Improved humidity sensing through Mg substitution in LaFeO₃ perovskite

Perovskite-based LaFe_1-x Mg _x O₃ (x = 0.0, 0.1, and 0.3) humidity sensors are fabricated on alumina substrates with gold interdigitated electrodes via drop-casting method. All sensors exhibit distinct humidity responses over a relative humidity (RH) range of 11-96%, with capacitance increasing monotonically as RH increased. The calculated sensitivities are 6.79, 8.97, and 6.55 pF/% RH for x = 0.0, 0.1, and 0.3, respectively, indicating that Mg substitution at x = 0.1 significantly enhances sensitivity, likely due to the increased density of hydrophilic adsorption sites. All sensors exhibit very low hysteresis (0.04-0.15%), demonstrating highly reversible adsorption-desorption behavior. The response/recovery times are 9.9 s/1.9 s, 11.6 s/4.5 s, and 20.7 s/3.8 s for x = 0.0, 0.1, and 0.3, respectively, a trade-off between sensitivity and response dynamics at higher Mg content. Stability tests over 32 days at laboratory scale reveals performance degradations of 2.8%, 0.11%, and 0.78% for x = 0.0, 0.1, and 0.3, respectively, confirming that Mg substitution improves the long-term stability. Overall, the composition x = 0.1 provides the optimal balance between sensitivity and stability, highlighting Mg substitution as an effective strategy for improving perovskite-based humidity sensors.