BaSc ₂ O ₄ : A Novel AB ₂ O ₄ ‐Type Low‐ k Microwave Dielectric Ceramic With Giant Positive τ _f for 5G/6G Frequency Compensation

ABSTRACT Developing low‐permittivity ( ε _r ), low‐loss microwave dielectric ceramics with near‐zero τ _f is critical for 5G/6G systems to solve signal delay and thermal stability issues. This study first reports BaSc ₂ O ₄ ceramics, which exhibit a rare combination: low ε _r (≈13), low loss (tanδ ≈ 1.46 × 10 ⁻³ ), and giant positive τ _f (+ 167 ppm/°C) for effective compensation in negative‐τ _f systems. Notably, it is the first discovery of BaSc ₂ O ₄ ’s low‐temperature phase transition (potential for cryogenic sensing) via dielectric temperature spectroscopy and in situ XRD; Rietveld refinement and Raman spectroscopy confirm a C 2/ c monoclinic structure (≈ 96.62% density). Far‐infrared spectroscopy reveals that the intrinsic Q × f value (∼ 39 000 GHz) significantly exceeds the experimental measurement, indicating potential for further improvement; P‐V‐L theory elucidates the relationship between microwave dielectric properties and crystal structure parameters; meanwhile, the designed device achieves a 2.4 GHz bandwidth S11 = −44.4 dB and S21 = 0 dB at 2.381 GHz (20°C), showing + 0.46 ppm/°C frequency temperature coefficient (from – 40°C to 120°C) via BaSc ₂ O ₄ ’s τ _f and metal electrodes’ thermal expansion, enabling unique potential applications like WiFi‐2.4G, IoT and RFID. A proof‐of‐concept 0.8Al ₂ O _{3 –} 0.2BaSc ₂ O ₄ composite achieves near‐zero τ _f with low ε _r (∼10) and loss (∼0.0016), and simulated 5.8 GHz antenna has 90.98% efficiency and 5.59 dBi gain, suitable for 5G/6G (C‐band) and ISM‐band.