Investigating dielectric parameters of WO3/MoO3 nanocomposites with different structural phases of WO3 and MoO3 nanostructures

Abstract

The large-scale industrialization with the development of new technologies has exploited fossil fuel tremendously thereby becoming a threat to the energy sources in the future. The alternate energy resources are required so that desired amount of energy can be derived from them and stored when required. The high energy storage device including dielectric materials-based capacitors can play a crucial role in the fulfillment of the ever-increasing energy demand. The dielectric materials became an integral part of today’s electronics such as digital communication, electric hybrid vehicle, and portable electronic engineering, liquid crystal displays, dielectric resonator oscillator, etc. As gate dielectrics, transistor isolation structures, memory components, inter-level dielectrics, and charge storage in fast capacitors for power isolation, dielectrics play critical roles in integrated circuits. The performance requirements for these dielectrics are increasing considerably as the feature sizes of integrated circuits continue to shrink and speed rises. Even at package level power isolation capacitors, performance improvements are becoming increasingly challenging, necessitating the use of novel materials. As the industry approaches the nm generation, the problems for dielectric materials will become much more severe. Nanotechnology has the potential to offer novel nanostructured materials to meet these needs and therefore different types of metal oxide nanostructures and their nanocomposites have been employed for the dielectric properties and variation of different parameters. The effect of different parameters such as particle size, temperatures, morphology, and oxygen vacancies on the dielectric properties of polymers, metal oxide nanostructures, graphene-based materials, and nanocomposites has been studied. But the effect of different structural phases and morphologies on the dielectric properties of tunable transition metal oxide nanostructures is not so much explored. Various phases and morphologies have different atomic arrangements and shape structures. The transport of charge carriers is largely affected by these parameters on the field frequency. Therefore these parameters have to be explored for the transition metal oxide nanostructures.

Therefore, as-synthesized tungsten oxide (with two different orthorhombic WO₃.H₂O and monoclinic WO₃ phases), molybdenum oxide nanostructures (with three different phases such as hexagonal MoO₃, orthorhombic MoO₃, and mixed hexagonal-orthorhombic MoO₃), and their nanocomposites with different phase combinations were employed for the dielectric and ac conductivity analysis using impedance spectroscopy technique at room temperature. Various dielectric parameters such as dielectric constant, dielectric loss, loss tangent, complex impedance, and dielectric modulus have been estimated. It has been observed that the two phases affected the nanocomposites differently. Although the dielectric property of base materials MoO₃ was improved in nanocomposites using both phases, monoclinic WO₃ showed a synergistic effect and dielectric parameters such as dielectric constant shows higher values than both individual counterparts. The complex impedance analysis showed the effect of grain as well as grain boundary by showing the two semicircles using Nyquist plot analysis. Similarly, electrical conductivity analysis shows that ac conductivity was improved in nanocomposites but a large difference was observed in monoclinic-based nanocomposites. The conductivity was increased with applied field frequency from 20 Hz to1 MHz and obeys the universal Jonscher power law. The conductivity of the nanocomposites at a higher frequency and room temperature shows the order of 10^-4 which can further be improved with increasing temperature. Because of the vast variety of structural phases, morphology and good chemistry of tungsten and molybdenum atom can further be explored for energy storage devices.