New frontiers in ceramic composites: tunable electromagnetic interference shielding by realizing negative permittivity in SnO2/LaNiO3 nanocomposites

Abstract

As electronic systems become progressively more compact and complex, the demand for lightweight, thermally stable, and metal-free electromagnetic interference (EMI) shielding materials continues to grow. Conventional metal-based composites are limited by environmental instability, high density, and narrow shielding bandwidth. In this study, we report nanostructured SnO₂–LaNiO₃ (SLN) composites as tunable conducting ceramic structures for metal-free EMI shielding. LaNiO₃, a conductive perovskite oxide, is incorporated into the SnO₂ matrix to mimic metallic properties, enabling precise control over charge carriers and tuning the electrical and dielectric responses. X-ray diffraction confirms the retention of individual phases in the composites, ensuring stability without chemical interactions. For devices capable of working at high temperatures and radiofrequencies, measurements were conducted as a function of temperature and frequency (100 Hz–2 MHz, RT–600 °C). Composites with ≥10 wt% LaNiO₃ display a transition from positive permittivity to strongly negative permittivity at and above room temperature, consistent with free-carrier plasma oscillations described by Drude theory. This transition is further verified by scanning electron microscopy, which shows the formation of percolative (conductive) networks with increasing LaNiO₃ content. As a result, conductivity increases due to a shift in the conduction mechanism from oxygen vacancy-driven ionic conduction to electron hopping between Ni²⁺ and Ni³⁺ sites. A significant drop in activation energy from 10 to 30 wt% LaNiO₃ further supports enhanced electronic conduction. Impedance (Z) and phase angle (φ) analyses indicate a shift from capacitive to inductive behavior, with the shielding mechanism changing from absorption-dominated (positive ε) to reflection-dominated (negative ε). In both regimes, the total shielding effectiveness exceeds 30 dB. The shielding effectiveness of SLN10 (25 dB) and SLN20 (37 dB) is achieved through absorption, while SLN30 (33 dB) achieves it through reflection. These results establish conductive perovskite-based composites as a promising, scalable, and metal-free solution for next-generation EMI shielding technologies.