Structure,luminescence and photocatalytic activity of Mg-doped ZnO nanoparticles prepared by auto combustion method

A series of Zn_1−xMg_xO nanoparticles with x=0 to 0.15 were prepared by auto combustion method using citric acid as the fuel and chelating agent. Structure, luminescence and photocatalytic properties were systematically investigated by means of X-ray diffraction, scanning electron microscopy, photoluminescence spectra, ultraviolet–visible absorbance measurement and photochemical reactions etc. The samples retained hexagonal wurtzite structure of ZnO and single phase below x=0.13, and the sizes of the nanoparticles were 60–70 nm. The photoluminescence spectroscopy demonstrated blue shift of ultraviolet emission with increasing Mg doping concentration. Both optical measurements of the as grown and Mg doped ZnO nanoparticles showed that the optical band gap could be modified from ~3.28 eV to 3.56 eV as the Mg content x increased from 0 to 0.13. The photocatalytic activities of the samples were evaluated by photocatalytic degradation of methyl orange, and the results showed that the doping of Mg into ZnO nanoparticles could enhance photocatalytic activity compared to the undoped ZnO nanoparticles, which was attributed to increased band gap and superior textural properties. In addition, according to the PL and photocatalytic studies, the critical doping content of effective Mg in ZnO is up to 0.09.     

Experimental and first-principles DFT studies of electronic,optical and magnetic properties of cerium–manganese codoped zinc oxide nanostructures

Syntheses, structural, optical and magnetic characterizations of codoped ZnO nanoparticles have been reported. Nanoparticles of Zn_1−2xCe_xMn_xO (x=0.00, 0.01, 0.02, 0.03, 0.04, and 0.05) were synthesized using a microwave-assisted combustion method. Structural, optical and magnetic properties were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), diffuse reflectance spectroscopy (DRS), photoluminescence spectroscopy (PL) and a vibrating sample magnetometer (VSM). The observed shift in XRD peak position, change in peak intensity, cell parameters, volume and stress confirmed the substitution of cerium-manganese (Ce–Mn) dopants within ZnO lattice. The synthesized nanoparticles show different microstructure without changing the parent hexagonal wurtzite structure of zinc oxide (ZnO). The average crystallites size was decreased from 43 to 21 nm. Energy dispersive X-ray spectra confirmed the presence of Ce and Mn in ZnO system and the weight percentage was nearly equal to their nominal stoichiometry. DRS analysis showed a decrease in the energy gap with increasing dopants content. The observed luminescence in the green, violet and blue regions strongly depends on the nature of the doping elements and their concentration owing to the formation of different oxygen vacancy, zinc interstitial, and surface morphology. Our results demonstrate that Mn ions doping concentration play an important role in the observed room temperature ferromagnetism (RTFM) of Ce–Mn codoped ZnO nanoparticles. First- principles calculation results indicate that Ce governs the stability, while Mn adjusts the magnetic characteristics in codoped ZnO.     

Effect of Co Doping on the Properties of ZnO Bulk Samples

In this study, Co-doped Zn_1?x Co _x O (x = 0.04, 0.06, 0.08, and 0.10, where x is the concentration of guest atom cobalt in the ZnO lattice) bulk samples were examined to determine the effect of doping on electronic, structural, magnetic, and optical properties. The samples were prepared using a standard high-temperature solid-state reaction technique. All samples were characterized by x-ray diffraction (XRD), magnetization measurements using vibrating-sample magnetometry (VSM), optical absorption spectroscopy, and scanning electron microscopy (SEM) with energy-dispersive x-ray spectroscopy (EDAX). The electron densities derived from the maximum-entropy method (MEM) show an improvement of electronic charge densities with Co impurity addition. The magnetic measurements at room temperature show variations in ferromagnetic behavior with respect to Co addition. The optical study shows a decrease in energy gap of ZnO with increasing cobalt content.     

Improving magnetic and structural properties of Zn1–xCuxFeCrO4 by substituting copper synthesized by citrate gel autocombustion route

The nanocrystalline Zn_1−xCu_xFeCrO₄ (x=0.0, 0.25, 0.50, 0.75 and 1.0) have been synthesized by citrate-gel autocombustion method. X-ray diffraction (XRD) confirmed formation of cubic spinel structure for all the compositions. The lattice constant (a) shows a decreasing trend with the increase in Cu content. Thermal analysis of precursor after autocombustion was carried out by using thermo gravimetric analysis (TG–DTA). Formation of spherical nanoparticles was revealed by transmission electron microscopy (TEM). The elemental analysis by SEM–EDAX was in close agreement with the expected composition of the starting composition used for the synthesis. The room temperature magnetic properties studied by using the vibrating sample magnetometer (VSM) indicate ferrimagnetic nature of the samples. The role of copper in the formation of modified structural and magnetic properties of these samples has been explained.     

Room temperature ferromagnetism in Cd1−xCrxTe diluted magnetic semiconductor crystals

Cd_1−xCr_xTe diluted magnetic semiconductor crystals were grown by vapor phase growth technique in the composition range of 0≤x≤0.05 and the effect of Cr doping on structural, morphological, optical and magnetic properties have been explored. X-ray diffraction analysis confirmed that all the grown crystals were zinc blende in structure without having any phase transition up to a Cr doping level of x=0.05. The lattice parameter decreased with increase in Cr doping level. Optical studies indicated that the optical band gap of the crystals decreased with the increase of Cr doping level. Magnetic properties were studied using vibrating sample magnetometer at room temperature and room temperature ferromagnetism was observed in all the Cr doped CdTe crystals.     

Photocatalytic and magnetic properties of Zn1−xCrxO nanocomposites prepared by a co-precipitation method

Polyvinyl pyrrolidone (PVP) capped Zn_1−xCr_xO (0.000001≤x≤0.1) nanocomposites were successfully synthesized using a simple chemical co-precipitation technique. The synthesized nanostructures were characterized by X-ray powder diffraction (XRD), transmission electron microscope (TEM), energy dispersive X-ray fluorescence (EDXRF), Fourier-transform infrared spectroscopy (FTIR), UV–visible spectroscopy, photoluminescence (PL) and vibrating sample magnetometer (VSM) measurements. The structural characterization by XRD, TEM, FTIR and EDXRF confirmed the formation of wurtzite structure and incorporation of Cr in the ZnO lattice. The photocatalytic activities of as prepared nanocomposites were evaluated by degradation of methylene blue (MB) dye in aqueous solution under UV/sunlight light irradiation. The results demonstrated that Zn_1−xCr_xO (x=0.0001) nanocomposite effectively bleached out MB, showing as impressive photocatalytic enhancement over pure ZnO and ZnS nanoparticles. This enhanced photocatalytic activity at optimum concentration was attributed to increased absorption ability of light and high separation rate of photoinduced charge carriers on the nanocomposite photocatalyst surface. The VSM measurements showed significant ferromagnetism in Cr-doped ZnO nanostructures and the value of saturated magnetism was found to decrease with increase in Cr content.     

Growth,X-ray peak broadening studies,and optical properties of Mg-doped ZnO nanoparticles

Undoped and Mg-doped ZnO nanoparticles (NPs) (Zn_1?xMg_xO, x=0.01, 0.03, and 0.05) were grown by the sol–gel method. X-ray results showed that the products were crystalline with a hexagonal wurtzite phase. Microscopy studies revealed that the undoped ZnO NPs and Zn_1?xMg_xO NPs had nearly spherical and hexagonal shapes. The size–strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the undoped and Mg-doped ZnO NPs. Some physical parameters such as strain, stress, and energy-density values were calculated for all reflection peaks of the XRD corresponding to the wurtzite hexagonal phase of ZnO in the 20–100° range from the SSP results. The effect of doping on the band-gap was also investigated by a photoluminescence (PL) spectrometer. The PL results showed that Mg²⁺ is a good dopant to control band gap of the ZnO properties.     

Preparation and Enhanced Thermoelectric Properties of p-Type BaFe12O19/CeFe3CoSb12 Magnetic Nanocomposite Materials

A series of p-type xBaFe₁₂O₁₉/CeFe₃CoSb₁₂ (x = 0, 0.05%, 0.10%, 0.20%, 0.40%) magnetic nanocomposite thermoelectric (TE) materials have been prepared by the combination of ultrasonic dispersion and spark plasma sintering (SPS). The effects of BaFe₁₂O₁₉ magnetic nanoparticles on the phase composition, microstructure, and TE properties of the nanocomposite materials were investigated in this work. x-Ray diffraction analysis shows that all the SPSed bulk samples are composed of main phase skutterudite besides a small amount of FeSb₂ and Sb. The TE transport measurements demonstrated that remarkable enhancements in electrical conductivity and Seebeck coefficient can be simultaneously realized by optimizing the doping content of BaFe₁₂O₁₉ magnetic nanoparticles. The lattice thermal conductivity was significantly reduced because of enhanced phonon scattering induced by BaFe₁₂O₁₉ nanoparticles. The highest ZT value reached 0.75 at 800 K for the sample with x = 0.05%, increased by 41.5% as compared with that of p-type CeFe₃CoSb₁₂ bulk material without BaFe₁₂O₁₉ magnetic nanoparticles. This work confirms that doping a small amount of BaFe₁₂O₁₉ magnetic nanoparticles can significantly improve the ZT value of p-type xBaFe₁₂O₁₉/CeFe₃CoSb₁₂ magnetic nanocomposite TE materials.     

Structural and magnetic studies of Ti4+substituted M-type BaFe12O19 hexa-nanoferrites

M-type hexagonal BaTi_xFe_12−(4/3)xO₁₉ nanoparticles, 0≤x≤1, were prepared by the chemical co-precipitation method. XRD, TEM, FT-IR, TGA, DTA and VSM techniques were used to characterize the samples. This study proved the formation of single-phase M-type hexagonal nanoferrites. The average particle and crystallite (R) sizes, lattice parameter c, experimental and theoretical densities, strain (ε), saturation magnetization (M_s), magnetic moment showed decrease against x, whereas the lattice constant a, porosity (P) and specific surface area showed increase. The force constants and trend of band positions and Debye temperature were x dependent, whereas the coercivity, remanent magnetization, squareness and anisotropy constant did not. The net weight loss of the samples led in the range of 0.00418–0.01834% weight where the maximum weight loss occurred before heating at 500 °C. P and R showed strong effect on M_s and ε.     

Effects of lanthanum and sodium on the structural,optical and hydrophilic properties of sol–gel derived ZnO films: A comparative study

The technological applications of the transparent ZnO films could be broadened via incorporation of small amounts of some special elements. In this work, the optical and surface properties of the spin coated Zn_1−xM_xO films (M=Na or La and x≤0.075) grown on glass substrates, are reported. According to X-ray diffraction (XRD) results, all films consist of a single phase with a hexagonal structure and the ZnO crystallites are preferentially oriented towards (002) direction. The plane surface of the pure ZnO film turned to be wrinkle network structure after Na and La addition. The reflectance (R%) of the films decreased after Na doping and significantly increased with increasing La content. The optical band gap of pure ZnO is 3.26 eV and red-shifted after Na and La incorporation. The dependence of the refractive index and film's wettability on the structural and morphological changes are reported. The obtained results of these two systems are compared with those of similar materials and some expected applications are explored.     

水热法制备CoxMn1-xFe2O4纳米磁性粉体及磁性研究

用水热法成功合成了CoxMn1-xFe2O4纳米磁性颗粒粉体。样品物相用X射线衍射仪表征,形貌通过透射电镜(TEM)观测。CoxMn1-xFe2O4纳米粉体的平均尺寸和晶格常数从XRD计算得到,CoxMn1-xFe2O4纳米颗粒的晶格常数随着Co2+含量的增加而变小。所得样品的磁性用振动样品磁强计(VSM)测试,结果表明,所制备的CoxMn1-xFe2O4粉体在室温下的铁磁性、饱和磁化强度和矫顽力随着Co2+含量的增加而变大。     

Hybrid deposition of piezoelectric (11\bar 20) MgxZn1−xO (0≤x≤0.3) on (01\bar 12) R-sapphire substrates using RF sputtering and MOCVDR-sapphire substrates using RF sputtering and MOCVD

Mg_xZn_1?xO (0≤x≤0.3) films are deposited on R-plane $(01\bar 12)$ sapphire substrates using a hybrid deposition technique: metalorganic chemical vapor deposition and radiofrequency (RF) sputtering. Thick piezoelectric Mg_xZn_1?xO films are deposited by RF sputtering on MOCVD grown thin ZnO buffers on R-sapphire substrate. Molar ratio of ZnO and MgO powders are mixed to form Mg_xZn_1?xO (0≤x≤0.3) sputtering targets with NiO (2–3 wt.%) added for compensation doping to achieve piezoelectricity. Field emission scanning electron microscopy shows that the deposited films are dense and uniform. X-ray diffraction indicates that the sputter-deposited Mg_xZn_1?xO (0≤x≤0.3) films retain the wurtzite crystal structure. The crystallinity of the deposited films is further improved by postannealing at 700°C in oxygen. Compositional analysis of the films is carried out using Rutherford back-scattering. High-frequency and low-loss surface acoustic wave (SAW) testing devices fabricated on these films are demonstrated. The SAW properties are tailored to changing Mg compositions. In the ZnO/R-Al₂O₃ system, two types of wave modes, the Rayleigh-type and the Love-type wave modes, are investigated.     

Synthesis,characterization and photo-catalytic studies of mixed metal oxides of nano ZnO and SnOx

Novel mixed metal oxides of Zinc and Tin (MZOTO) were synthesized by a simple co-precipitation method. The effect of blending varying compositions of SnO_x (x=1, 2) to ZnO has been evaluated, and it was found that the crystal structure, morphology, optical properties and photo-catalytic behavior were dependent on the percentage of SnO_x. The obtained samples were characterized using XRD, EDAX, FESEM, UV–vis spectroscopy, Photoluminescence, etc. XRD data revealed that the ZnO and SnO_x co-exist as mixture and their structures were found as hexagonal and cubic/orthorhombic respectively. FESEM image intricate about the morphology of the MZOTO prepared in 1:0.5 ratio providing nano flower structures that resemble like Chrysanthemum species. The band gaps of all the obtained MZOTOs were determined from UV–vis reflectance spectra using Kubelka-Munk relation. Photoluminescence emission studies revealed that the recombination of excited e⁻ with the h⁺ of ZnO is greatly influenced by SnO_x nanoparticles. Visible light photo-catalytic activities of MZOTOs were followed spectrophotometrically against the degradation of crystal violet solution. MZOTO2 obtained in the ratio of 1:0.5 shows better catalytic efficiency compared to other samples, degrading crystal violet completely within 40 min. The reusability and free radical trapping experiments were performed to study the performance and mechanism of MZOTO2 as the photo-catalyst. The photo catalytic efficiency of 1:0.5 MZOTO was higher due to the presence of flower-like structures that effectively captivated more photons from the sunlight.     

Role of intervalley scattering in the radiative recombination in Pb1 − x Eu x Te alloys (0 ≤ x ≤ 1)

Measurements of the photoluminescence from epitaxial layers of Pb_{1 ? x} Eu _x Te alloys with 0 ≤ x ≤ 0.32 are carried out. It is found that the luminescence intensity decreases with increasing Eu content and, already for x as low as about 0.1, drops by more than one order of magnitude. No luminescence is observed for 0.2 < x ≤ 0.32. This behavior is explained by the fact that, for x ≈ 0.1, the absolute minimum in the conduction band changes from the L to X point, which results in the scattering of nonequilibrium electrons to the X valley and, thus, causes a decrease in the quantum efficiency of the emission. According to published data, for x > 0.85, optical transitions also take place with the participation of the X valley; in this case, the emission is governed by the formation of magnetic polarons. The temperature dependences of the band gap are determined for 0 ≤ x ≤ 0.11. These dependences have a wide linear region characterized by a positive dE _g /dT coefficient, which decreases with the Eu content to become negative in pure EuTe.     

Magnetic properties of Pb1−x GexTe alloys doped with ytterbium

Temperature dependences of magnetic susceptibility and magnetic-field dependences of magnetization in the Pb_1?x?y Ge_xYb_yTe (0≤x≤0.02, y≤0.065) solid solutions were studied. It was found that diamagnetic response was replaced by the Curie-Weiss paramagnetic response as temperature decreased. This indicates that Yb³⁺(4f ¹³) magnetic ions are present in the alloys. The magnetic ion concentration and the occupancy of the Yb-induced impurity band were determined from the experimental data.     

Luminescent Si-Ge solid solution layers ER-doped in molecular-beam epitaxy

Erbium-doped Si_1?x Ge_x epitaxial layers have been grown by sublimation molecular-beam epitaxy (SMBE) in an atmosphere of germane (GeH₄). Doping with erbium was done during growth, with single-crystal Si:Er as the source of Er. The Si-Si_1?x Ge_x (0.01≤x≤0.09) interface was studied by secondary-ion mass spectrometry. Er and Ge show concentration profiles with abrupt boundaries and a significant decrease in their surface segregation. This means that hydrogen acts as a “surfactant.” Data on the luminescent properties of the Er-doped Si/Si_1?x Ge_x samples are reported.     

Features of conduction mechanisms in n-HfNiSn semiconductor heavily doped with a Rh acceptor impurity

The crystal structure and electron-density distribution, as well as the energy, kinetic, and magnetic characteristics of n-HfNiSn intermetallic semiconductor heavily doped with a Rh acceptor impurity in the temperature range T = 80–400 K, in the acceptor-concentration range N _A ^Rh ≈ 9.5 × 10¹⁹?1.9 × 10²¹ cm^?3 (x = 0.005–0.10), and in magnetic fields H ≤ 10 kG are investigated. It is established that doping is accompanied by a simultaneous decrease in concentration, the elimination of donor-type structural defects (to x ≈ 0.02), and an increase in the concentration of acceptor-type structural defects (0 < x ≤ 0.10). The dependence of the degree of semiconductor compensation on temperature is revealed. A model of the spatial arrangement of atoms in HfNi_{1 ? x} Rh _x Sn is proposed, and the results of calculating the electron structure based on this model agree with the results of investigations of the kinetic and magnetic characteristics of the semiconductor. The results are discussed within the context of the Shklovskii-Efros model for a heavily doped and compensated semiconductor.     

Preparation and characteristics of the wide gap semiconductor Mg0.18Zn0.82O thin film by L-MBE

The high purity ZnO ceramic target and the (MgO)_0.1(ZnO)_0.9 target were fabricated. The wurtzite-phase ZnO thin film and ternary Mg_xZn_1−xO thin film were grown on sapphire (0001) substrates by laser molecular beam epitaxy (L-MBE) from the sintered ceramic targets separately. The films' transmittance spectra at room temperature for the ZnO film and the Mg_xZn_1−xO film were measured and compared while their room temperature photoluminescence spectra were done. The band-gap modulation is realized from 3.31 eV for the ZnO film to 3.64 eV for the Mg_xZn_1−xO alloy film. The Mg content x in the Mg_xZn_1−xO alloy film was determined to be 0.18.     

Possible Enhancement of Thermoelectric Properties by Use of a Magnetic Semiconductor: Carrier-Doped Chalcopyrite Cu1−x Fe1+x S2

We focus on the chalcopyrite CuFeS₂ to utilize the interaction between carriers and magnetic moments of Fe as a possible source to achieve high power factor. Polycrystalline samples of Cu_1?x Fe_1+x S₂ were synthesized, and their thermoelectric properties are reported. Electrical resistivity decreased by two orders of magnitude with increasing x, while the Seebeck coefficient showed large values of ?200 μV/K at room temperature. Thermal conductivity also decreased with the increase of x. As a result, the power factor and the figure of merit, zT, of the carrier-doped samples are about 10 times larger than those of CuFeS₂. These observations suggest that magnetic semiconductors can make good thermoelectric materials.     

Microstructure and magnetic properties of In1−xCrxN thin films

Microstructure and magnetic properties of In_1−xCr_xN thin films grown on GaN-on-sapphire templates by molecular beam epitaxy are investigated. Optimized growth conditions are identified for the In_1−xCr_xN thin films at reduced growth temperature. The In_1−xCr_xN thin films on the top of the InGaN buffer layers exhibit high crystalline-quality. The magnetic properties of In_1−xCr_xN thin films show a ferromagnetic behavior even at room temperature.