The rapid advancement of electronic technologies leads to a widespread electromagnetic interference (EMI), which disrupts device performance and poses health risks, including neurological disorders, due to the prolonged exposure. Some emerging fields such as 5G communications, IoT, aerospace, and defense demand high-performance EMI shielding materials capable of operating under extreme conditions (e.g., high temperatures, radiation, and humidity) to ensure device reliability and data security. Conventional shielding materials (i.e., metals, carbon-based materials, and MXenes) have some limitations. Metals suffer from high density and corrosion, while carbon-based materials and MXenes degrade in high-temperature or oxidation environments. In contrast, ceramic materials, particularly perovskite oxides, offer superior thermal stability, corrosion resistance, and mechanical strength, making them promising candidates for next-generation EMI shielding. Among perovskite oxides, SrTiO₃ ceramics exhibit a high dielectric constant and superior insulating properties, but their intrinsically low conductivity limits their EMI shielding performance. The high-entropy design strategy, which incorporates multiple elements to enhance synergistic effects, provides a novel approach to improve electrical conductivity and thermal stability. Applying this high-entropy design to perovskite oxide ceramics can optimize their electromagnetic shielding performance under high-temperature environment, providing new research perspectives and technical pathways for developing novel high-temperature EMI shielding materials. In addition, the effect of high-temperature annealing on perovskite oxide performance remains unclear. Annealing in air leads to oxygen vacancy annihilation, causing structural and electronic changes that degrade both conductivity and EMI shielding efficiency. It is thus crucial to optimizing material design and ensuring stable performance under harsh environmental conditions. This study was to use a high-entropy design approach to develop perovskite oxide ceramics, and the EMI shielding properties in the X-band and their stability under high-temperature annealing were investigated. This work was to advance the development of robust, high-temperature EMI shielding materials via elucidating the annealing-induced structural and performance evolution, thus providing both theoretical insights and practical solutions for next-generation electronic and aerospace applications.

The perovskite oxide ceramics were synthesized via solid-state reaction with high-purity raw materials (i.e., SrCO₃, BaCO₃, CaCO₃, La₂O₃, Na₂CO₃, K₂CO₃, and TiO₂, all >99% purity from Aladdin Co., China). The powders were initially calcined at 400 ℃ for 3 h to remove moisture, and then ground by stoichiometric ball-milling in ethanol (150 r/min, 6 h). After rotary evaporation drying, the mixture was sintered in air at 1500 ℃ for 5 h to obtain pre-sintered powders, which were further ground into fine particles. The dense disk-shaped samples (φ26 mm) were prepared via vacuum hot-pressing (i.e., 10 Pa, 1400 ℃, and a heating rate of 10 ℃/min) at 70 MPa for 30 min, and subsequently annealed in air at 1000 ℃ for 1 h.

Two A-site high-entropy perovskite ceramics, i.e., (SrBaCaLaNa)_0.2TiO₃ and (SrBaCaLaK)_0.2TiO₃, are prepared through high-entropy design strategy. The XRD patterns indicate that the both ceramics maintain a single-phase cubic perovskite structure before and after 1000 ℃ annealing, and a peak shifts corresponding to average A-site ionic radii. The SEM images/EDS mapping and TEM images/EDS mapping demonstrate excellent elemental homogeneity without segregation, showing an effective solid solution formation. The Grain e analysis reveals a good structure stability after annealing due to the lower treatment temperature, compared to sintering temperature. The electron paramagnetic resonance (EPR) measurements show an enhanced oxygen vacancy concentration in high-entropy ceramics, compared to SrTiO₃. The electrical characterization indicates a room-temperature conductivity of 21 S/cm for (SrBaCaLaNa)_0.2TiO₃ and 16 S/cm for (SrBaCaLaK)_0.2TiO₃ due to La³⁺ aliovalent doping and oxygen vacancies. However, annealing causes 4-order conductivity reduction due to oxygen vacancy annihilation via oxygen re-filling. The dielectric analysis demonstrates superior properties in high-entropy ceramics (ε′=50-70, ε″=40-60), which are 20% higher than those of STO, where the conduction loss dominates the dielectric loss mechanism. The enhanced dielectric properties originated from increased dipole polarization and conduction loss associate with a higher oxygen vacancy concentration.

EMI shielding evaluation shows the superior performance with SE_Total >25 dB (99.6% efficiency) in X-band for both high-entropy ceramics, where reflection dominates the shielding mechanism (i.e., SE_R>10 dB, >90% reflectivity) due to large impedance mismatch. (SrBaCaLaNa)_0.2TiO₃ ceramic exhibits a slightly better shielding performance due to its higher oxygen vacancy concentration and conductivity. After annealing, high-entropy ceramics still outperform STO, while shielding performance degraded (i.e., SE_Total<20 dB), maintaining SE_R and SE_A at 10 dB. This result demonstrates that high-entropy design effectively enhances EMI shielding properties through lattice distortion effects, i.e., 1) modified local dipole moments from atomic displacement, and 2) enhanced dipole polarization through electron cloud redistribution. However, the performance degradation after annealing indicates that high-entropy design cannot completely prevent property deterioration in high-temperature oxidation environment, primarily due to oxygen vacancy and conductivity elimination.

A-site high-entropy perovskite ceramics, i.e., (SrBaCaLaNa)_0.2TiO₃ and (SrBaCaLaK)_0.2TiO₃, prepared via a high-entropy design, exhibited a single-phase cubic perovskite structure with a homogeneous elemental distribution. Compared to single-component STO ceramics, these high-entropy ceramics demonstrated higher oxygen vacancy concentration and electrical conductivity, leading to enhanced electromagnetic wave reflection and absorption. In the X-band, their total EMI shielding effectiveness exceeded 25 dB, with shielding efficiency surpassing of 99.6%. However, after annealing in air at 1000 ℃, the elimination of oxygen vacancies caused a notable decrease in conductivity, severely weakening polarization and loss capabilities. The reduction in complex permittivity diminished electromagnetic wave reflection and impaired dissipation ability, ultimately deteriorating EMI shielding performance. These results indicated that high-entropy design could improve the EMI shielding properties of perovskite ceramics, but it could not fully prevent performance degradation under high-temperature oxidative conditions.