Abstract
The microwave-assisted hydrothermal method was used to obtain α-Ag2WO4. Rietveld refinement confirmed that α-Ag2WO4 is stable in the orthorhombic phase, without secondary phase. However, field-effect scanning electron microscope analysis showed that α-Ag2WO4 nanorods surfaces contain silver nanoparticles, confirmed by the X-ray photoelectron spectroscopy by the peak observed at 374.39 eV. In addition to metallic Ag, other Ag oxidation states were also observed on the surface. Hence, Ag (I) as Ag2O and Ag (I) as Ag2WO4 also were identified. DC measurements exhibited a high capacity of charge storage, nevertheless, with a large loss tangent (0.12 µC.cm-2.V-1) and no residual polarization for the voltage range between -100 V and +100 V. AC measurements at frequencies less than 275 Hz, revealed that ionic polarization is dominant, whereas at frequencies higher than 275 Hz, the electronic behavior predominates. The potential of electromagnetic energy conversion in thermal was observed from loss tangent analysis.
Highlights
Tungsten-silver materials are known to exhibit very good erosion resistance properties in low voltage
The good overlap between experimental and standard profiles and the values of the statistical parameters Rwp, Rexp, and Goodfitness (ꭓ2) shown in Table 1 confirm the good quality of the refinement from the Rietveld method, since they are in agreement with values reported in literature 15,22-24 for the α-Ag2WO4 structure
Confirming this behavior, recent studies reported that cluster units formed by [WO6] and AgOy (y = 2, 4, 6, and 7) display a degree of distortion at short, medium, and longrange generated by changes in bond angles and lengths, which vary for different synthesis methods, leading to changes in the physical and chemical properties such as photoluminescence, 22-24 bacterial activity[24,29,44], and gas sensing[26,42]
Summary
Tungsten-silver materials are known to exhibit very good erosion resistance properties in low voltage Their use as arcing contacts in circuit breakers is limited when exposed to harsh working environments because of the ease with which they form oxides on the surface, thereby leading to increased contact resistance 1-5. The thermodynamic instability of tungsten-silver materials reduces their usefulness at high temperatures near electric arcing regions[1,6], because this might result in the formation of different phases with distinct physical and chemical properties, such as silver tungstates (Ag2WO4 and AgWO3)[6], silver oxide (AgO2)[7] and tungsten oxides (WOx)[4,6,7,8], which would degrade the circuit breaker performance[1,6]. In this work we concentrate on the structural and microstructural analysis of α-Ag2WO4 , that were crucial for a better understanding of its structural stability and AC/DC electrical properties witch show up an interesting potential as electrothermal energy conversion
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