Structure–Property Map for Bi _{1– <i>x</i>} La _<i>x</i> VO ₄ Ceramics: Polymorphism, Mixed Conduction, and Dielectric Response

The structural flexibility of BiVO4-based ceramics enables diverse electrical functionalities, ranging from oxide ion conductivity to promising dielectric performance. This study investigated the structural evolution, electrical transport, and dielectric behavior of Bi1–xLaxVO4 (0 ≤ x ≤ 1) ceramics, in which Bi3+ is progressively substituted by La3+. Using variable-temperature X–ray diffraction (VT–XRD) and neutron powder diffraction (NPD), the phase transitions and crystallographic parameters were systematically analyzed. La3+ substitution induces a structural transformation from monoclinic fergusonite-type BiVO4 to tetragonal zircon-type BiVO4 and, ultimately, to a monoclinic monazite-type LaVO4 phase. Impedance spectroscopy and EMF measurements reveal that electronic conduction dominates across the series, with Bi0.8La0.2VO4 exhibiting the highest conductivity of 2 × 10–3 S cm–1 in air at 700 °C. Dielectric characterization shows that La3+ incorporation slightly improves thermal stability, with the temperature coefficient of resonant frequency (TCF) in Bi0.9La0.1VO4 improving from −280 to −156 ppm/°C. In addition, it features a dielectric constant of 52 and a quality factor of 4360 GHz. These findings provide comprehensive insight into the structure–property relationships in La-substituted BiVO4 ceramics and demonstrate their potential for applications in electronic and energy-related devices.