Abstract: Sol precursors were prepared by the cosolubilized hydrousgel process using titanium butoxide and lanthanum
acetate as well as barium acetate. After condensation and drying, the wet gel and dry gel were obtained respectively. Dry gel ground and screened
was pressed into disc and sintered at different temperatures for holding different time to fabricate ceramic sensors. The measurement of humidity
sensitivity and gas/alcoholic sensitivity (seven kinds of gases H₂, CH₄, CH₂=CH₂, CH₃CH=CH₂, CO, C₆H₆ and gaseous CH₃CH₂OH) of these sensors were performed. The humidity sensor displays high sensitivity: S=5×10⁴kΩ/RH(%) (relative
humidity RH=32.8%～93.6%); good linearity: r=0.998; minimum humidity hysteresis: <4%; response time: τ=110s; and fine selectivity: sensitivity-less to above seven kinds of gases. The microstructure was characterized by SEM, AFM and XRF to confirm the
morphology, perovskite phase and surface roughness and whole element analysis. The mechanism of lanthanum modification was discussed that
titanium ion Ti⁴⁺ can capture a free electron. It is easy for this electron to jump into the conduct band due to non-equivalent substitution
of Ba²⁺ by rare earth ion La³⁺.

Key words: modification of La³⁺-doped barium titanate （La_xBa_1-x ceramic element, humidity sensitivity, microstructure characterization