Effect of Cr Doping on Structural, Optical and Dielectric Properties of ZnO Nanoceramics Synthesized by Mechanical Alloying (original) (raw)
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Influence of Cr incorporation on structural, dielectric and optical properties of ZnO nanoparticles
Journal of Industrial and Engineering Chemistry, 2014
This study demonstrated the effect of Cr doping on structural, dielectric and optical behavior of ZnO nanoparticles synthesized through sol-gel method. Characteristic investigations have been carried out by X-ray diffraction, Field emission scanning electron microscope, Energy dispersive X-ray spectrometry, and Transmission electron microscope. The results confirmed the formation of nanoparticles in polycrystalline single phase with hexagonal wurtzite structure. The crystallite size has been found to vary around 20 nm. Dielectric studies were carried out by Impedance spectroscopy. The decrease effect of dielectric parameters with increase in dopant has been explained on the basis of Maxwell-Wagner model and Koops phenomenological theory. The impedance analysis suggested that the contribution of grain boundaries is dominating over grain contribution. A red shift in UV-vis spectra signified that band gap can be tuned by Cr doping from 3.32 to 3.22 eV because of the s-d and p-d exchange interactions.
Synthesis and Characterization of Cr Doped ZnO Nanocrystals
World Journal of Condensed Matter Physics, 2012
Samples of chromium doped ZnO were synthesized using co-precipitation technique at room temperature. Structural and optical properties of Cr doped ZnO samples were investigated by X-ray diffraction technique (XRD and UV-Visible spectroscopy (UV-Vis) respectively. X-ray diffraction (XRD) patterns confirm that the samples have hexagonal (wurtzite) structure with no additional peak which suggests that Cr ions go to the regular Zn sites in the ZnO crystal structure. The lattice constants were calculated using X-ray diffraction data and it is found that lattice parameters decrease with increasing Cr content. The average grain size was calculated using Scherrer's formula for pure and Cr doped ZnO samples and it is observed that grain size is in the range 11 to 17 nm. Band gap of Zn 1-x Cr x O samples has been evaluated using UV-Vis spectrometer. It is found that the band gap decreases as Cr increases; it is attributed to the s-d and p interactions and the smaller average grain size. It indicates that incorporation of Cr ions into the ZnO matrix. The chemical species of the grown crystals were identified by Fourier transform infrared spectroscopy (FTIR). From FTIR spectra it is observed that IR peaks corresponding to the Zn-O bands. Such results are presented in this paper quantitatively and qualitatively.
SSRN Electronic Journal
The role of Cr incorporation into the ZnO were probed through investigations into the structural, optical and magnetic properties. Zn1xCrxO with x = 0, 0.01, 0.03 and 0.05, nanoparticles were prepared by solution combustion method. Powder x-ray diffraction (XRD) results reveal, all the synthesized samples are in single hexagonal wurtzite crystal structures, indicating that Cr 3+ ions substitute the Zn 2+ ions without altering the structure. The crystallite size and microstrain were calculated using the WillamsonHall method and found to be 36 ± 2 nm for ZnO and it reduced with the increase of Cr dopant concentration to 20 ± 2 nm for Zn0.95Cr0.05O. Rietveld refinement analysis revealed that the lattice parameters a and c of ZnO are well matched with standard data (JCPDS #36-1451). The value of both a and c increases slightly with the increase in Cr concentration. Transmission electron microscopy (TEM) revealed that the particle size were 48 ± 2 nm, 29 ± 2 nm and 25 ± 2 nm for the Zn1xCrxO with x = 0, 0.03 and 0.05, respectively. TEM morphology indicated particles are agglomerated in the doped samples. The band-gap decreases slightly from 3.305 ± 0.003 eV to 3.292 ± 0.003 eV with increase of Cr content from x = 0 to 0.05, respectively. Photoluminescence measurements revealed the presence of defects in the samples, associated with zinc vacancies (Zn) and singly ionized oxygen vacancy (o +). The field-dependent magnetization M(H) measurements of ZnO and Cr-doped ZnO were carried out using a vibrating sample magnetometer (VSM) at 300 K. All the samples exhibits ferromagnetic behavior. This longrange ferromagnetism ordering observed in ZnO is explained based on bound magnetic polaron (BMP) mechanism. The o + vacancies playing a crucial role in observed room temperature ferromagnetism (RTFM) in ZnO. There is a sufficient amount of BMPs formed in Cr doped ZnO because of the defects (Zn) present in these samples. Therefore, the overlapping of BMPs results in the RTFM. However, the antiferromagnetic coupling at a higher doping concentration of Cr, weakens the observed RTFM.
Microstructural, optical and electrical properties of Cr-doped ZnO
Scripta Materialia, 2008
Undoped and Cr-doped ZnO polycrystalline samples were synthesized chemically. Optical measurements confirmed the presence of Cr in the ZnO lattice. Microstructural studies of bulk samples revealed a network of petal-like structures found to be unique to Cr-doped samples. Elemental mapping of these samples revealed uniform distribution of Cr and Zn atoms. Cr doping was seen to suppress the recombination radiation near 385 nm and increase the stability of ZnO films in O2 atmosphere.
Study Of Optical And Ferroelectric Behavior Of ZnO Nanostructures
Advanced Materials Letters, 2013
In the present work, we have synthesized ZnO nanostructures by sol-gel method in air at different selected sintering temperatures ranging from room temperature to 400 0 C and studied their structural, optical and ferroelectric properties. The synthesized samples are characterized by X-ray diffractrometer for structural properties and the optical properties are measured through UV-Visible spectrophotometer and Photoluminescence. The X-ray diffraction pattern indicates the pure phase formation of ZnO. Furthermore, photoluminescence spectra also confirm the formation of wurtzite structure of ZnO. X-ray diffraction (XRD) and Transmission Electron Microscope (TEM) studies show that the particle size of ZnO nanostructures increases with increasing the sintering temperature. The optical band gaps calculated through UV spectroscopy are found to be decreasing from 4.47 to 3.73 eV for samples sintered at room temperature to 400 0 C, respectively. Moreover, a weak ferroelectricity has been observed in ZnO nanostructures at room temperature through Polarization vs Electric field (P-E) loops.
Influences of Co doping on the structural and optical properties of ZnO nanostructured
Applied Physics A-materials Science & Processing, 2010
Pure and Co-doped ZnO nanostructured samples have been synthesized by a chemical route. We have studied the structural and optical properties of the samples by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), field-emission transmission electron microscope (FETEM), energy-dispersive X-ray (EDX) analysis and UV-VIS spectroscopy. The XRD patterns show that all the samples are hexagonal wurtzite structures. Changes in crystallite size due to mechanical activation were also determined from X-ray measurements. These results were correlated with changes in particle size followed by SEM and TEM. The average crystallite sizes obtained from XRD were between 20 to 25 nm. The TEM images showed the average particle size of undoped ZnO nanostructure was about 20 nm whereas the smallest average grain size at 3% Co was about 15 nm. Optical parameters such as absorption coefficient ( α), energy band gap ( E g ), the refractive index ( n), and dielectric constants ( σ) have been determined using different methods.
Cr-DOPED ZnO Prepared by Solid State Reaction Method
chemistry and materials research, 2017
In this paper, the effect of doped concentrations of Cr at ZnO powder has been studied using structur, magnetic and electrical properties has been investigated by X-Ray Diffractometer (XRD), Vibrating Sample Magnetometer (VSM), I-V and C-V measurements. The preparation of doped ZnO was using solid state reaction method with high speedshaker mill and continued with sintering at 900 0 C for 4 hours. Samples doped with Cr has polycrystalline hexagonal wurtzite structure with increasing Cr composition indicates the presence of impurity. From the results VSM of doping ZnO, Cr showed diamagnetic properties become paramagnetic. The results of the I-V and C-V meter Cr doped ZnO resistivity value increases ,decreases conductivity and dielectric constant decreases. Keywords : Cr , ZnO, Structur, Magnetic, Electrical properties
2014
The correlation between structural and optical properties of nanocrystalline ZnO synthesized by the citrate precursor method has been investigated. The Rietveld refinement of X-ray diffraction pattern confirms the P6 3 mc space group and formation of single phase hexagonal wurtzite structure with presence of tensile strain at the lattice site. The presence of Raman active optical phonon mode at 436 cm -1 which is a significant character of ZnO with hexagonal wurtzite structure supports the XRD result. FE-SEM result shows that the size of the particle is about 20 nm with nearly spherical shapes. The optical band gap energy at room temperature has been calculated as 3.28 eV using the Tauc plot technique. The UV-Vis sub-gap absorption curve supports the presence of strain inside the crystal. The photoluminescence spectrum indicates the dominancy of the defect related deep level or trap state emissions over the near band edge UV emissions using an excitation wavelength of 320 nm.
Effects of Chromium Doping on the Electrical Properties of ZnO Nanoparticles
2020
Nanostructured ZnO has gained a considerable amount of attention due to its unique physical and chemical properties and due to its remarkable performance in the fields of optics, photonics and electronics. The scope of this work is to study the Structural, Optical and Electronic properties of Pure Zinc Oxide (ZnO) and Chromium doped Zinc Oxide nanoparticles. These nanoparticles were synthesized by low-temperature precipitation method at various concentrations in the range (Zn 1-x Cr x O; (x = 0, 0.1& 0.3)). The precursors used were analytical grade Zinc Nitrate Hexahydrate and Chromium Nitrate Nona hydrate. The synthesized nanoparticles were annealed at 400 ° C. The Structural property of the synthesized nanoparticles was analysed by XRD (X-Ray diffraction) and was confirmed to exhibit a crystalline hexagonal wurtzite structure with an average crystallite size of 55nm. The functional groups were analysed using FTIR (Fourier Transformed Infra-red spectroscopy). The Morphology was ana...
2021
Cr doped ZnO (x = 0-0.04) nanoceramics was successfully synthesized by high energy ball milling (HEBM) technique. The structural and electrical properties of the synthesized sample has been studied in detail. The doping of Cr into ZnO has been verified by X-ray diffraction (XRD) and also from the variation in structural parameters. Rietveld refinement XRD pattern of calcined sample showed the hexagonal wurtzite structure and it did not induce impurity phases. From the XRD, it has been confirm that maximum result confirms that up to 4 atomic% of Cr can be doped into ZnO. The strain of the sample reduced with increase in particle size. After sintering, there is a growth of particle size of Cr doped ZnO sample. The impedance spectroscopy data shows a single semicircle in the high frequency region corresponding to the bulk properties of the nanoceramic sample. The decrease in real part of the impedance with temperature suggests the NTCR behavior of the sample in the temperature range of...