Numerical studies on fluid flow using nanoparticles like Al₂O₃, TiO₂, and MoS₂ have been carried out in several academic publications. Still, the value of electrical conductivity used in these studies differ greatly. While some research consider these nanoparticles to be conductive and cause numerical modeling to be inconsistent, others perceive them as insulators. Correct simulations depend on a consistent supply of experimental or theoretical data on the electrical conductivity of these nanoparticles as a function of temperature. Could someone recommend books or research papers with thorough conductivity values for various nanoparticles?
Aluminum oxide is predominantly an insulator. Its electrical conductivity is quite low, primarily because it is an ionic compound with a wide band gap of about 8.8 eV. At ambient temperatures, its conductivity is negligible. However, when subjected to high temperatures, the ionic mobility increases slightly, which can enhance its conductivity. This effect is typically due to the increased vibration of lattice ions that can slightly be displaced from their positions, creating vacancies and allowing for minimal charge transport.
TiO₂ is a semiconductor with a band gap of approximately 3.2 eV for its rutile phase and 3.0 eV for the anatase phase, making it inactive for visible light without modification. Its conductivity increases with temperature due to increased carrier generation; thermal energy excites more electrons from the valence to the conduction band. Additionally, defects within the TiO₂ structure, such as oxygen vacancies, can act as charge carriers, enhancing conductivity as the temperature rises.
MoS₂ is a layered semiconductor with a band gap of about 1.2 eV to 1.8 eV depending on the number of layers (bulk to monolayer). It exhibits a transition from indirect to direct band gap as it moves to monolayer thickness. MoS₂’s conductivity is also temperature-dependent, where increasing temperatures increase intrinsic carrier concentration. At elevated temperatures, phonon scattering increases, which generally increases the mobility of charge carriers.
Summary For all three materials, the conductivity at different temperatures can be explained through their intrinsic electronic structure and how temperature influences phenomena such as carrier mobility, carrier concentration, and defect dynamics. These materials respond differently to temperature changes based on their crystal and electronic structures. As temperature increases:
- Al₂O₃ shows a minimal increase in conductivity due to ionic displacement.
- TiO₂ experiences enhanced conductivity primarily through increased electron-hole pair generation and defect-mediated transport.
- MoS₂ sees an enhancement in conductivity, particularly due to increased intrinsic carrier concentration and changes in electron mobility.
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