F. Soofivand
National Research Council-Nanoscience Institute (CNR-NANO) and NEST-Scuola Normale Superiore, Piazza S. Silvestro 12, 56127 Pisa, Italy,
Italy
Keywords: smart materials, nanocomposite, graphene, thermochromism, superionic solid electrolyte, X2HgI4 (Tl, Cu)
Summary:
This study investigates the synthesis and characterization of X₂HgI₄ (X = Tl, Cu) graphene-based nanocomposites, focusing on their enhanced thermochromic and superionic properties. These materials demonstrate exceptional thermochromic behavior, undergoing a phase transition with a visible color change, making them promising candidates for smart materials used in temperature-sensitive applications such as sensors and display technologies. The introduction of graphene into the X₂HgI₄ matrix plays a critical role in modifying the phase transition temperature and optical properties of these materials. Graphene's high thermal conductivity reduces the phase transition temperature by efficiently dissipating heat, as confirmed by DSC analysis. This behavior is highly desirable for applications where rapid thermal responses are necessary. In addition, UV-vis spectroscopy reveals that graphene incorporation reduces the bandgap energy, improving optical absorption and making the composites suitable for photonic devices and optoelectronic systems. The X₂HgI₄ compounds also exhibit superionic conductivity, particularly in their high-temperature phases [1]. This behavior arises from the mobility of ions, such as Cu⁺ and Tl⁺, within the crystal lattice structure. Incorporating graphene enhances the ionic conductivity by providing additional pathways for ion migration, facilitated by graphene's high surface area and excellent conductivity. These improvements position the composites as viable candidates for solid electrolytes in energy storage applications, including solid-state batteries. Structural analysis using XRD confirmed the presence of the crystalline phases, ensuring the purity and stability of the synthesized nanocomposites. Additionally, SEM and TEM images illustrated the uniform dispersion of X₂HgI₄ nanoparticles across the graphene sheets. This uniform morphology minimizes agglomeration, improves thermal stability, and enhances the functional properties of the composites. In conclusion, X₂HgI₄ graphene-based nanocomposites demonstrate improved thermochromic, optical, and superionic properties, with graphene playing a pivotal role in optimizing their performance. The composites exhibit a lower phase transition temperature, superior optical absorption, and enhanced ionic conductivity, which are essential for advanced temperature-responsive sensors, photonic systems, and solid-state energy devices. These findings highlight the potential of X₂HgI₄ composites as next-generation smart thermochromic materials and efficient solid electrolytes for energy and sensor technologies. References: 1. F. Soofivand, M. Salavati-Niasari, Journal of Molecular Liquids 252, (2018), 112