Molten-salt synthesis of Ba_5−xSr_xNb₄O₁₅ solid solutions and their enhanced humidity sensing properties

Layered perovskite-type niobates A₅Nb₄O₁₅ (A = Ba, Sr) are thought to be good candidates for microwave dielectric and water-splitting applications, but traditional solid-state syntheses of these compounds usually require high temperatures and complicated procedures. In this work, Ba_5−xSr_xNb₄O₁₅ (x = 0 − 5) perovskite solid solutions were obtained using a facile molten salt synthetic method. The crystal structure of Ba_5−xSr_xNb₄O₁₅ solid solutions were characterized by X-ray diffraction (XRD). Crystal structure parameters with different Sr²⁺ concentrations show that the lattice parameters and unit cell volumes of Ba_5−xSr_xNb₄O₁₅ decrease with increasing [Sr²⁺]. The humidity sensing behavior of Ba_5−xSr_xNb₄O₁₅ solid solutions was investigated over a wide relative humidity (RH) range, from 11% to 95%. Ba₂Sr₃Nb₄O₁₅ shows the highest sensitivity among the obtained samples with a humidity hysteresis of ca. 4% RH. The response-recovery times of the Ba₂Sr₃Nb₄O₁₅ sensor are only 2 s and 17 s as the humidity alternates between 11% and 95% RH, respectively, showing excellent potential as a humidity sensing material for practical applications.