BaSc ₂ O ₄ : A Novel AB ₂ O ₄ ‐Type Low‐ <i>k</i> Microwave Dielectric Ceramic With Giant Positive <i> τ _f </i> 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.