Negative Capacitance Phenomenon and Origin in Alkali Niobate Film with Self-Assembled Lattice Faults

Abstract

Negative capacitance (NC) is an important phenomenon both in terms of the underlying fundamental science and its potential device application value. Achieving NC with adequate tunability in a scalable and reliable way is highly demanded for industrial applications. Herein, an electric-field-induced NC phenomenon and inductance-like behavior in alkali-deficient potassium sodium niobate thin film with self-assembled planar faults are demonstrated. Our in-depth investigation with the help of atomic-scale microscopy and high-temperature dielectric, conductivity, and X-ray studies revealed that the compensated electronic charge at the planar faults is localized as bound polarons which convert to free polarons at high temperature as well as by an increased electric field. The collective response of such polaronic charge along the planar faults under an oscillating electric field results in the observed NC phenomenon and inductance effect. Large NC values are obtained which can be tuned in terms of magnitude and operating frequency by controlling the concentration of the free polarons via external DC bias. This work underpins the unique feature of the defect architecture obtained in the alkali deficient KNN film and provides a novel material design strategy and fundamental framework to realize NC and related exotic phenomena in defect-engineered oxide materials.