Abstract
Despite the many attractive potential uses of ceramic materials as humidity sensors, some unavoidable drawbacks, including toxicity, poor biocompatibility, long response and recovery times, low sensitivity and high hysteresis have stymied the use of these materials in advanced applications. Therefore, in present investigation, we developed a capacitive humidity sensor using lead-free Ca,Mg,Fe,Ti-Oxide (CMFTO)-based electro-ceramics with perovskite structures synthesized by solid-state step-sintering. This technique helps maintain the submicron size porous morphology of the developed lead-free CMFTO electro-ceramics while providing enhanced water physisorption behaviour. In comparison with conventional capacitive humidity sensors, the presented CMFTO-based humidity sensor shows a high sensitivity of up to 3000% compared to other materials, even at lower signal frequency. The best also shows a rapid response (14.5 s) and recovery (34.27 s), and very low hysteresis (3.2%) in a 33%–95% relative humidity range which are much lower values than those of existing conventional sensors. Therefore, CMFTO nano-electro-ceramics appear to be very promising materials for fabricating high-performance capacitive humidity sensors.
Highlights
Humidity is a physical parameter which describes the degree of dryness of the atmosphere
In these equivalent circuits of such complex impedance plots, Rf stands for the resistance of the CMFTO electro-ceramic, which decreases as relative humidity (RH) increases, Cf is the capacitance of the CMFTO electro-ceramic and Zi is the interfacial impedance at the electrodes/CMFTO electro-ceramic [54,74]
The capacitance of the sensor of the CMFTO electro-ceramic increased from 3.2183 × 10−11 F to 9.9741 × 10−10 F as the RH changed from
Summary
Humidity is a physical parameter which describes the degree of dryness of the atmosphere. The mixed ionic and electronic conducting properties of perovskite-structured oxides provide advantages of higher selectivity, activity and stability than seen with simple transition metal oxides Their potential applications as cathode materials in oxygen permeation membranes (OPMs) for air separation [24], catalysts for hydrocarbon oxidation reactions [25,26], solid oxide fuel cells (SOFCs) [27] and catalytic membrane reactors (CMRs) for syngas production [28] have popularized their use among researchers. The CMFTO electro-ceramics were prepared by an innovative solid-state step-sintering process to get the desired morphology with lower density and high porosity This facile synthesis process is convenient, eco-friendly and controlled, compared to other synthesis techniques [29,30,31,32,33].
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