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

A series of (Sr 0.4 Ce 0.4 )TiO 3 + 4% (in mass) Sr 2 CeO 4 + x % B 2 O 3 (SCTO + 4% SCO + x % B 2 O 3 for 1≤ x ≤ 5) composites were synthesized via solid-state reaction to investigate the effects of Sr 2 CeO 4 and B 2 O 3 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 B 2 O 3 -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 B 2 O 3 incorporation modified the TiO 6 network via BO 3 /BO 4 interactions. The ε r decreased from 113 (SCTO) to 27 at x = 5%, while τ f improved from +213 to +12×10 –6 /°C. 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 Sr 2 CeO 4 and B 2 O 3 . Optimal microwave performance was achieved at x = 5%, with Q×f = 43,603 GHz, ε r =27, and τ f of +12×10 –6 /°C. The study demonstrates that SCO and B 2 O 3 act as effective modifiers, enhancing densification and dielectric properties in SCTO-based microwave ceramics.