Phase-Driven Property Modulation in BiVO₄ Ceramics via Multi-ion Substitution for Next-Generation Wireless...

The growing demand for faster and more reliable wireless communication has increased the need for microwave dielectric ceramics with high performance and thermal stability. In this paper, we synthesized Bi_1-4x(La_xNd_xSm_xEu_x)VO₄ ceramics (0.025 ≤ x ≤ 0.1) via a conventional solid-state method at a low firing temperature range of 740-860 °C. Structural analysis was conducted using X-ray diffraction, high-resolution transmission eleectron microscopy, and Raman spectroscopy and showed a composition-driven phase transition from monoclinic scheelite (space group: I2/a) to tetragonal zircon (space group: I41/amd) near x ≈ 0.075, with a mixed-phase region observed at relatively lower substitution levels. This structural change had a direct influence on the dielectric properties: the permittivity (ε_r) decreased from 66.98 at x = 0.025 to 19.85 at x = 0.1, while the quality factor (Qf) increased from 7904 to 16240 GHz. A nearly temperature-stable point was identified at x = 0.055, where τ_f reached +8.42 ppm/°C, which is attributed to a compensation effect arising from A-site cation rattling. Far-infrared analysis confirmed that phonon absorptions dominate the dielectric response in the microwave region. To validate practical applicability, a microstrip patch antenna fabricated from the x = 0.055 ceramic achieved a return loss of -22.5 dB at 2.46 GHz, along with 98.8% radiation efficiency and a peak gain of 5.22 dB. These results highlight that controlling the multi-ion substitution and their ratios provides an effective strategy for tuning the phase composition and dielectric performance in BiVO₄-based ceramics, which has a strong potential for ISM-band communication devices and emerging wireless technologies.