Engineering A-Site Multi-Doping in Perovskite Oxide LaCoO3 for Tailored Radio-Frequency Dielectric Response and Electromagnetic Shielding Applications

The growing demand for high-performance electromagnetic interference (EMI) shielding materials in modern communication and integrated electronics has stimulated interest in materials with tunable dielectric responses. In this study, a series of A-site-doped perovskite oxides—LaCoO3, (La0.5Sr0.5)CoO3, and (La1/3Sr1/3Ba1/3)CoO3—were synthesized via a sol–gel method to investigate their dielectric behavior in the radio-frequency (RF) range. Dielectric spectroscopy reveals that LaCoO3 exhibits a positive permittivity characteristic of semiconductors, whereas Sr substitution induces a metallic state in (La0.5Sr0.5)CoO3, whose dielectric response exhibits a Drude-like dispersion behavior within the measured RF frequency range. Further incorporation of Ba into the A-site results in ternary co-doping, suggesting a reduction in effective carrier transport and a shift in the characteristic dispersion frequency toward the low-frequency region. Consequently, (La1/3Sr1/3Ba1/3)CoO3 displays a near-zero permittivity at approximately 2.5 kHz, indicating a transition in the dominant reactive response from inductive-like to capacitive-like behavior, which is consistent with the impedance spectroscopy results. This work demonstrates that cation engineering at the A-site enables precise control over the RF dielectric response in perovskite oxides, offering a potential pathway for the design of tunable electromagnetic functional materials relevant to EMI shielding applications with tailored permittivity characteristics.