Dielectric Stabilization and Loss Suppression in LDPE-Bi₂Te₃ Composites via Al₂O₃-Coated Aluminum Fillers

This study investigates the dielectric properties of low-density polyethylene (LDPE)-based composite materials containing semiconducting Bi₂Te₃ and Al₂O₃-coated aluminum particles over the temperature range 20–140 °C at a constant frequency of 1 kHz. Composites containing 3 and 5 vol.% Bi₂Te₃, as well as hybrid systems incorporating Al₂O₃-coated aluminum particles (LDPE + 3% Bi₂Te₃ + 7% Al₂O₃-coated Al and LDPE + 5% Bi₂Te₃ + 5% Al₂O₃-coated Al), were analyzed. The dependencies of the dielectric permittivity (ε′) and dielectric loss tangent (tan δ) on temperature show the presence of significant stabilization of the dielectric properties, suppression of loss processes, and a decrease in temperature-induced conductivity due to the addition of Al₂O₃-coated aluminum particles. In particular, the addition of Al₂O₃-coated aluminum particles resulted in a reduction of the dielectric loss tangent by about 60–75% relative to the LDPE-Bi₂Te₃ composites containing uncoated particles, while maintaining nearly the same dielectric permittivity values. The achieved results prove that Al₂O₃ coating serves as an effective insulation layer and charge stabilization phase for LDPE-Bi₂Te₃ composites, whereas the aluminum core contributes to the enhancement of local polarization effects.