SiS (P_SiS) and temperature. Moreover, it is demonstrated that SiS₂ is preferentially formed under low temperature conditions. As the temperature rises, it is much easier for SiS₂ to react with Si to form SiS. Additionally, this work experimentally proves for the first time that SiS gas can directly reduce MoS₂ to form MoSi₂ and SiS₂. Subsequently, the recovery of S in the desulfurization product was studied. S in MoS₂ was first captured by CaO in the form of CaS (accompanied by Ca₂SiO₄ and Si). In order to solve this CaS containing desulfurization product which is detrimental to the environment, CaS in the desulfurization product is react with Fe₂O₃ and C to form FeS. This work provides new insights into the closed-loop capture and recovery of S in the process of extracting metals or metal compounds from sulfide ores.     

Enhancement of Ca3Co4O9 thermoelectric properties by Cr for Co substitution

Ca₃Co_4−xCr_xO₉ polycristalline thermoelectric ceramics with small amounts of Cr have been synthesized by the classical solid state method. Microstructural characterizations have shown that all the Cr has been incorporated into the Ca₃Co₄O₉ structure and no Cr-containing secondary phases have been produced for Cr contents≤0.05. Apparent density measurements have shown that all samples are very similar, with densities around 75% of the theoretical one. Electrical resistivity decreases and Seebeck coefficient slightly raises when Cr content increases until 0.05 Cr addition. The improvement in both parameters leads to higher power factor values than the usually obtained by conventional solid state routes.     

Preparation of Nb-doped TiO2 nanopowder by liquid-feed spray pyrolysis followed by ammonia annealing for tunable visible-light absorption and inhibition of photocatalytic activity

Visible-light absorbing TiO₂ with color tunability and negligible photocatalytic activity was developed by synthesizing Nb-doped TiO₂ using liquid-feed flame spray pyrolysis (LF-FSP) followed by NH₃ annealing. Nb-doped TiO₂ nanopowders with selected Nb contents were synthesized by changing ratios of metalloorganic precursors. By using Ti and Nb precursors whose thermal decomposition behavior is very similar, the maximum Nb doping concentration was improved compared to Nb-doped TiO₂ prepared by flame spray pyrolysis (FSP) in previous reports. As-synthesized Nb-doped TiO₂ nanopowders were white regardless of the Nb content, while all became colored after NH₃ annealing. In addition, the color of Nb-doped TiO₂ after NH₃ annealing varied from yellow to dark green depending on the Nb content. Light absorption characterization indicates that the color variation is attributable to the localized levels formed by interstitial N-doping and Nb-doping-induced Ti³⁺ formation resulting from reduction by H₂, formed as a result of NH₃ decomposition.     

The characteristics of X1 type Y2SiO5:Tb phosphor particles prepared by high temperature spray pyrolysis

The X1 type Y₂SiO₅:Tb phosphor particles with high brightness were prepared by spray pyrolysis from spray solution with NH₄F flux material. The phosphor particles prepared by spray pyrolysis at high preparation temperature had spherical shape, fine size and dense morphology. The mean sizes of the phosphor particles prepared at 900 and 1650 °C were 1.3 and 0.9 μm. The emission spectrum of the phosphor particles prepared by spray pyrolysis at 1650^oC had the characteristics of X1 type Y₂SiO₅:Tb phosphor. The photoluminescence intensity of the phosphor particles directly prepared by spray pyrolysis from spray solution with 20 wt.% NH₄F flux of the product at temperature of 1650 °C was 127 and 184% of the X1 and X2 type Y₂SiO₅:Tb phosphor particles post-treated at 1100 and 1300 °C, respectively. The Y₂SiO₅:Tb phosphor particles prepared by spray pyrolysis at 1650 °C had X1 type crystal structure because of short residence time of particles inside hot wall reactor of 0.4 s.     

Effects of milling time and reductant content on the formation of HfC-HfB2 composite powders synthesized via a solid-state reaction route

In this study, a solid-state reaction route that is a combination of high-energy ball milling (HEBM) and annealing was adopted to synthesize HfC-HfB₂ composite powders. The effects of HEBM duration (0 h, 1 h, 2 h, and 4 h) and excess reductant (Mg or C) amount on the reaction mechanism of Hf–B₂O₃–C–Mg quaternary powder system were meticulously investigated. Following the HEBM of powder blends, annealing was performed at 1600 °C for 16 h under Ar atmosphere. A purification step was conducted the annealed powders by dissolving them in an acidic solution. X-ray diffractometry (XRD) technique revealed that a small amount of Hf and C powders reacted to form HfC phase after 2 h of HEBM. After annealing and purification, in addition to the HfC phase, the HfB₂ and HfO₂ phases were observed in the powders. Besides, the intensities of XRD peaks belonging to the HfO₂ phase gradually decreased, and those of HfC increased in the annealed and purified powders with increasing milling duration and reductant amounts. Both milled and milled-annealed-purified powders exhibited a decrease in the particle size with an increase in the HEBM duration. Transmission electron microscopy (TEM) micrograph belonging to 4 h milled-annealed-purified powders containing 50 wt% excess Mg and 50 wt% excess C revealed the formation of HfC-HfB₂ composite powders whose particles ranged between 50 nm and 100 nm.     

Characteristics of Ag powders coated with Pb-based glass material prepared by spray pyrolysis under various gas environments

Ag powders coated with Pb-based glass material for Si solar cell application are directly prepared by spray pyrolysis in various gas environments. Pb-based glass is successfully formed in the composite powders irrespective of gas environment. The composite powders have bimodal size distributions of nanometer and submicron sizes. However, the number of nano-sized powders decreases when the reducing gas was used as the carrier gas. The silver-conducting films fired at 700 and 800 °C have dense structures without pores irrespective of the gas environment in the preparation of the composite powders. Glass materials are uniformly segregated between micron-sized silver grains. The conducting film formed from the composite powders prepared under 20% H₂/Ar atmosphere have sheet resistance of 7.8, 6.8, 5.1 and 5.9 mΩ/sq at firing temperatures of 500, 600, 700 and 800 °C, respectively.     

Size-controlled Bi-based glass powders prepared by spray pyrolysis as inorganic additives for silver electrode

Bi-based glass powders as additive for silver conducting pastes were prepared by spray pyrolysis. The glass powders formed from the spray solution with low concentration of 0.025 M had bimodal size distribution with nanometer and submicron sizes. However, glass powders with spherical shape and narrow size distribution were prepared from the spray solutions with concentrations of 0.05 and 0.5 M. The mean size of the glass powders increased from 0.34 to 0.7 μm when the concentrations of the spray solutions changed from 0.05 to 0.5 M. The glass transition temperature of the glass powders with the mean size of 0.34 and 0.70 μm were 382 and 396 °C, respectively. The glass layers fired at 450 °C had clean surfaces irrespective of the mean size of the glass powders. Silver conducting films were formed by melting of the silver powders irrespective of the mean sizes of the glass powders at firing temperatures between 400 and 500 °C. The specific resistances of the silver conducting films change from 3.13 to 4.03 μΩ cm according to the mean size of the glass powders at a firing temperature of 500 °C.     

Fabrication and properties of dense silicon carbide ceramic via gel-casting and gas silicon infiltration

The dense Silicon Carbide (SiC) ceramics are fabricated by means of gel-casting and gas silicon infiltration (GSI) using carbon black and α-SiC as raw materials. We have successfully introduced a new initiator AIBA which is very suitable to aqueous gel-casting system containing carbon black, overcoming the problems posed by the conventionally used initiator. We have investigated the influences of the monomer acrylamide (AM) content, the ratio of the monomer to crosslinking agent AM/MBAM content, the particle size distribution and the solid content on the mechanical and structural properties of samples. The result show that, the linear shrinkage of the green body can be reduced to 1.0% and its bending strength can reach 59.2 MPa at the optimized gel-casting process that has an AM content of 25 wt%, an AM to MBAM ratio of 12, a SiC particle distribution of 3/2 and a solid content of 60 vol%. After the GSI process, the bending strength and elastic modulus of the final products from such green bodies can reach 245 MPa and 220 GPa respectively. The study highlights that the combined application of the gel-casting and the GSI processes can produce high-quality silicon carbide ceramics that are suitable in the space optical applications.     

Effect of annealing temperature on the morphology and optical properties of ZnO tetrapods grown by a thermal evaporation technique

The effect of the thermal annealing temperature was investigated on ZnO tetrapods grown by a thermal evaporation method. The ZnO tetrapods were synthesized by thermal evaporation of Zn powder in air. The annealing was done in an oxygen gas environment at temperatures ranging from 400 to 1000 °C for 1 h. As the annealing temperature increased from 400 °C to 800 °C, the morphology of the tetrapod remained unchanged; however, the size of the tetrapods increased. With a further increase in the annealing temperature from 800 °C to 1000 °C, the ZnO tetrapod changed drastically to nanoneedles. As-grown and annealed samples had an identical crystal structure, which was a wurtzite structure. A strong and sharp ultraviolet emission at 380 nm was observed for the 600 °C –annealed sample indicating the high crystalline quality. The ultraviolet emission intensity decreased abruptly for the samples annealed at 800 °C and 1000 °C, which exhibits the degradation in crystallinity.     

Studies on the Al2OC mesophase in synthesized AlN powder and its effects on properties of AlN ceramic substrates

A mesophase of Al₂OC was first determined in AlN powder synthesized in batch quantities via a carbothermal reduction nitridation (CRN) process. The formation and elimination mechanisms of the mesophase were investigated. Effects of the mesophase on properties of the AlN ceramic substrates were evaluated via bending strength and thermal conductivity tests of the substrates fabricated with AlN powder of different O contents. At the conditions of the synthetic furnace, i.e. T = 1700 °C, P_N2 = 10⁻⁵ kPa, and P_CO = 10^−0.008–10^0.973 kPa, the formation of Al₂OC is thermodynamically favorable. By increasing the flow rate of N₂ in the synthetic furnace, the formed Al₂OC was unstable and decomposed into AlN. The properties of the AlN substrates depend on the O content of the AlN powder. The thermal conductivity/bending strength of the AlN substrates increase or decrease, accordingly, based the O content of the reduced AlN powder. AlN substrates made of AlN powder with 0.84 wt% oxygen content show a thermal conductivity and bending strength of 176.3 W/(m·K) and 421.3 MPa, respectively.     

Enhanced electric and magnetic properties of (BiLi)1/2(Fe2/3W1/3)O3 multiferroic as compared to BiFeO3

Very low electric and magnetic moments are the two major disadvantages which restrict the practical applications of BiFeO₃. We have doped Li⁺ and W⁶⁺ in Bi³⁺ and Fe³⁺ site respectively to overcome the limitations of BiFeO₃. Pure BiFeO₃ and (BiLi)_1/2(Fe_2/3W_1/3)O₃ (BLFWO) are synthesized by a solid-state reaction technique. The samples are characterized by X-ray diffractometer, LCR meter, P–E loop tracer, vibrating sample magnetometer and dc resistivity setup to understand their different properties. Dielectric and impedance studies of the samples are measured at different frequency (10²–10⁶ Hz) in a wide temperature range (30–375 °C). Due to co-doping in pure BFO the remnant polarization and remnant magnetization are enhanced and thus BLFWO may show large industrial utility.     

Effect of defect states in the optical and magnetic properties of nanocrystalline NiO synthesised in a single step by an aerosol process

Nanocrystalline nickel oxide (NiO) was successfully synthesised as a phase-pure product from an inorganic precursor through a “single-pot”, gas-phase synthesis method, nebulised spray pyrolysis (NSP). Functional properties such as magnetic behaviour, luminescence and band gap were studied and compared with the properties of NiO powder synthesised by a conventional reverse co-precipitation process (RCP) which also needed an additional calcination step. Although NiO crystallised in the cubic (rocksalt) form, Rietveld analysis of X-ray diffraction data revealed the synthesised nanopowders to be in a distorted cubic (rocksalt) or monoclinic form. This distortion resulted from the antiferromagnetic exchange interaction energy and increased magnetic surface anisotropy, as seen from the bond lengths determined from Fourier transform infra-red (FTIR) studies. Raman spectroscopy also confirmed the distortion in the structure indicated by the presence of a first order phonon peak. The band gap decreased in case of both the powders and was attributed to the shallow donor or acceptor levels created due to the presence of defect states as determined from photoluminescence studies. The NSP powders also exhibited a dependence on the excitation wavelength during emission luminescence. A mixed antiferromagnetic and ferromagnetic behaviour was observed in the NSP powders and the susceptibility of each was deconvoluted through low and high field magnetometry studies. Further, the nanopowders from both the processes showed “core-shell” magnetism, with paramagnetic behaviour in the shell and antiferromagnetism in the core. The thicknesses of the core and shell were also determined.     

Characterization of SiO2-encapsulated WSi2/W5Si3 nanoparticles synthesized by a mechanochemical route

This study reports on the mechanochemical synthesis (MCS) of SiO₂-encapsulated WSi₂/W₅Si₃ nanoparticles starting from tungsten oxide (WO₃), silicon dioxide (SiO₂) and magnesium (Mg) powder blends. MCS process, carried out in a high-energy ball mill, was evaluated in terms of various milling time and initial composition of WO₃-SiO₂-Mg powders. A subsequent purification step using aqueous HCl solution was conducted on the as-synthesized powders. Compositional, microstructural and thermal properties of the powders were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and differential scanning calorimeter (DSC). Based on the adiabatic temperature values, SiO₂-encapsulated WSi₂/W₅Si₃ nanoparticles exhibit a high potential as a result of a mechanically induced self-sustaining reaction. The exothermic reaction took place after 20?min of milling, and WSi₂, W₅Si₃, W, MgO, Mg₂SiO₄ and residual Mg phases were detected. The utilization of an optimized amount of excess Mg (3.5?mol) resulted in the elimination of unwanted Mg₂SiO₄ and W phases, leaving behind WSi₂, W₅Si₃, Mg₂Si, MgO and Mg. After removal of Mg-based by-products by leaching process, WSi₂, W₅Si₃ and a very small amount of SiO₂ phases were obtained. TEM analysis revealed that W silicide nanoparticles with an average size of 97?nm were encapsulated by SiO₂ layers with an average thickness of 15?nm.     

Preparation and characterization of nanocrystalline La-doped ZnO powders through a mechanical milling and their optical properties

Structural and optical properties of mechanically milled La-doped ZnO powders are presented in this paper. The Zn_1−xLa_xO phase formed when x varied in a range of 0.02-0.06 and milled at 400 rpm for 20 h. The secondary La₂O₃ phase occurred with an increase of La content. The crystallite and particle size decreased as a function of La content as x = 0-0.14 due to the effect of Zener pinning and solute drag. The absorption edge shifted to a lower wavelength when La content was increased to x = 0.14 because of the size effect. The energy band gap of Zn_1−xLa_xO powders varied in a range of 2.96-3.12 eV depending on the crystallite size. The broad emission bands in a visible region centered at about 640 nm are attributed to oxygen deficiency.     

Preparation and infrared to visible upconversion luminescence of Yb2O3:Ho3+ nanocrystalline powders

Yb₂O₃:Ho³⁺ nanocrystalline powders were synthesized through a solid state reaction method. X-ray diffraction analysis and field emission scanning electron microscopy were used to analyze the phase composition and morphology of the powders. Then under the 980 nm excitation of laser diode, the fluorescence of the crystals was studied via a fluorescence spectrometer. The green and red emissions centered on 551 and 668 nm were observed, and the green band dominated the emission spectrum. The effect of the concentration of Ho³⁺ on the upconversion luminescence intensity was discussed and the possible upconversion emission mechanism was explained. It indicates that like other metal oxide nanoparticles, Yb₂O₃ could also be a potential host material for doping to prepare the upconversion phosphor.     

Synthesis of spherical shape borate-based bioactive glass powders prepared by ultrasonic spray pyrolysis

Spherical shape borate-based bioactive glass powders with fine size were directly prepared by high temperature spray pyrolysis. The powders prepared at temperatures between 1200 and 1400 °C had mixed phase with small amounts of fine crystal and an amorphous rich phase. Glass powders with amorphous phase were prepared at a temperature of 1500 °C. The mean size of the glass powders prepared by spray pyrolysis was 0.76 μm. The glass powders prepared at a temperature of 1200 °C had two distinct exothermic peaks (T_c1 and T_c2) at temperatures of 588 and 695 °C indicating crystallization. The glass transition temperature (T_g) of the powders prepared at a temperature of 1200 °C was 480 °C. Phase-separated crystalline phases with spherical shape were observed from the surface of the pellet sintered at a temperature of 550 °C. Crystallization of the pellet was completely occurred at temperatures of 750 and 800 °C. The pellets sintered at temperatures below 700 °C had single crystalline phase of CaNa₃B₅O₁₀. The pellet sintered at a temperature of 800 °C had two crystalline phases of CaNa₃B₅O₁₀ and CaB₂O₄.     

RT-XAMF and TR-XRD studies of solid-state synthesis and thermal stability of NaNiO2 as cathode material for sodium-ion batteries

Room-temperature sodium storage technology has been attracting considerable attention, and its potential as a alternative technology to lithium-ion batteries for electrical energy storage has been studied owing to the abundance of sodium resources and its inexpensiveness. In situ X-ray diffraction (XRD) techniques, such as real-time X-ray analytical micro-furnace (RT-XAMF) and time-resolved X-ray diffraction (TR-XRD), are utilized to identify the synthesis process and thermal stability of the NaNiO₂ cathode material for Na-ion batteries. Using the RT-XAMF technique, the solid-state reaction of Na₂O₂ and NiO was investigated in real-time to verify the phase transition from rhombohedral NaNiO₂ at temperatures above 243 °C to monoclinic NaNiO₂ at temperatures below 243 °C during heat treatment. In addition, the structural instability of the monoclinic NaNiO₂ phase changes to the Na-deficient Na_0.91NiO₂ phase. The TR-XRD technique was used to investigate the thermal stability of the desodiated Na_1?xNiO₂ (x = 0.09, 0.5) cathodes in the presence of an electrolyte. It was confirmed that the structural changes of desodiated Na_1?xNiO₂ were relatively simple compared to those of the Ni-based cathode material in Li-ion batteries. First, the layered structure of Na_1?xNiO₂ at room temperature turns into an MO-type rock salt phase (NiO) and subsequently into a metallic phase (Ni) without the appearance of spinel-type (Li_1?xM₂O₄ and M₃O₄) intermediates, which are typically observed in lithium nickel-based oxides. In addition, it was concluded that desodiated Na_1?xNiO₂ materials have higher thermal stability than delithiated Li_1?xNiO₂ (x = 0.5, below ～200 °C) based on its high decomposition temperature (～300 °C for Na_0.91NiO₂ and ～280 °C for Na_0.5NiO₂). From these results, we believe that our in-situ XRD findings on the real-time solid-state synthesis process and thermal stability can be used as a fundamental guide for the development of Ni-based NaMO₂ (M = Ni, Co, Mn, etc.) oxides for next-generation advanced Na-ion batteries.     

Fabrication of ultra-small SiC nanoparticles with adjustable size,stoichiometry and photoluminescence by AC multi-arc plasmas

Ultra-small SiC nanoparticles with sizes smaller than 10 nm have wide prospects in optoelectronics and biomedical engineering, but challenges in their synthetic methods still limit their practical applications. In this paper, an AC multi-arc plasma device was designed for the continuous gas-phase synthesis of ultra-small SiC nanoparticles. SiC nanoparticles with an average size range of 7–10 nm, abundant surface functional groups, and obvious photoluminescence emission were fabricated by the decomposition of triethylsilane in AC multi-arc plasmas. The synthesized SiC nanoparticles had a typical core-shell structure, whose core was mainly β-SiC and whose shell was covered by a few carbon layers. It was also found that the buffer gas effectively adjusted the particle size, crystal texture, stoichiometric ratio of each element, functional group composition, and photoluminescence. These adjustments were meaningful for the controllable preparation and practical utilization of ultra-small SiC nanoparticles. According to the product characteristics, the formation path of SiC nanoparticles and the influence of buffer gases were proposed.