Research Journal of Chemical Sciences ______________________________________________ ISSN 2231-606X Vol. 2(8), 37-42, August (2012) Res.J.Chem.Sci. International Science Congress Association 37 Synthesis and Characterisation of Nano crystalline Neodymium Nickelate (NdNiO) Powders using Low Temperature Molten Salt Technique Ignatius Arockiam S., Peter Pascal Regis A. and John Berchmans L.Department of Chemistry, St. Joseph’s College, Tiruchirappalli - 620 002, Tamil Nadu, INDIA Electropyrometallurgy Division, CSIR-Central Electrochemical Research Institute, Karaikudi-630 006, Tamil Nadu, INDIAAvailable online at: www.isca.in Received 19th April 2012, revised 30th April 2012, accepted 25th April 2012Abstract The ultrafine neodymium nickelate (NdNiO) powders have been prepared by molten flux method using oxide precursors. The synthesized materials were characterised using XRD, FTIR, CHNS, EDAX and EPR analytical techniques. The morphology of the synthesized crystals were scrutinized using scanning electron microscopy (SEM). The XRD analysis has shown that the synthesized crystal has possessed cubic structure. FTIR spectrum exhibits the absorption bands for the Nd-O stretching vibration and Ni-O bands at different wave lengths. The CHNS analysis presents the impurities level in the synthesized compound. EDAX analysis gives the concentration of Nd, Ni and O ions in the compound. The lone pair of electron state is identified from the EPR spectrum. The SEM micrographs depicts the presence of fine crystallites with assorted morphology. The average particle size of the powders is ranging between 25-35 m. From the above studies, it has been concluded that pure crystals of NdNiO3 compound can be synthesized by low temperature molten salt technique. Keywords: Molten salt synthesis, neodymium nickelate, XRD, FTIR, SEM. Introduction Perovskite ABO3 materials are of worldwide interest because of their very interesting properties, such as ferroelectric, magnetic, optical and colossal magnetoresistance, high-Tc superconductivity, non-volatile memory effectsThermoelectric devices have been used in broad areas such as refrigerators and in cooling units for fiber junctions in optical fiber communication technology Their crystal structure consists of corner sharing BO6 octahedra with the A ion in a high co-ordination site. The relative ionic radii of Am+ or Bn+ (m+n = 6) give rise to ‘distorted’ perovskite structures with cubic symmetry. Tungsten trioxide exhibits a cubic perovskite like structure based on the corner sharing of regular octahedra with the oxygen atoms at the corner and the tungsten atoms at the center of each octahedron. A variety of transition and non transition metal ions can be substituted either fully or partially in A and B sites. This gives rise to an extraordinary range of phenomena such as ferroelectricity, superconductivity, high temperature ionic conductivity, a variety of magnetic ordering etc. In recent years cerium-based catalysts have been investigated since they find potential applications for the treatment of exhaust gas from automobiles to their use in methanol formation7,8 the water gas shift reaction9,10 acetone hydrogenation, alkadiene hydrogenation11 and catalytic oxidation of CO12 and of light hydrocarbons13-15 CdS thin films have been prepared by diverse techniques: sputtering, vacuum evaporation, spray pyrolysis, electrodeposition and chemical bath deposition (CBD)16 Copper selenide is an interesting metal chalcogenide semiconductor material. It has a number of applications in solar cells, super ionic conductors and photo-detectors17 Nanosized metal oxide particles can be synthesised by a variety of methods, including chemical gas phase growth methods such as chemical vapor deposition (CVD), sol-gel processing and reverse micelle18 laser pyrolysis19 self-assembly templating20, electrochemical synthesis21 metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxial, and plasma synthesis22,23. Photodegradation of phenol in presence of UV light using semiconductor metal oxides (such as ZnO, SnO, Fe, CdO, TiO etc) is an efficient technique in wastewater treatment24. Molten salt synthesis is one of the most versatile techniques to prepare highly ordered complex oxide materials. The molten salts are used as the reaction medium for the reactants dissolution and product precipitation. Studies have shown that the products obtained from molten salts are influenced by the synthesis conditions, such as the type of salt used, the annealing temperature, the temperature ramp rate, the precursor composition and the solubility of the reactive constituents in the molten salt etc25-27. The molten salts rendered homogeneous distribution and high intimacy of the reactive components at the atomic scale in the initial mixture of precursor salts. Hence, the diffusion distance and the rate of the reactive species in molten melts are modified and an efficient material transport is enabled to meet the minimal kinetic requirement for the reaction28-30. Generally the starting materials for molten salt synthesis are inorganic compounds such as sulfates, chlorides and oxides, which are Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(8), 37-42, August (2012) Res.J.Chem.SciInternational Science Congress Association 38 blended with the alkali metal nitrates, chlorides, carbonates, hydroxides as a powder mixture before heating to the reaction temperature. Many complex oxide materials have been synthesized by molten salt technique 31-34. Even though, many soft chemical routes have been attempted, only few studies have been made on the synthesis of NdNiO3 compounds using molten flux method. Hence, an attempt has been made on the preparation of NdNiO by this method. Material and MethodsReagent-grade chemicals like neodymium oxide (Nd), nickel oxide (NiO) were used as the starting materials. They were obtained from Merck India Ltd, Bombay. Appropriate amount of chloride salts such as sodium chloride (NaCl) and potassium chloride (KCl) were used as the flux. They were thoroughly ground using a mortar and pestle and were placed in a high density alumina crucible. The mixture was then heated in an electrical resistance furnace at 900C for 12 hrs. The heating rate was 200°C per hour for all the experiments.The resulting reaction mixture was cooled to ambient temperature. The contents were removed from the crucible and washed with hot water for several times. The unreacted neodymium, nickel, alkaline salts were removed by treating with these solvents. The residual powders were dried in a vacuum oven at 50°C for 1 hour and cooled to room temperature. The method of synthesis is presented in the form of a flow chart and shown in figure 1. Finally free flowing black powders were obtained and they were characterized for their physicochemical properties. The purified powders were characterized by XRD (Philips 8030 X-ray diffractometer) to identify the phase purity of the compound. The unit cell lattice parameters were obtained by the Least-square fitting method of the d-spacing and the hkl values. Fourier transform infrared (FTIR) spectroscopy was used to study the structure coordination of the calcined powders using Perkin Elmer UK paragon-500 spectrophotometer. To record the spectrum, each sample was mixed with KBr, ground in to fine powder and made into pellet. It was then examined in the wave number ranging from 400-4000 cm 1. Carbon, hydrogen, nitrogen, and sulphur contents of the samples were assessed using an elemental analyzer Vario EL III-Germany Instrument. Electron spin resonance (ESR) spectroscopical analysis was performed using microwave frequency 9.857403 GHz with fields corresponding to about ~ 6500.000G sweep width using a Bruker Bio Spin Gmbh EPR spectrometer. The morphology of the synthesized powders was examined by a Scanning Electron Microscope (SEM)-JSM-3.5 CF, Japan JEOL make. Figure -1 Flow chart for the preparation of NdNiO compound Nd NaCl/KCl Flux Thermal treatment at 900 0 C Mixed and placed in Alumina crucible NiO Washing with hot water Fine crystalline NdNiO Dyring in hot air oven Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(8), 37-42, August (2012) Res.J.Chem.SciInternational Science Congress Association 39 Results and DiscussionThe XRD data of the synthesized crystals are presented in figure 2. The lattice constant values are determined using the equation, 1/d= h/a +k/b +l/cFigure-2 X-ray diffraction spectrum of NdNiOAll the XRD peaks are indexed assuming a orthorhombic structure. The calculated lattice parameter values are in good agreement with the reported values. The d spacing values of calcined powders are well matched with the XRD pattern of NdNiO3. The average crystallite size of the products was determined from the XRD patterns according to the Scherrer’s equation D = 0.9 / cos. The average crystallite size is ranging between 85-100nm. Fourier transform infrared (FTIR) spectroscopical analysis: FTIR spectrum recorded for the neodymium nickelate compound and presented in figure 3. The transmittance band appeared at 3462 cm-1 may be attributed to the O-H stretching vibration of water molecules as reported in the literature35. The bands seen between 1364 to 1707 cm-1 are related to the coordination of the Ni3+cations as reported by Fernades et al.36. The transmittance bands in the wave length region of 3434-3404 cm-1 are responsible for the formation of the single phase NdNiOcompound. The bands noticed at higher wavelength region may be assigned to the Ni-O bands. Figure-3 FTIR spectrum of NdNiO compound Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(8), 37-42, August (2012) Res.J.Chem.SciInternational Science Congress Association 40 Carbon, hydrogen, nitrogen and sulfur (CHNS) analysis: The results on the CHNS analysis are presented in table 1. From the table, it is noticed that the compound has associated with some minor impurities such as C, H and S. Table -1 Chemical analysis of the compound of NdNiOCompound C (%) H (%) N (%) S (%) NdNiO 3 0.167 0.035 0.000 0.067 Energy dispersive X-ray analysis (EDAX): The elemental analysis of the synthesized compound was performed using energy dispersive x-ray analysis technique. Figure 4 represents the EDAX profile of Nd, Ni and O of the synthesized NdNiOcompound. The results on the EDAX analysis are presented in Table.2. The spectrum exhibits the constituent elements are in appropriate weight percentage. Table-2 EDAX analysis data Compound Nd (wt%) Ni (wt%) O (wt%) NdNiO 3 57.84 32.04 10.12 Electro paramagnetic resonance (EPR) studies: The paramagnetic resonance spectrum of the NdNiO is presented in figure 5. From the EPR spectrum, it is noticed that the value of g factor is g=2, which represents the paramagnetic entities present in the parent compound. The lone pair electron state is identified from the spectrum. It is also revealed that the position of the signal is very close to the value expected for uncorrelated spins with the gyromagnetic factor Nd3+ Ni2+ dipolar interactions. Ultra-violet spectroscopic studies: Figure 6 shows the UV-Visible spectrum of the synthesized NdNiO3 compound. A broad absorption band is noticed at 340 nm in the spectrum represents the Ni-O and Nd-O absorption bands. From the spectrum, the band gap of the material is determined using the formula E = h and found to be 5.84 eV. SEM analysis: The morphological features of the synthesised powders were obtained by means of scanning electron microscopy. Figure 7(a) and 7(b) show the scanning electron micrographs of NdNiO3 compound obtained by molten salt Synthesis (MSS) route. The crystals have shown an assorted plate like particle morphology. The average particle size of the powders is ranging between 25-35 m. Figure-4 EDAX profile of Nd, Ni, and O in NdNiO3 Figure-5 Figure-6 EPR spectrum of NdNiOcompound UV-Visible spectrum of NdNiO compound Research Journal of Chemical Sciences __________________________________________________________ ISSN 2231-606X Vol. 2(8), 37-42, August (2012) Res.J.Chem.SciInternational Science Congress Association 41 (a) (b) Figure-7 (a) and (b) SEM image of NdNiO3 ConclusionFine crystalline NdNiO powders are successfully synthesized using low temperature molten salt technique. The XRD analysis confirms that the compound has the cubic structure. 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