BaSc2O4: a novel AB2O4-type low-k microwave dielectric ceramic with giant positive τf for 5G/6G frequency compensation

Developing low-permittivity (εr), low-loss microwave dielectric ceramics with near-zero τf is critical for 5G/6G systems to solve signal delay and thermal stability issues. This study first reports BaSc2O4 ceramics, which exhibit a rare combination: low εr (≈13), low loss (tanδ ≈ 1.46 × 10−3), and giant positive τf (+ 167 ppm/°C) for effective compensation in negative-τf systems. Notably, it is the first discovery of BaSc2O4’s low-temperature phase transition (potential for cryogenic sensing) via dielectric temperature spectroscopy and in situ XRD; Rietveld refinement and Raman spectroscopy confirm a C2/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 BaSc2O4’s τf and metal electrodes’ thermal expansion, enabling unique potential applications like WiFi-2.4G, IoT and RFID. A proof-of-concept 0.8Al2O3 – 0.2BaSc2O4 composite achieves near-zero τf with low εr (∼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.

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