Abstract
A solid-state reaction technique was used to synthesize polycrystalline Na2WO4. Preliminary X-ray studies revealed that the compound has a cubic structure at room temperature. The formation of the compound has been confirmed by X-ray powder diffraction studies and Raman spectroscopy. Electrical and dielectric properties of the compound have been studied using complex impedance spectroscopy in the frequency range 209 Hz–1 MHz and temperature range 586–679 K. The impedance data were modellized by an equivalent circuit consisting of series of a combination of grains and grains boundary. We use complex electrical modulus M* at various temperatures to analyse dielectric data. The modulus plots are characterized by the presence of two relaxation peaks thermally activated. The morphologies and the average particle size of the resultant sodium tungstate sample were demonstrated by atomic force microscopy, scanning electron microscopy and transmission electron microscopy. The thicknesses and optical constants of the sample have been calculated using ellipsometric measurements in the range of 200–22 000 nm by means of new amorphous dispersion formula which is the objective of the present work. The results were obtained for Na2WO4 particles from experimental (EXP) and measured (FIT) data showed an excellent agreement. In addition, the energy gap of the Na2WO4 sample has been determined using ellipsometry and confirmed by spectrophotometry measurements.
Highlights
The tungsten compounds of general formula AWO4 and B2WO4 (A, divalent cation; B, monovalent cation) crystallize following two structural types whose nature depend on the ionic radius of the cation element (A or B)
The room temperature X-ray diffraction (XRD) pattern is shown in figure 1
Electric modulus formalism is an important theory. It has been used in the analysis of the electrical properties because it gives the main response of the bulk of the crystal sample and is suitable to extract phenomena, and it permits us to study charge transport processes in ion conductors and eliminates the electrode polarization effect [24]
Summary
The tungsten compounds of general formula AWO4 and B2WO4 (A, divalent cation; B, monovalent cation) crystallize following two structural types whose nature depend on the ionic radius of the cation element (A or B). Sodium tungstate (Na2WO4) and sodium molybdate (Na2MoO4) crystals are isostructural, and they belong to the class of spinel crystals with general formula Na2XnO3n+1 (X = W, Mo) [2,3]. Sodium tungstate is used as a catalyst for epoxidation of alkenes and oxidation of alcohols into aldehydes or ketones It is known for its anti-diabetic effects; researchers have identified the pathways through which sodium tungstate improves pancreatic function and β cell proliferation [6]. These kinds of samples Na2XnO3n+1 have been studied for a long time in order to understand the physical and chemical behaviour, such as structure, phase transition and vibrational investigation [7,8]. The results show for the first time, to our knowledge, the optical properties of the Na2WO4 sample using spectroscopic ellipsometry (SE) in the range of 200–2200 nm with a step of 1 nm by means of the DELTA PSI2 software based on a new amorphous dispersion formula at room temperature
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