Influence of synthesis parameters on the physical properties of Cu3Se2 nanostructures using the sonochemical method

Copper selenide (Cu₃Se₂) nanostructures were grown by reaction of copper acetate and sodium selenide in a solvent of distilled water and ethanol at a temperature of 80 °C using the sonochemical method. In this study, the change of molarity, time, and power of ultrasonication waves was investigated on the physical properties of Cu₃Se₂ nanostructures. Cu₃Se₂ nanostructures were characterized by X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FESEM), Energy-dispersive X-ray spectroscopy (EDX), photoluminescence (PL), and UV–Vis spectroscopies. In this study the optimized conditions were selected as 30 min, 200 W, 1:2 for time, ultrasonic power, and molar ratio of Cu:Se, respectively. The XRD patterns and EDX results represent the formation of tetragonal Cu₃Se₂ phase and the presence of Cu and Se elements in the samples. FESEM images showed nanostructures in the form of spherical agglomerated particles. The results of the PL showed the effect of time, power, and molarity parameters on the appearance of different emission peaks. In all samples, the relative absorption ratio corresponded to the energy band gap such that with the increase in the time and power of ultrasound and the relative change in molarity, the relative absorption, and energy band gap were changed.     

Structural characteristics and optical properties of lead-free Bi(Zn1/2Ti1/2)O3-BaTiO3 ceramics

The xBi(Zn_1/2Ti_1/2)O₃-BaTiO₃ (xBZT-BT) ceramics, where x (mol) =0, 0.03, 0.06, 0.09, and 0.12, have been prepared by a solid-state reaction method. The phase transition, microstructure and optical properties were investigated. X-ray diffraction patterns indicate that the as-prepared samples have a polycrystalline perovskite structure. For x<0.06, the xBZT-BT ceramics exhibit clear tetragonal symmetry, and transform to rhombohedral phase as 0.06< x≤0.12. Coexistence of both tetragonal phase and rhombohedral phase is observed for x=0.06. The lattice strain is estimated by the Williamson-Hall analysis model, which suggests that the incorporation of substitution ions into the host lattice produces the inner stress field gives rise to structure distortions. The Raman scattering spectra corroborate the decrease in tetragonality with increasing the x, where the characteristic variation of phonon modes indirectly reveal the incorporation of Bi(Zn_1/2Ti_1/2)O₃. Furthermore, the optical band gaps of xBZT-BT ceramics show a non-linear change, which can be explained by the crystal field theory and phase structure effect.     

Influence of Al3+ on the cross relaxation process and electrical properties of Dy3+ activated Gd2O3 phosphor for white LED application

Gd₂O₃:Dy³⁺ Al³⁺ phosphors is synthesised by a wet-chemical method for various concentrations of Al³⁺ ion. X-ray diffraction, photoluminescence and impedance spectroscopy are used to understand the physio-chemical properties of the phosphors. The emission spectra of Dy³⁺ ion exhibit transition peaks centred at 572 nm (yellow), 486 nm (blue) and 669 nm (red). Energy transfer from Gd³⁺ to Dy³⁺ is also verified by exciting the phosphors at 274 nm. Some of the Dy³⁺ ions occupy both C₂ and S₆ site of Gd³⁺ ion in Gd₂O₃ matrix. It is also revealed that the enhancement of Dy³⁺ emission is strongly correlated to the surface morphology of the phosphors. Introducing Al³⁺ ions in Gd₂O₃:Dy³⁺ phosphor affect the emission properties of Dy³⁺ ions and its influence is explored at various concentration of Al³⁺ ions. The energy level diagram is presented to explain the cross-relaxation process among Dy³⁺ ions and the energy transfer from Gd³⁺ to Dy³⁺ ion.     

Influence of silicon carbide on structural,optical and magnetic properties of Wollastonite/Fe2O3 nanocomposites

The influence of adding 10, 20 and 30% molar ratio of silicon carbide (SiC) separately to a composite of wollastonite (W) with a fixed content of 10%Fe₂O₃ prepared by wet precipitation method was studied. The crystal structure of the annealed composite powders was inspected by X-ray diffraction (XRD); revealing multi-phase structure. The highest estimated crystallite size investigated by Scherrer equation of W, SiC, WFe:SiC₁₀, WFe:SiC₂₀ and WFe:SiC₃₀ were 53.89, 54.6, 56.3, 48.5 and 54.6 nm respectively; demonstrating the formation of nanocomposites. Particles shape, size and crystallinity of the samples were studied using high resolution transmission electron microscope (HR-TEM). The band gap E_g values of the nanocomposites increased with SiC content having an intermediate value that lies between that of γ-Fe₂O₃ (maghemite) and SiC. Ferromagnetic and paramagnetic contributions were observed in the magnetic hysteresis loops for the composites. This study highlighted that the coercive field (H_ci) of the composites improved with increasing the SiC content. The innovative wollastonite/Fe₂O₃/SiC with amended magnetic properties elicited attention due to their promising application in bone filler and industrial purposes.     

Electric field-induced changes in the ferroelastic behavior of (Na1/2Bi1/2)TiO3-BaTiO3

In this study, the macroscopic mechanical behavior was characterized for poled and unpoled polycrystalline (1?x)(Na_1/2Bi_1/2)TiO₃-xBaTiO₃ (NBT-xBT) for compositions across the morphotropic phase boundary (MPB). Due to a field-induced ferroelectric phase transformation, NBT-xBT compositions near the MPB (x?=?6–7?mol%) showed a significant decrease in the coercive stress for electrically poled samples. The apparent difference in mechanical behavior is suggested to be due to an irreversible electric-field-induced transformation to long-range ferroelectric order in the poled samples. The results indicate a significant difference in the critical stresses for the relaxor-ferroelectric transition and ferroelastic domain wall motion, which can have important effects on applications for lead-free ferroelectrics. To further illustrate this, a method was developed to electrically depole NBT-xBT at room temperature, resulting in an unpoled NBT-xBT material with long-range ferroelectric order. Mechanical testing revealed analogous macroscopic ferroelastic behavior to the poled samples, despite the lack of a piezoelectric response.     

The synthesis of rGO/RuO2, rGO/PANI,RuO2/PANI and rGO/RuO2/PANI nanocomposites and their supercapacitors

Polymer Bulletin - In this work, reduced graphene oxide (rGO) was obtained by chemical reduction of graphene oxide (GO) using sodium borohydride (NaBH4). Four different nanocomposites rGO/ruthenium...     

LDPE/Bi2O3 nanocomposites: Enhanced mechanical,dielectric, and optical properties

This study is focused on investigating the role of bismuth oxide (Bi₂O₃) nanoparticles to improve structural, optical, electrical, and mechanical properties of low-density polyethylene (LDPE). For this purpose, Bi₂O₃ nanoparticles were synthesized by using the solvothermal method and examined by transmission electron microscopes (TEM), x-ray diffraction (XRD), Fourier transformed infrared (FTIR) spectroscopy, and ultraviolet–visible (UV–Vis) light absorption methods. LDPE-based nanocomposites were prepared by changing the nanoparticle additive ratio in the composite from 0% to 2% by weight. The composites were analyzed in the context of their FTIR spectra, atomic force microscope (AFM) images, UV–Vis light absorption spectra, stress–strain curves, and energy storage abilities. While the AFM findings indicate a smoother surface for the composites, the optical band gap analysis reveals a slightly decreased direct optical band gap energy. The analyses based on dielectric spectroscopy also highlight the LDPE/0.5% n-Bi₂O₃ composite in terms of the best energy storage capability. Additionally, the highest Young's modulus, toughness, stress at break, and percentage of strain at break were also recorded for the LDPE/0.5% n-Bi₂O₃ composite. In this context, the LDPE/0.5% n-Bi₂O₃ composite with improved dielectric and mechanical properties can be suggested as a new promising LDPE-based nanocomposite with better properties for industrial purposes.     

Preparation and thermoelectric properties of MoS2/Bi2Te3 nanocomposites

MoS₂ nanosheets with size of several-hundred nanometers were prepared by a hydrothermal intercalation/exfoliation method, then MoS₂/Bi₂Te₃ composite nanopowders were prepared by a microwave-assisted wet chemical method using the MoS₂ nanosheets, TeO₂, Bi(NO₃)₃·5H₂O, KOH and ethylene glycol as raw materials. Bulk MoS₂/Bi₂Te₃ nanocomposites were prepared by hot pressing the MoS₂/Bi₂Te₃ composite nanopowders with MoS₂ nanosheet content ranging from 0 to 17 wt% at 80 MPa and 648 K in vacuum. X-ray photoelectron spectroscopy and X-ray diffraction analyses indicate that MoS₂ and Bi₂Te₃ did not react each other during the hot pressing. FESEM observation reveals that the MoS₂/Bi₂Te₃ composite samples had a more compact microstructure than the pristine Bi₂Te₃ bulk sample. The MoS₂ phase was relatively randomly dispersed in the composite. At a given temperature, the electrical conductivity of the composites increases first then decreases as the MoS₂ content increases, whereas the Seebeck coefficient of the bulk nanocomposites does not change much. A highest power factor, ~18.3 μW cm⁻¹ K⁻² which is about 30% higher than that of pristine Bi₂Te₃ sample, at 319 K has been achieved from a nanocomposite sample containing 6 wt% MoS₂.     

Electro-optic properties of Ba0.8Sr0.2TiO3 thin film

Electro-optic properties of Ba_0.8Sr_0.2TiO₃ (BST) film with a thickness of 1 μm deposited on the MgO (001) substrate by the rf sputtering have been studied. Structural features of the film were identified by X-ray diffraction method. It was shown, that the BST film exhibited a predominantly linear EO behavior under the applied static electric field, that have been explained according to the strong compressive stresses in the film. The polarization distribution across the gap between the electrodes when electric field is applied was also investigated experimentally and calculated. The linear EO coefficient of Ba_0.8Sr_0.2TiO₃ film with a thickness of 1 μm film was found to be r_c = 99.4 p.m./V, that is promising for various EO applications, for example, high performance EO modulator.     

Optical and ferromagnetic properties of hydrothermally synthesized CeO2/CuO nanocomposites

Nanostructured CeO₂/CuO composites are synthesized using a facile hydrothermal reaction. Results signify that Cu ions prefer to enter into CeO₂ lattice forming solid solution at low concentration, and would be transformed into CuO phase at moderate concentration. Moreover, the addition of CuO species into CeO₂ promotes the reduction of Ce⁴⁺ and the creation of oxygen vacancy (V_O) defects. Raman analyses confirm V_O concentration initially increases and then decreases with the increasing CuO phase and the sample Ce1Cu2 exhibits the highest defect concentration. The room temperature ferromagnetic behavior is observed firstly in CeO₂/CuO nonmagnetic system and the maximal saturation magnetization appears in Ce1Cu2. The emergent ferromagnetism appears to be relevant to the extensive V_O defects, which can be interpreted by the indirect double-exchange model. The synthetic interaction between CeO₂ and CuO results in the redshift of the bandgap in prepared CeO₂/CuO nanocomposites.     

Effect of Ca2+ site substitution on structural,optical, electrical and magnetic properties in Nd3+ and Mn2+-co-doped calcium molybdato-tungstates

Ca_1-3x-yMn_y[]_xNd_2x(MoO₄)_1-3x(WO₄)_3x molybdato-tungstates (? denotes vacant sites) were successfully synthesized by high-temperature solid-state reaction. New materials crystallize in scheelite-type structure within whole homogeneity range of solid solution (x ≤ 0.2000 and y = 0.0200). Morphological features and particle size distribution were investigated by SEM and laser diffraction methods, respectively. Spectroscopic measurements in the UV–vis range was carried out to determine optical direct band gap (E_g), Urbach energy (E_U) and confirmation of structural disorder. Refractive index (n) was calculated using four different models. Magnetic studies revealed paramagnetic behavior with long-range ferrimagnetic and short-range antiferromagnetic interactions. New materials showed weak n-type electrical conductivity and thermoelectric power factor (S²σ) that strongly depends on Nd³⁺ ions content. Dielectric parameters, i.e. relative permittivity (ε_r) and energy loss (tanδ) are insignificantly dependent on Nd³⁺ ions concentration. These effects were considered in terms of structural defects, thermal activation of charge carriers, and the Maxwell–Wagner polarization.     

Magnetic and optical properties of Nd/TiO2- rGO nanocomposites

Graphene, the thinnest 2-dimensional atomic material, is successively used as a composite material has it significantly improves optical, thermal, mechanical and electrical properties. Neodymium being a strong paramagnetic substance is capable of storing large amount of magnetic energy because of their greater number of unpaired electrons in their electron orbital structure. This paper focuses on the influence of graphene on the structural, optical and magnetic properties of rare earth neodymium (Nd) doped TiO₂ nanoparticles. Nd doped TiO₂ nanoparticles are deposited on reduced graphene oxide (rGO) sheets forming the nanocomposites by hydrothermal treatment. The nano size, structure and phase of the composites are analysed by X-ray diffraction and Raman spectra. Dispersion of pure TiO₂ and Nd/TiO₂ nanoparticles on the rGO sheets is studied with FESEM and HRTEM micrographs alongside the elemental composition confirmed by EDAX. Increased surface area and pore size analysis is revealed by BET isotherms and BJH data. Absorption edges are blue shifted owing to particle size and experimental conditions. PL and EPR spectra confirm the presence of paramagnetic defect centres in the nanocomposites. The M − H hysteresis curves of the composites reveal the ferromagnetic behaviour at room temperature.     

Eu3+ doped ferroelectric CaBi2Ta2O9 based glass-ceramic nanocomposites: Crystallization kinetics,optical and dielectric properties

We report Eu³⁺ doped transparent glass-ceramics (GCs) containing bismuth layer-structured ferroelectric (BLSF) CaBi₂Ta₂O₉ (CBT) as the major crystal phase. The CBT crystal phase was generated in a silica rich glass matrix of SiO₂-K₂O-CaO-Bi₂O₃-Ta₂O₅ glass system synthesized by melt quenching technique followed by controlled crystallization through ceramming heat-treatment. Non-isothermal DSC study was conducted to analyze crystallization kinetics of the glass in order to understand the crystallization mechanism. The optimum heat-treatment protocol for ceramization of precursor glass that has been determined through crystallization kinetics analysis was employed to fabricate transparent GCs containing CBT nanocrystals, which was otherwise difficult. Structural analysis of the GCs was carried out using XRD, TEM, FESEM and Raman spectroscopy and results confirmed the existence of CBT nanocrystals. The transmittance and optical band gap energies of the GCs were found to be less when compared to the precursor glass. The refractive indices of the GCs were increased monotonically with increase in heat-treatment time, signaling densification of samples upon heat-treatment. The dielectric constants (ε_r) of the GCs were progressively increased with increase in heat-treatment duration indicating evolution of ferroelectric CBT crystals phase upon heat-treatment.     

Effects of B2O3 substitution for Al2O3 on the crystallization and properties of translucent mica glass-ceramics

The effects of substituting Al₂O₃ with B₂O₃ on the structure, crystallization, mechanical properties, thermal properties and optical properties of translucent mica glass-ceramics were thoroughly investigated. The results demonstrated that the addition of 0.5 wt% B₂O₃ was optimum for glass precipitation, which increases the crystallinity of glass-ceramics and provides good translucency. When the content of B₂O₃ was greater than 0.5 wt%, both crystallinity and translucency decreased noticeably. The replacement of B₂O₃ for Al₂O₃ had no influence on the type of crystal phase and the precipitation of tetrasilicic fluoromica with non-stoichiometric ratio, while it did have an effect on the crystallinity and structure. The crystal sizes of glass-ceramics were in the nanoscale range and the transmittance test results indicated that they exhibit excellent translucency.     

Photovoltaic and UV detector applications of ZnS/rGO nanocomposites synthesized by a green method

The effect of graphene concentration on the photovoltaic and UV detector applications of ZnS/graphene nanocomposites was investigated. The nanocomposites were synthesized by a green, cost-effective, and simple co-precipitation method with different graphene concentrations (5, 10, and 15 wt%) using L-cysteine amino acid as a surfactant and graphene oxide (GO) powder as a graphene source. Transmission electron microscopy (TEM) images showed that the ZnS NPs were decorated on GO sheets and the GO caused a significant decrease in ZnS diameter size. The results of X-ray diffraction (XRD) patterns, Raman, and Fourier transform infrared (FTIR) spectroscopy indicated that the GO sheets were changed into reduced graphene oxide (rGO) during synthesis process. Therefore, L-cysteine amino acid played its role as a reducing agent to reduce the GO. Photovoltaic measurements showed that the graphene caused to increase the efficiency of solar-cell application of ZnS/rGO nanocomposites. In addition, our observation showed that the nanocomposites were suitable as ultraviolet (UV) detectors and graphene concentration increased the responsibility of the detectors.     

Effect of annealing temperature and graphene concentrations on photovoltaic and NIR-detector applications of PbS/rGO nanocomposites

The effect of annealing temperature on photovoltaic and near-infrared (NIR) detector applications of PbS nanoparticles (NPs) and PbS/graphene nanocomposites was investigated. The products were synthesized by a simple co-precipitation method and graphene oxide (GO) sheets were used as graphene source. Several characterization techniques were used to show transfer of the GO into reduced graphene oxide (rGO) during the synthesis process. In addition, the effect of graphene concentrations on morphology, structure, photovoltaic, and detector parameters of the samples were studied. Transmission electron microscope (TEM) images showed that, the PbS NPs were agglomerated, while, the PbS/rGO nanocomposites were dispersed completely after annealing under H₂/Ar gas atmosphere. UV–visible spectrometer showed an absorption peak for all samples in the near infrared red (NIR) region of the electromagnetic spectrum. The results indicated that, photocurrent intensity, responsivity of the samples to an NIR source, and solar-cell efficiency were affected by annealing of samples and graphene concentrations.     

Heat treatment effects on the structural and optical properties of thin Bi2(Se1-xTex)3 films

Thin layers of Bi₂-chalcogenides, in the form of Bi₂(Se_1-xTe_x)₃ films, were evaporated on glass substrates by means of the vacuum thermal evaporation. Microstructure of the as prepared layers was investigated by x-ray diffraction (XRD) analysis. Identifications of the surface morphology and roughness were determined via scanning electron microscope (SEM). Optical transmissivity spectra proved that the as prepared films have low transparency with growing trend upon increasing the wavelength beyond the infra-red region. Low transmittance was observed for the as prepared films. Heat treatment, in the form of temperature annealing, was carried out aiming at boosting the structural features and the materials transmissivity. Structural properties and surface features of the annealed films were probed also via XRD and SEM analyses. It was found that the crystal size increases while the micro-strain and the dislocation density decrease obviously due to annealing. It was also observed that the annealing process significantly enhances the materials transmission especially in the range of higher wavelengths. Optical band gap was studied after annealing at various temperatures. Notable change in the band gap value was observed as a result of annealing. The band gap of the undoped (Bi₂Se₃) materials showed significant rise from 0.14 to 1.79 eV due to annealing. Similarly, the Te-doped samples exhibited notable increase in their band gap values after annealing. For example, the optical band gap of the sample doped at x = 0.20 increased from 0.03 to 0.41 eV by annealing. On the other hand, transmittance was also enhanced by annealing. For samples treated at 250 °C for 3 h, their optical transmissivity is enhanced to over 99% at the visible near-IR range. Such significant enhancement can be ascribed to structural enhancements. With such enhancement in the optical transmissivity, optoelectronic applications including transparent electrode can be met.     

Structural and thermoelectric properties of hydrothermal-processed Ag-doped Fe2O3

Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) nanopowders with various Ag contents were synthesized at different hydrothermal reaction temperatures (150?°C and 180?°C). Their structural properties were fully investigated through an X-ray diffraction, a Fourier transform infrared spectroscopy, and an X-ray photoelectron spectroscopy. The hydrothermal reaction temperature, time, and Ag content remarkably affected the morphological characteristics and crystal structure of the synthesized powders. The Fe_2-xAg_xO₃ (0?≤?x?≤?0.04) powders synthesized at 150?°C for 6?h and the Fe_2-xAg_xO₃ (0.02?≤?x?≤?0.04) powders synthesized at 180?°C for 12?h formed the orthorhombic α-FeOOH phase with a rod-like morphology, whereas the Fe_2-xAg_xO₃ (0?≤?x?≤?0.01) powders synthesized at 180?°C for 12?h formed the rhombohedral α-Fe₂O₃ phase with a spherical-like morphology. The Fe_1.98Ag_0.02O₃ fabricated by utilizing Fe_1.98Ag_0.02O₃ powders synthesized at 180?°C showed the largest power factor (0.64?×10^?5 Wm^?1 K^?2) and dimensionless figure-of-merit (0.0036) at 800?°C.     

Influence of the selenization time on the properties of (Na0.1Cu0.9)2ZnSn(S,Se)4 thin films and their photovoltaic solar cells

(Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin films with a single kesterite phase were synthesized using a sol-gel spin-coating method accompanied by rapid post-annealing. In this study, we investigated the effect of selenization time on the crystal quality and photoelectric performance of the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ films. It was found that the crystallinity and morphology of the films was enhanced, and some of bigger Se substituted for the S site in (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ with increasing the selenization time. The bandgap of the film can be regulated from 1.04 eV to 0.99 eV by varying the selenization time. In addition, all films showed p-type conductive characteristics, and films with optimal electrical performance could be obtained by optimizing the selenization time. Finally, the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ thin film with the best crystal quality and optical-electrical characteristics was obtained at an optimized selenization time of 15 min. A high power conversion efficiency (PCE) of 3.92% was obtained for the (Na_0.1Cu_0.9)₂ZnSn(S,Se)₄ device, which is 42% higher compared to that of the undoped Cu₂ZnSn(S,Se)₄ (CZTSSe) device.     

Citrate-assisted hydrothermal synthesis of vanadium dioxide textured films with metal-insulator transition and infrared thermochromic properties

The present study reports the fast synthesis of VO₂ (М₁) oriented films on the r-Al₂O₃(012) substrates by the hydrothermal method using citric acid and vanadium (V) oxide as precursors with post deposition annealing in inert atmosphere. The effects of synthesis parameters (solution concentration and autoclave filling factor) on the films composition, morphology and electric properties are considered using XRD, Raman spectroscopy, AFM and SEM. The obtaining VO₂(M₁)/r-Al₂O₃ films show a metal-insulator transition with resistivity change of ~3.5 orders of magnitude and excellent thermochromic properties in the long-wavelength IR region. This work demonstrates a promising technique to promote the commercial implementation of VO₂ as material for design of infrared (IR) switch devices.