Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) alloys – Optical and structural studies
Graphical abstract
Introduction
Researchers have huge interest in the preparation and characterization of ZnO semiconductor in nanoscale due to their peculiar properties such as wide band gap (3.4 eV), high excitonic binding energy (60 meV), high piezoelectric constant and environmental friendly characteristics [1], [2]. Recently, ZnO is found to be suitable material for solar energy conversion, storage device, spintronic devices, gas sensing, antibiotic, etc. [3], [4], [5].
Many physical properties such as optical, electrical conductivity, and magnetic are greatly influenced by type of impurity and its concentrations. Transition metal (TM) ion alters the electronic and magnetic properties of ZnO due to the exchange interaction between s and p electron of host ZnO and d electron of TM ions [6], [7]. Among different TM elements, Cu gets much interest due to its similar electronic shell structure, physical and chemical properties to those of Zn [8]. Singhal et al. found that the d.c. electrical resistivity of the ZnO decreased when Cu was doped with ZnO [9]. The doping dependent room temperature ferromagnetism was reported by Sharma et al. on Cu doped ZnO nanorods [10]. Photocatalytic activity and gas sensing activity of the ZnO nanoparticles were enhanced by Cu ion doping [11], [12]. Meanwhile the solubility of Cu in ZnO lattice was limited at 4 at% and the Cu doping beyond the solubility limit creates the metallic clusters [10]. The formation of metallic clusters leads to decrease in charge density of the materials [13]. The higher doping percentage without metallic cluster is ensured by the doping of two or more favour TM elements [14], [15]. Since Fe dopant have similar advantages like Cu dopant such as room temperature ferromagnetism, enhanced photocatalytic activity and gas sensitivity [16], [17], [18], Fe ion is selected as a second doping element. Therefore, in the present investigation Cu and Fe are co-doped with ZnO to ensure higher doping concentration without metallic cluster. The doping percentage of Cu and Fe is limited to 4 at% to avoid the metallic cluster formation. Among the different physical and chemical methods used to prepare the doped ZnO nanoparticles [15], [19], [20], [21], the sol–gel is used in the present investigation because it is one of the most important methods to prepare the nanoparticles in large scale with low coast.
Even though some of the research works have been carried out on Cu or Fe doped ZnO system separately [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], comprehensive study of the structural and optical properties of Cu and Fe co-doped ZnO nanoparticles is still scanty. Therefore, in present investigation, Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) nanoparticles were successfully synthesized by sol–gel method and the effect of Fe dopant on its structural, optical and morphological properties has been studied and discussed in detail.
Section snippets
Preparation of Zn0.96−xCu0.04FexO nanoparticles
The Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) nanoparticles were prepared by sol–gel method. High purity chemicals (Merc, >99% purity) such as zinc acetate dihydrate ((CH3COO)2Zn⋅2H2O), cupric acetate monohydrate ((CH3COO)2Cu·H2O) and iron (III) acetate tetrahydrate ((CH3COO)3Fe·4H2O) were used as precursors for the synthesis of Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) nanoparticles. Initially, appropriate amount of zinc acetate dihydrate was dissolved in N,N-Dimethyl formamide (C3H7NO) under constant stirring at
X-ray diffraction (XRD) – structural studies
The X-ray diffraction patterns of Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) nanoparticles are shown in Fig. 1a. All the diffraction peaks are very close to the standard data of hexagonal wurtzite structured pure ZnO (a = 3.2488 Å, c = 5.2061 Å, space group P63mc, 186, JCPDS data card No. 36-1451) with preferred orientation along (1 0 1) plane in all the samples. Similar diffraction pattern found in all Fe compositions reveals that the Fe ion doping does not affect the hexagonal wurtzite structure of ZnO. There are
Conclusions
Zn0.96−xCu0.04FexO (0 ⩽ x ⩽ 0.04) nanoparticles were successfully synthesized by sol–gel method. The hexagonal wurtzite structure of all prepared samples was confirmed by X-ray diffraction spectra. The Fe doping reduced the average crystal size by preventing subsequent growth of the grain surface and the morphology of the synthesized nanoparticles was analyzed and the nanosized particles were confirmed by scanning electron microscope images. The changes in d-value, cell parameters, volume, bond
Acknowledgments
The authors are thankful to the University Grant Commission (UGC), New Delhi, India, for financial support under the Project [File No.: 41-968/2012 (SR)].
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