Conventional HP sintering of asymmetric hexagonal structure Yb3+-doped Sr5(PO4)3F transparent ceramic without additives

The 2 at.% Yb³⁺:Sr₅(PO₄)₃F (S-FAP) polycrystalline transparent ceramic with asymmetric hexagonal structures has been synthesized by vacuum hot-pressing the nanoparticles prepared via coprecipitation method. X-ray diffraction results of powder and ceramic indicate that their phase peaks are well matched to the crystal structure of S-FAP. The average particle size of 35.5 nm has been exhibited by powder scanning electron microscopy images, and subsequent images of the ceramic cross section and surface morphology revealed a homogenous and compact microstructure with an average grain size of around 220 nm. The relationship between the optical loss caused by the scattering of anisotropic ceramic grains and the optical transmittance of ceramics was revealed in the hexagonal S-FAP transparent ceramics with different thicknesses. The in-line transmittance of hot-pressed ceramics with 1.5-mm thickness achieved 79.95% at 1100-nm wavelength, and the room-temperature absorption and emission spectra of Yb³⁺ in S-FAP polycrystalline ceramic matrix were measured using a spectrofluorometer.     

Tetramethylammonium based lead free perovskite active layer for solar cell application

Here we report the synthesis of a novel lead free organic-inorganic halide perovskite layer, tetramethylammonium tin tri-iodide (TMASnI₃), by simple and cost-effective chemical synthesis technique. The microstructural and optical studies confirm the formation of hexagonal perovskite structure with optical band gap ∼2.44 eV. A solar cell structure is fabricated by depositing the perovskite layer on zinc oxide thin film to demonstrate stable photovoltaic response under solar spectrum, where a thin layer of graphene oxide flakes on top of the perovskite layer acts as the charge transport layer. The open-circuit voltage (V_oc) and short circuit current density (J_sc) for this cell as extracted from the current-voltage measurement under one sun illumination of AM1.5 solar radiation are 0.60 V and 8.65 mA/cm², respectively. Without using any conventional hole transport layer, the power conversion efficiency (η) has been obtained as 1.92% which indicates the suitability of this perovskite material as an active layer for perovskite solar cell.     

Preparation and characterization of V2O3 micro-crystals via a one-step hydrothermal process

Phase pure V₂O₃ micro-crystals with a hexagonal dipyramid morphology were fabricated for the first time via a facile one-step hydrothermal method. The crystals were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and differential scanning calorimetry (DSC). A hexagonal dipyramid structure of V₂O₃ enclosed by well-grown {012} facets was obtained by hydrothermally reducing VO(acac)₂ precursor with N₂H₄·H₂O at 220 °C for 48 h. The results indicated that V₂O₃ can be well crystallized up to micron size with distinguished facets by only one step hydrothermal treatment. The formation mechanism and morphology evolution for V₂O₃ micro-crystals were discussed. Based on our experiments, the V₂O₃ nuclei formed and grew by a phase transformation through a dissolution–recrystallization process of VOOH, and the formation of the hexagonal dipyramids was ascribed to the specific adsorption of Hacac to the {012} facets restraining the growth in the directions normal to the {012} facets. The present work provides a facile method for preparing phase pure V₂O₃ micro-crystals with hexagonal dipyramid morphology, which can be used as a new powder material for ceramic fabrication.     

Aqueous Co-precipitated spherical shape PbZrO3 nanopowders: Perovskite phase formation

The perovskite phase formation of nanocrystalline powder of lead zirconate (PbZrO₃, PZ) was investigated. The structure, phase formation and morphology of PZ powders were characterized using the X-ray diffraction technique (XRD), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, transmission electron microscope (TEM) and differential scanning calorimetry (DSC). Tetragonal zirconia (t-ZrO₂) phase was found as an intermediate phase during the calcinations process, followed by the crystallization of the orthorhombic PZ phase. The change in relative amount of the residual t-ZrO₂ phase as a function of calcination temperature was estimated from the relative intensities of selected Raman peaks. From a TEM photograph, the PbZrO₃ powder was found to be spherical in shape with uniform nanosized features. The average particle size for the calcined powders was about 10.44±1.21 nm.     

Preparation of Morphology‐Controlled Plate‐Like Sodium Niobate Particles by Hydrothermal Synthesis

Sodium niobate (NaNbO₃) particles with plate‐like morphology and hexagonal unit cells were prepared by the hydrothermal method. The result of SEM showed that the hexagonal NaNbO₃ were characterized by plate‐like morphology with a diameter of 5–15 μm and a thickness of 1–2 μm. The crucial influences on the morphology and crystal phase of the NaNbO₃, such as concentration of [OH^?], surfactant, and K⁺:Na⁺ ratio, were established. By further calcination treatment, the plate‐like hexagonal NaNbO₃ particles could be completely transformed into perovskite structure without morphology change. The XRD and EBSD results indicate that the major face of the calcined particles is parallel to the crystallographic (001)_pc (pseudo cubic index) plane. Compared with the traditional high‐temperature molten salt method, this work provides a simpler way to prepare the template for fabricating textured ceramics.     

Synthesis of NdAlO3 with good microwave dielectric properties by stearic acid method

In this study, NdAlO₃ with perovskite structure was synthesized by the stearic acid method at relatively low temperature. The structural characteristics of the as-synthesized product were identified by TG–DSC, XRD, FT–IR, SEM, and TEM techniques. Using the powders as starting materials, NdAlO₃ bulk microwave ceramics were prepared, and the corresponding densification process, microstructural and dielectric properties were studied. The XRD and FI–IR results confirmed that single phase NdAlO₃ could be prepared at low temperature by the stearic acid method. A unique two-dimensional platelike morphology with an unevenly dispersed bubble shape structure was observed in the calcined powder. However, the TEM result revealed that the powder calcined at 800 °C had a good dispersity accompanied with narrow particle size distribution within a range of 20–35 nm. The average particle size of 27.3 nm was in accordance with that calculated from the XRD data. Using the powder calcined at 800 °C as raw materials, the as-obtained NdAlO₃ ceramics sintered at 1500 °C for 4 h possessed the highest density and favorable combined microwave dielectric properties (i.e., ε_r = 23.02, Q × f = 65320 GHz, and τ_f = −32.4 ppm/^°C). The present work developed a fast, energy-efficient approach to synthesize NdAlO₃ powder used as promising raw materials of microwave dielectric ceramics.     

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.     

Direct synthesis of CeO2/SiO2 mesostructured composite materials via sol–gel process

A series of CeO₂/SiO₂ mesostructured composite materials was synthesized by sol–gel process using Pluronic P123 as template, tetraethylorthosilicate as silica source and hexahydrated cerium nitrate as precursor under acid condition. The as-synthesized materials with Ce/Si molar ratio ranging from 0.03 to 0.3 were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), laser Raman spectroscopy (LRS), and N₂ adsorption. Characterization revealed that all samples possess ordered hexagonal mesoporous structure similar to SBA-15 and possess high surface area, large pore volume and uniform pore size. The fact that cerium species are present as highly dispersed CeO₂ nanocrystals in hexagonal matrix was confirmed by XRD combined with high-resolution TEM and selected area electron diffraction (SAED) analysis. Introduction of ceria to silica matrix can cause a distortion of hexagonal ordering structure and decrease pore diameter and increase the wall thickness of mesopores. Moreover, it can be found that this sol–gel route is a feasible, effective and simple method for templating synthesis of CeO₂/SiO₂ composite materials.     

H2-Production on New BaTi(1−x)RhxO3 Catalyst via the Steam Reforming of CH4 for H2-SCR Applications

Rh-doped perovskites BaTi_0.9Rh_0.1O₃ and Rh–BaTiO₃ were prepared by a new synthesis method and analyzed by XRD and FE-scanning electron microscopy (SEM). The effect of HCl for sol-formation was studied, HCl improves the sol formation but chlorine remains in the catalyst even after calcination treatment at 1,000 °C. Cl-free catalysts were prepared and analyzed on reactions for H₂ production which can be used for H₂-SCR reactions. The Rh-integrated perovskite BaTi_0.9Rh_0.1O₃ displayed better catalytic performance compared to Rh–BaTiO₃ and Rh–TiO₂ under the studied reaction conditions. Carefull XRD analysis was carried out to demonstrate the incorporation of Rh in the perovskite lattice. Rhodium reacts with the tetragonal perovskite BaTiO₃ to stabilize the hexagonal modification. Mainly, the hexagonal perovskite was found in the catalyst BaTi_0.9Rh_0.1O₃. This modification appears only after Rh-impregnation and calcination of the tetragonal BaTiO₃ thus coexisting the hexagonal perovskite BaTi_(1?x)Rh_xO₃ and the tetragonal BaTiO₃. The catalysts reduction in diluted H₂ containing gas mixtures cause the segregation of Rh° nanoparticles out of the perovskite crystal lattice.     

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.     

Synthesis of hexagonal pyramidal columnar hematite particles by a two-step solution route and their characterization

Hexagonal pyramidal columnar hematite (α-Fe₂O₃) particles have been synthesized by a hydrolysis method using iron sheets and nitric acid of mildly acidic pH at 90 °C. The morphologies and structures of the resulting products have been characterized by transmission electron microscopy (TEM) and field-emission scanning electron microscopy (FESEM), X-ray powder diffraction (XRD), and Fourier-transform IR spectroscopy (FTIR). An aggregation growth mechanism is proposed to rationalize the formation of α-Fe₂O₃. The influence of pH on the structure and morphology of the as-prepared α-Fe₂O₃ has been investigated. Additionally, magnetic investigations have shown that the hexagonal pyramidal columnar α-Fe₂O₃ exhibited weak ferromagnetism at room temperature.     

Phase development in Ba(Mg1/3Ta2/3)O3 via conventional and B-site precursor routes

Phase-formation stages in Ba(Mg_1/3Ta_2/3)O₃, prepared by conventional and B-site precursor methods, were investigated and the results are compared. Appropriate powder mixtures were heat-treated at selected temperatures and characterized by X-ray diffraction (XRD) in order to examine the phase development. In the conventional route, monophasic perovskite, finally resulted at high temperatures, had several preliminary intermediate phases, whereas in the B-site precursor method the perovskite formed directly from the reactants. The perovskite formation using B-site precursors was completed at significantly lower temperatures.     

Laser absorption and infrared stealth properties of Al/ATO composites

In this work, an Al powder was coated with antimony-doped tin oxide (ATO) to obtain an infrared-laser compatible stealth material. The composites are prepared via a coprecipitation method, characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), and measured by ultraviolet spectrophotometer and dual band infrared emissometer. The morphology and microstructure show that the flaky Al powder was coated by the ATO nanoparticles and doped into the SnO₂ rutile structure by an Sb⁵⁺ ion_. The optimal Al content was 20%, and the optimized Sn/Sb molar ratio was 10: 1. Meanwhile, the reflectivity of the composites was 43.454%, and the infrared emissivity in 8–14 μm far infrared waveband range was 0.708. It may shed light on a new material design orientation to obtain high performance laser-infrared compatible stealth materials.     

Solid state metathesis synthesis of BaTiO3, PbTiO3, K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3

A solid state metathesis approach has been applied to synthesize perovskite oxides such as BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and Na_0.5Bi_0.5TiO₃, these were characterized by powder XRD, IR and energy dispersive spectra (EDS). Potassium titanium oxalate and metal chlorides are used as the starting materials. X-ray analysis shows the formation of a single phase with tetragonal structure for BaTiO₃, PbTiO₃, K_0.5Bi_0.5TiO₃ and a monoclinic structure for Na_0.5Bi_0.5TiO₃. The Infrared spectra of these compounds show the characteristic band due to Ti–O octahedron for all the compounds. The EDS spectra show the relative ratio of the metal ions. The morphology of synthesized compounds was obtained from SEM measurements.     

Films and crystalline powder of BiI3 intercalated with ammonia

Intercalation, i.e. the insertion of guest species in a crystalline layered structure, is an efficient route for generating new materials with novel properties. Thin films and crystalline powder of BiI₃ layered semiconductor were intercalated by exposure to ammonia vapors at room temperature. The intercalated compound was studied by thermo-gravimetric analysis, differential scanning calorimetry, X-ray diffraction, UV–vis optical absorption, FTIR spectroscopy and Raman scattering. After exposure of BiI₃ to ammonia the formation of a new phase, BiI₃(NH₃)_3.83, was evidenced by thermal analysis. The intercalation process leads to a blue shift of the BiI₃ optical absorption edge by 0.5 eV. The appearance of new Raman lines at 135 and 353 cm^?1 in the Raman spectrum of intercalated BiI₃ is considered as an evidence of the chemical interaction between the ammonia molecules and BiI₃ lattice.     

Low Temperature Synthesis of Carbonate‐Free Barium Titanate Nanoscale Crystals: Toward a Generalized Strategy of Titanate‐Based Perovskite Nanocrystals Synthesis

Synthesis temperature and purity of perovskite materials are key challenges facing the scientific community. This work aims to address these challenges by developing an innovative low temperature synthesis pathway for preparation of carbonate‐free perovskite nanocrystals. The method is based on an ultrasound‐assisted wet chemical processing method. Nanocrystals are characterized and observed by X‐ray diffraction (XRD), field‐emission scanning electron microscopy and high‐resolution transmission electron microscopy techniques. XRD studies show that very fine BaTiO₃ nanocrystals (<11 nm) free from any by‐products such as BaTi₂O₅ and BaCO₃ are synthesized at 50°C. Moreover, the method developed here can be used as a strategy for synthesizing carbonate‐free perovskite nanocrystals. We believe that the method developed in this work provides a simple, cost‐effective, and convenient route for synthesizing a variety of perovskite materials for assembling in nanotechnology.     

Structural,morphological, optical,cation distribution and Mössbauer analysis of Bi3+ substituted strontium hexaferrite

Single-phase M-type hexagonal ferrites, SrBi_xFe_12−xO₁₉ (0.0≤x≤1.0), were prepared by a co-precipitation assisted ceramic route. The influence of the Bi³⁺ substitution on the crystallization of ferrite phase has been examined using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and Mössbauer spectroscopy. The XRD data show that the nanoparticles crystallize in the single hexagonal magnetoplumbite phase with the crystallite size varying between 65 and 82 nm. A systematic change in the lattice constants, a=b and c, was observed because of the ionic radius of Bi³⁺ (1.17 Å) being larger than that of Fe³⁺ ion (0.64 Å). SEM analysis indicated the hexagonal shape morphology of products. From ⁵⁷Fe Mössbauer spectroscopy data, the variation in line width, isomer shift, quadrupole splitting and hyperfine magnetic field values on Bi substitutions have been determined.     

A novel 3D network nanostructure constructed by single-crystal nanosheets of B4C

Three-dimensional (3D) network nanostructure boron carbide was successfully synthesized via the carbothermic method. The carbon source and template was carbonized bacterial cellulose (CBC) with a 3D network nanostructure, and the boron source was B₂O₃ and amorphous B powder. X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray photoelectron spectra (XPS) were used to study the morphology and structure of the samples. XRD and Raman spectra confirm that they belong to the B₄C crystalline phase. The FESEM images show that the synthetic B₄C retains the 3D network nanostructure of the template CBC well and consists of B₄C nanosheets with an average thickness of less than 100 nm. The analytical results of high-resolution TEM (HRTEM) and Selected Area Electron Diffraction (SAED) indicate that the B₄C takes the shape of hexagonal single crystals with a rhombohedral structure. These B₄C single crystal nanosheets alternate, forming the 3D network nanostructure. The mechanism of formation can be accounted for by in situ reduction reactions along the carbon nanofibers of CBC.     

Synthesis and Characterization of New Zinc(II) Coordination Polymer with a Flexible Hetro-coordination Ligand via In Situ Reaction as a New Precursor for Zinc(II) Oxide Nano-sphere Particles

A new coordination polymer, [Zn₃(tza)₃(H₂O)₃] _n (1) which H₂tza?=?1H-tetrazolate-5-acetic acid has been synthesized and characterized by IR spectroscopy, elemental analysis X-ray crystallography. The single-crystal X-ray data of compound 1 show existence of three different ZnII ion with different coordination spheres, hexagonal, pyramidal and pentagonal. This coordination polymer used as a precursor for preparation of zinc(II) oxide nano-particles. Nano-particles were characterized by powder X-ray powder diffraction and the its morphology characterized by scanning electron microscope.     

Facile Synthesis,Characterization, Catalytic and Photocatalytic Activity of Multiferroic BiFeO3 Perovskite Nanoparticles

We report the synthesis of multiferroic BiFeO₃ perovskite nanoparticles using the microwave combustion technique. Phase evolution is investigated by XRD, which confirms that the formation of a secondary α-Bi₂O₃ phase with a monoclinic structure along with the existing rhombohedral (BiFeO₃) structure. The average crystalline size has been found at 50 nm. The optical band gap was calculated from the Tauc’s plot it has been found 2.18 eV. The appearances of FT-IR spectra revealed bands at 550 and 444 cm^?1 were correlated to the rhombohedral stretching modes of BiFeO₃ nanostructure. The surface morphology showed the formation of nanosized grains with pores. The magnetization-Field (M-H) hysteresis curves revealed the appearance of ferrimagnetic behavior at room temperature. The BET surface area of BiFeO₃ perovskite nanoparticles was found 44.86 m²/g. The as-fabricated BiFeO₃ perovskite nanoparticles were investigated for their superior catalytic activity in two applications, which include (i) Glycerol to formic acid oxidation in the liquid phase with a high efficiency of over 98 percent, (ii) Under visible light, the photocatalytic breakdown of rhodamine B achieved maximal efficiency (almost 99 percent). Finally, we concluded that the BiFeO₃ perovskite nanoparticles exhibit high performance in future multifunctional devices is demonstrated by the simultaneous enhancement of catalytic and photocatalytic activities.