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 × 103 switching cycles and maintained a stable polarization value of 0.058 μC/cm2 under 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 Bi3Mn2O7 nanocrystals might be suitable as nanocapacitors toward energy storage application.