Doped NiO Samples Research Articles

Synthesis, Structural, Optical and Electrical Properties of Pure and Doped NiO Nanostructures Prepared via The Co-precipitation Method

Here, we report the synthesized high purity NiO nanostructures using simple and inexpensive chemical route. NiO NPs and (Cu, Zn) single and dual doped NiO NPs prepared by co-precipitation technique and annealed at 350 ℃ for 2 hours. Structural properties of prepared samples were investigated by X-ray diffraction (XRD). The optical characterizations and electrical conductivity were characterized by UV-vis spectrophotometer and I-V measurement. The crystallite size for dual doped NiO samples was 7.9 ± 0.9 nm compared to pure NiO, which had 9.52 nm. These results are consistent with the ionic radii of the doped metals. The obtained values of the band gap energy increased from 3 eV for pure sample to higher values (3.14 ± 0.06 eV) for doped samples due to the quantum confinement effect. These results agreed with the DC conductivity of samples. The ionic conductivity σ_ionic was developed with dual doping. The characterization of the doped samples makes them good candidates for photoelectronic applications.

Enhanced electrochemical performance of facilely synthesized cobalt doped cubic NiO nanoflakes for supercapacitor application

Being inexpensive, nontoxic and environmental friendly, NiO has caught special attention as a promising electrode material for supercapacitors. We recently reported facile synthesis of porous NiO nanocrystallites for energy storage application. A sophisticated strategy to improve the electrochemical properties of NiO which is a p-type semiconductor is the incorporation of 3d metal ions into it. In this article, we present successful fabrication of highly porous cobalt doped NiO nanostructures through a facile, low cost, one step solution combustion method without a post calcination treatment and demonstrate the influence of cobalt content on structural properties and electrochemical behavior. The thus prepared Co doped NiO samples were systematically characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Field emission scanning electron microscopy, High resolution transmission electron microscopy, X-ray photoelectron spectroscopy, Brunauer-Emmett-Teller measurements, cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy. It was found that the phase structure of pristine NiO remains unaffected by the process of doping. But doping obviously influences the textural and morphological properties, more importantly, enhances the electrochemical properties of pristine NiO. A maximum specific capacity of 746 C/g (specific capacitance of 1244 F/g) was obtained for an optimum cobalt dopant ratio, which is superior to undoped NiO (295 C/g). Moreover, cobalt doped NiO nanostructures exhibited a good rate capability (71 % capacity retention from 1 to 15 A/g) and long term cycling stability (83.7 % after 5000 cycles at 100 mV/s). An asymmetric device fabricated using Co doped NiO electrode as the positive electrode and activated carbon as the negative electrode delivered an energy density of 32.7 Wh/kg at a power density of 261 W/kg.

Methanol sensing using Zn doped NiO nanoparticles

In the present study, we report gas sensing properties of Zinc doped nickel oxide nanoparticles. The Zn doped NiO samples were successfully synthesized by chemical co-precipitation method at room-temperature. Raman studies revealed the presence of defects such as nickel vacancies, which encourage the better sensing results. These defects are essential for providing active sites for adsorption of gaseous molecules and assists in improving the sensing parameters. Further, the sensor response of device has been found to be 7.2 when exposed to 100 ppm of methanol at 260 °C. Obtained Zn doped NiO sensor was found to be selective towards methanol as compared to other volatile compounds including, ethanol, acetone, ammonia and hydrogen.

Fabrication and study of self-assembled NiO surface networks assisted by Sn doping

Complex patterning of surfaces commonly requires a significant effort in terms of time, cost, and advanced post-fabrication treatments design, which could be overcome by self-organization mechanisms avoiding damage to the surface materials and enhancing properties of interest. In the present work, grid self-assembled NiO complex surfaces have been fabricated assisted by Sn incorporation during growth, following thermal treatments at 1400 °C under a controlled Ar flow. The singular morphologies achieved enable the fabrication of robust high surface to volume ratio surfaces with a wide range of surface properties and functionalities. Based on the research performed by a set of complementary techniques, the mechanisms involved in the formation of these textured surfaces have been discussed and some of the fundamental electronic and optical properties of NiO have been analyzed, both aspects necessary to head up the potential development of applications based on this p-type material which is arousing growing attention. These singular micro- and nanostructures present high luminescence and tunable performance unusual to bulk NiO samples, which can broaden the applicability of this material to light-emitting devices. Moreover, the surface evolution depends on a controllable way on the preferential state of charge of the incorporated Sn, which could be selected through the convenient Sn-based precursor, its ratio to the metallic Ni starting precursor, and the atmosphere and duration of the fabrication treatment. Finally, in order to assess the dependence of some potential NiO-based applications on the insights achieved on the surface characterization, the gas-sensing response to ethanol from the Sn doped NiO samples was also evaluated. The study of the processes and mechanisms involved in the growth of these grid-patterned surfaces can be extended to similar oxide-based systems.

Dielectric relaxation and Hopping conduction mechanism in Ni1-xSrxO nanostructures

Electrical transport and conduction characteristics of sol-gel prepared Ni1-xSrxO (x = 0.00, 0.02, 0.04) nanostructures have been investigated systematically through DC and AC conduction measurements. The phase purity and structure of the samples have been studied using X-ray diffraction refinement and transmission electron microscope (TEM) analysis. It is observed that metal to semiconductor transition takes place in pure NiO sample whereas, it is suppressed on Sr insertion into NiO lattice. The activation energy (Ea) of the DC conduction have been found between 0.18 and 0.49 meV. Further, we have also observed relaxation process in doped NiO samples which are established by peaking behavior of dielectric constant. To discuss the conduction mechanism, the AC conductivity and temperature dependence of frequency exponent ‘n’ have been analysed using quantum mechanical tunnelling based Non-Overlapping Small Polaron (NSPT) model. Simultaneously, correlated AC conductivity data with NSPT model was used to calculate the value of maximum barrier height (binding energy) (Wm), AC activation energy, tunnelling distance (Rw) and density of states at Fermi level N (EF). Also, impedance spectroscopy suggests that the pure and Sr doped samples exhibit high order insulating behavior at the temperatures of 30 °C and 150 °C.

Enhanced optical properties of pure and Sr doped NiO nanostructures: A comprehensive study

We have discussed the detailed optical properties of Ni1-xSrxO (x = 0.0, 0.02, 0.04) nanoparticles calcined at 700 °C which have been synthesized using liquid-solid phase route such as sol-gel method. To discuss the optical behavior, we focus on the reflectance/transmittance spectra of pure and Sr doped NiO samples. Here, we found low reflectance about 15% and high transmittance 41.48% in the visible region which more confirm the high transparency in the visible region. The refractive index n (λ) and extinction coefficient k (λ) spectra of our samples show normal and anomalous dispersion in the range 200–800 nm. In addition, optical dielectric constants, optical conductivity (σ), high frequency dielectric constant using dispersion through both of free carriers and bound carriers, static refractive index (no), Wemple Di-Domenico (WDD) static refractive index (noWDD), ratio of free carrier concentration, effective mass ( Nm*) and plasma frequency (ωp) have been determined. The refractive index dispersive behavior is also examined through WDD single oscillator model and optical dispersion parameters Eo and Ed were calculated using WDD model. Simultaneoulsy, through deconvoluted PL spectra using Gaussian function for all the samples, we found extra green and yellow bands are originate in PL emission spectrum for pure NiO sample and further these bands supressed in Sr doped NiO samples which confirm the reduced defects in the NiO on the Sr doping.

Structural, morphological, optical and third order nonlinear optical response of spin-coated NiO thin films: An effect of N doping

The present work deals with the deposition of NiO and Nitrogen (N)-doped NiO thin films by sol-gel spin coating technique. Structural, morphological, linear and non-linear optical characteristics of undoped and N-doped (1–15 wt%) NiO films were studied. From XRD measurements, it is evident that single phase nano crystalline NiO is formed for all doping concentrations. Surface morphology study shows that higher concentration of N doped NiO thin films were of high quality and EDX mapping confirmed the doping of Nitrogen in films. The Raman spectra of the studied films were analyzed over the range of 1400-200 cm−1. The optical studies confirm that as doping increases, transparency of the film decreases (except at 10% N doping) and the band gap narrows. Nonlinear parameters such as refractive index and susceptibilities also depend on N dopant concentration. Z-scan studies viz., absorption index, nonlinear refractive index were carried out on undoped and N doped NiO samples and the results were matched with theoretical calculated values.

Structure and room-temperature ferromagnetism evolution of Sn and Mn-doped NiO synthesized by a sol-gel process

Abstract The development of room temperature ferromagnetism is imperative for energy systems such as data storage in computers and spintronics. Herein we report a room temperature ferromagnetic study of Sn and Mn doped nickel oxide synthesized by sol gel method. The size and morphology of the samples are calculated using XRD and TEM analysis. The XRD and Fourier transform infrared (FTIR) results indicate that the synthesized NiO powders have a pure cubic structure. The variation in lattice parameters has been studied using the Rietveld refinement of X-ray diffraction pattern. The addition of dopants does not affect the structure of NiO. The presence of dopants in the doped NiO samples has been confirmed with Energy Dispersive Spectroscopy (EDS) analysis. The Photoluminescence (PL) spectrum shows enhanced luminescence intensity for Sn doped NiO than Mn doped NiO. The magnetic properties of the samples have been studied using Vibrating sample magnetometry (VSM). The pure and Mn doped NiO samples are found to exhibit ferromagnetism. The Sn doped NiO samples exhibit superparamagnetism making them suitable for applications in ferrofluids and as contrast agents for magnetic resonance imaging. The coercivity and magnetization of the Mn doped NiO samples are found to be enhanced compared to the pure NiO. The Sn doped NiO samples have very low value of coercivity compared with both pure and Mn doped NiO samples. The observed room temperature ferromagnetism in doped NiO makes it a suitable candidate for DMS devices such as MR imaging and magnetic delivery.

Effect of calcination temperature on Cu doped NiO nanoparticles prepared via wet-chemical method: Structural, optical and morphological studies

In the present study, NiO and Cu-doped NiO nanoparticles were successfully synthesized by wet chemical method at room temperature using sodium hydroxide (NaOH) as precipitating agent. The as-prepared Cu-doped NiO powder samples were subjected to three different calcination temperatures such as, 350°C, 450°C and 550°C in order to investigate the impact of calcined temperatures on the phase formation, particle size and band gap evolution. The phase formation and crystal structure information of the prepared nanomaterials were examined by X-ray powder diffraction (XRD). XRD revealed the face-centered cubic (FCC) structure. Average crystalline size of pure and doped samples estimated using Scherer formula was found to be 15nm and 9nm respectively. With increase in the calcination temperature from 350°C to 550°C for the Cu doped NiO samples the particle size of the nanoparticles was found to increase from 4nm to 9nm respectively. The optical study for both pure and doped NiO nanoparticles was performed using an UV–Vis spectrophotometer in the wavelength range of 200–800nm. The strong absorption in the UV region confirms the band gap absorption in NiO and was estimated from the UV–Vis diffuse reflectance spectra via Tauc plot. Systematic studies were also carried out to study the effect of calcination on the optical transmittance. Samples were also investigated using Raman and Fourier Transform Infrared Spectroscopy (FTIR). Furthermore, morphology of the pure NiO and Cu-doped NiO Nanoparticles were examined by scanning electron microscope (SEM).

Synthesis, structural, Raman spectroscopic and paramagnetic properties of Sn doped NiO nanoparticles

In this work, Sn doped NiO nanoparticles were synthesized by co-precipitation route to explore the impact of doping on lattice structure, dielectric constant and magnetization. X-ray diffraction analysis confirmed cubic (Fd-3m) structure of all as prepared Sn doped NiO samples. Average crystallite size decreases from 78.2nm (Ni0.95Sn0.05O) to 64.23nm (Ni0.8Sn0.2O). Scanning electron microscopy images confirm that nanocrystals have agglomerated spherical morphology. The Fourier transform infrared spectroscopic analysis, the spectral absorption bands at about 460cm–1 corresponds to metal oxygen bonding. This band is red shifted on enhanced doping of Sn in NiO. Comparing with bulk NiO, the Sn doped NiO samples showed a blue shift. The dielectric constants at about 1Hz are measured to be about 1.795, 1.030, 0.442, and 0.302×103 for Ni1−xSnxO (x=0.05, 0.1, 0.15, 0.2), respectively. The dielectric constant in nanoparticles of doped Ni1−xSnxO is three orders of magnitude higher as compared to pure NiO ceramics. The nature of magnetization – applied field (M–H) infers paramagnetic behaviour for Sn doped NiO nanoparticles.

Study of Magnetic and Electrical Properties of Nanocrystalline Mn Doped NiO

Diluted Magnetic Semiconductors (DMS) are intensively explored in recent years for its applications in spintronics, which is expected to revolutionize the present day information technology. Nanocrystalline Mn doped NiO samples were prepared using chemical co-precipitation method with an aim to realize room temperature ferromagnetism. Phase formation of the samples was studied using X-ray diffraction-Rietveld analysis. Scanning electron microscopy and Energy dispersive X-ray analysis results reveal the nanocrystalline nature of the samples, agglomeration of the particles, considerable particle size distribution and the near stoichiometry. Thermomagnetic curves confirm the single-phase formation of the samples up to 1% doping of Mn. Vibrating Sample Magnetometer measurements indicate the absence of ferromagnetism at room temperature. This may be due to the low concentration of Mn2+ ions having weak indirect coupling with Ni2+ ions. The lack of free carriers is also expected to be the reason for the absence of ferromagnetism, which is in agreement with the results of resistivity measurements using impedance spectroscopy. Arrhenius plot shows the presence of two thermally activated regions and the activation energy for the nanocrystalline Mn doped sample was found to be greater than that of undoped NiO. This is attributed to the doping effect of Mn. However, the dielectric constant of the samples was found to be of the same order of magnitude very much comparable with that of undoped NiO.

Comparative structural and electrical analysis of NiO and Ti doped NiO as materials for resistance random access memory

In order to investigate the mechanism behind bistable resistance switching in NiO thin films, we have done detailed x-ray photon spectroscopy (XPS) and x-ray diffraction Analysis (XRD) on NiO and Ti doped NiO samples fabricated under various conditions. We discovered that a high initial resistivity was required for samples to undergo bistable resistance switching, and the presence of metallic Ni content in these samples was determined by XPS. XRD data also showed that NiO grown with a relative (200) orientation was preferred over those grown with relative (111) orientation.

Analysis of AC electrical properties of (Li and Ti)-doped NiO

(Li and Ti)-doped NiO samples were prepared by the citrate precursor method followed by a sintered process, and impedance spectroscopy (IS) of these samples was measured as a function of frequency and temperature. Accordingly, the impedance spectra exhibit two depressed semicircles when the Ti content is more than 5 mol.%, which is corresponding to the core–shell microstructure. The simple resistor–capacitor (RC) effective circuit and the modified effective circuit (the capacitor in the RC circuit is replaced by a constant-phase element (CPE)) were used to fit the experimental data. And it is indicated that the CPE element is an effective tool to analyze IS.

Surface and Catalytic Properties of NiO and Co3O4 Solids Doped with Cobalt and Nickel Ions

The effects of doping NiO and Co3O4 solids with cobalt and nickel species on their surface and catalytic properties were investigated. The amounts of dopant, in the form of the corresponding nitrate, were varied between 0.5–6.0 mol% cobalt ions and 2.0–6.0 mol% nickel ions. Pure and variously doped solids were subjected to thermal treatment at 300–700°C. The techniques employed were XRD, nitrogen adsorption at −196°C, decomposition of H2O2 at 30–50°C and estimation of the amount of surface excess oxygen on the variously prepared solids as determined by the hydrazine method. The results obtained revealed that the pure and variously doped NiO samples precalcined at 300°C consisted of a finely divided NiO phase having an average particle size of ca. 40 Å. Pure and variously doped Co3O4 specimens preheated at 500°C and 700°C were composed of a Co3O4 phase with a much bigger particle size (230 Å and 350 Å, respectively, for the solids precalcined at 500°C and 700°C). Doping of NiO followed by thermal treatment at 300°C and 500°C resulted in a measurable decrease in its BET surface area (19–23%), while doping of Co3O4 with nickel species followed by heating at 500°C and 700°C brought about a significant increase in its specific surface area (56–60%). Doping each of the NiO and Co3O4 solids with cobalt and nickel species greatly increased the amount of surface excess oxygen and effected a considerable increase in their catalytic activities. This increase was, however, much more pronounced in the case of NiO which attained a value of ca. 100-fold. Doping of NiO with cobalt species followed by thermal treatment at 300°C and 500°C decreased the activation energy (DE) of the catalyzed reaction to an extent proportional to the amount of dopant added. On the other hand, doping of Co3O4 with nickel species followed by thermal treatment at 500°C and 700°C did not change the value of DE. These results suggest that doping of Co3O4 with nickel species did not modify the mechanism of the catalyzed reaction but increased the concentration of catalytically active sites without changing their energetic nature.

Effects of doping on the electrical properties and surface characteristics of NiO catalyst

A series of nickel oxides doped with 10 at.% Li, 20 at.% Na and 10 at.% Fe was prepared by thermal dehydration of mixed hydroxides in air at temperatures in the range 300–1000 °C. The electrical properties, stoichiometric composition and surface characteristics of the pure and doped NiO samples were investigated. Alkali doping considerably increased the electrical conductivity and decreased the specific surface area of NiO. The modifications in the electrical and surface properties were more pronounced, however, in the case of lithium doping. In contrast, doping with Fe 2O 3 produced opposite effects on the electrical and surface properties of NiO. Lithium doping was accompanied by pore narrowing when the preparation temperature exceeded 500 °C. A less important pore narrowing was observed in the case of sodium doping at temperatures above 700 °C. At 300 °C the doping of NiO with foreign ions might proceed through coverage of a fraction of the NiO surface by some of these ions. Above 400 °C foreign ions could progressively substitute some of the lattice nickel ions according to the mechanism of Verwey and de Boer. Above 600 °C Fe 3+ ions could be incorporated in the NiO lattice according to another mechanism.