Geometry selective colossal negative dielectric permittivity in CaFe2O4 nanostructures

TL;DR

This paper reports a significant discovery of colossal negative permittivity in a single-phase calcium ferrite nanostructure, achieved solely through morphological restructuring without fillers, with potential applications in advanced materials.

Contribution

It demonstrates for the first time that nano hollow spherical morphology induces colossal negative permittivity in a single-phase material, unlike other morphologies.

Findings

Colossal negative permittivity observed in NHS morphology of CaFe2O4.

Different morphology (NSS) shows conventional dielectric behavior.

Phase inversion within the hollow cavity explains the negative permittivity.

Abstract

Negative permittivity metamaterial is a scientifically rich avenue due to its tremendous application in several arena of materials research including novel superlens, band-gap materials, invisibility cloaks, antenna and filter design. Traditionally, epsilon negative (ENG) behaviour is achieved in multi-phase composites with the addition of conducting metal fillers. However, this study reports colossal ENG feature in a single phase Calcium Ferrite for a particular nano hollow spherical (NHS) morphology, without the use of any filler. On the contrary, the same material synthesized in a different morphology, namely, nano solid sphere (NSS) shows conventional dielectric behaviour. Occurrence of ENG is successfully interpreted with the phase inversion of dominant polarization within the hollow cavity of NHS. This report marks a significant step in realizing colossal ENG in a single phase material just by restructuring the nanoscale morphology.