Oxygen Vacancy-Controlled Dielectric Relaxation and Field-Driven Polarization of Bismuth-Manganese Bimetallic Oxide Nanoparticles: Implications for Capacitors

The synthesis of organic molecule-stabilized orthorhombic bismuth-manganese bimetallic oxide (Bi₃Mn₂O₇) nanocrystals is reported using a single-pot, chemical complexation route. Oxygen vacancy-related dielectric relaxation, electrical conductivity, and field-driven polarization have been investigated in wide-range temperature and frequency conditions. The improved capacitive performance with increasing temperature was correlated to the thermally activated formation of space-charge in the nanocrystal via a Mn-O network with a maximum value of the dielectric constant (ε′) of ∼840 at 140 °C. A reduction of relaxation time under a DC bias revealed that the charge carriers are partially confined into the localized potential states. Under an electric field condition, the fatigue-free polarization hysteresis loop was achieved in the materials for 5 × 10³switching cycles and maintained a stable polarization value of 0.058 μC/cm²under an electric field of 10 kV/mm. The slim polarization hysteresis and stable endurance performance in the presence of a high electric field suggested that Bi₃Mn₂O₇nanocrystals might be suitable as nanocapacitors toward energy storage application.