Electronic Structure Design in High-Entropy Oxides: Enabling Frequency-Dependent Dielectric Behavior for Advanced Applications

This study investigates the design of an electronic structure in a defect-engineered (MgCoNiCuZn)O high-entropy oxide (HEO), demonstrating distinct frequency-dependent dielectric behavior enabled by a complex microstructure. Detailed structural analysis reveals a phase transformation from a multiphase mixture at lower calcination temperatures to a stable, single-phase rock-salt structure at 1000 °C. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) mapping show unique elemental domain segregation, with p-type (Cu, Ni, Co) and n-type (Zn, Mg) semiconductor domains forming multiple internal interfaces. These interfaces facilitate two key polarization mechanisms: (1) interfacial (Maxwell–Wagner–Sillars) polarization within grains, driven by charge accumulation at domain boundaries, and (2) space charge polarization across grain boundaries. Dielectric measurements reveal strong frequency dependence, with high dielectric properties at low frequencies suitable for charging applications and reduced dielectric values at high frequencies, beneficial for discharging processes such as regenerative braking in electric vehicles. This work demonstrates the potential of electronic structure design in HEOs to tailor dielectric properties for advanced applications, including tunable radio frequency (RF) devices, wireless communication, adaptive energy storage systems, and electric vehicle technologies.