Low-loss (Sr,Ce)TiO₃—Sr₂CeO₄—B₂O₃ ceramics composite featuring balanced microwave dielectric properties for miniaturized wireless communication applications

A series of (Sr_0.4Ce_0.4)TiO₃ + 4% (in mass) Sr₂CeO₄ + x% B₂O₃ (SCTO + 4% SCO + x% B₂O₃ for 1≤ x ≤ 5) composites were synthesized via solid-state reaction to investigate the effects of Sr₂CeO₄ and B₂O₃ additives on their structural evolution and microwave dielectric properties. X-ray diffraction (XRD) and Rietveld refinement confirmed the dominant orthorhombic phase (O-phase), with SCO as a secondary phase, indicating a chemically stable composite system. HRTEM and SAED analyses further confirmed the formation of the O-phase through direct observation of the superlattice reflections. Microstructural evolution demonstrated B₂O₃-assisted liquid-phase sintering, reducing porosity (0.017 → 0.006) and increasing grain size (3.34 → 6.01 μm) with increasing x% (in mass). Raman spectroscopy verified octahedral tilting and Ce—O stretching, while B₂O₃ incorporation modified the TiO₆ network via BO₃/BO₄ interactions. The ε_r decreased from 113 (SCTO) to 27 at x = 5%, while τ_f improved from +213 to +12 × 10⁻⁶/℃. The reduction in ε_r arises from a complex interplay of internal factors (ionic polarizability) and external factors (porosity, and density), whereas the variation in τ_f is governed by compensating effects from Sr₂CeO₄ and B₂O₃. Optimal microwave performance was achieved at x = 5%, with Q×f = 43,603 GHz, ε_r = 27, and τ_f of +12 × 10⁻⁶/℃. The study demonstrates that SCO and B₂O₃ act as effective modifiers, enhancing densification and dielectric properties in SCTO-based microwave ceramics.