The effect of oxygen stoichiometry on the humidity sensing characteristics of bismuth iron molybdate

Sears, W.M.

doi:10.1016/s0925-4005(00)00395-6

Cited by 70 publications

(35 citation statements)

References 34 publications

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“…At a low humidity, water vapour chemisorbs by a dissociation mechanism, forming hydroxyl ions at the surface [3]. Usually, an additional monolayer is added by 20% humidity with many more added at even higher humidity [18]. These physisorbed layers are easily removed by decreasing the humidity.…”

Section: Discussionmentioning

confidence: 99%

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

Faia

Furtado

Ferreira

2004

Sensors and Actuators B: Chemical

130

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A ceramic thick film humidity sensor was produced from an emulsion of titania powders by a spin coating technique using a low speed. Electrical measurements were taken between interdigital electrodes obtained by depositing silver paste on the oxide, then cured at 500 • C for 15 min. Different relative humidities of a dynamic atmosphere were obtained by mixing dry and 23 • C saturated synthetic air in convenient proportions. Complex impedance spectra of the titania sensor at various relative humidities (RH) and different temperatures were measured and compared. The humidity sensing behaviour is due to surface water molecules adsorption and capillary condensation. The proposed sensing mechanisms, explaining the registered impedance spectra, are a combination of proton hopping, hydronium electrical drift and diffusion, and electrolytic conduction. In the frequency range 1-400 Hz, resistance and capacitive reactance show variations of three to four-order magnitude over the RH range 10-100%. The curves representing the variations of resistance and capacitive reactance versus RH show clearly the existence of two dominant electrical charge transport mechanisms. A parameter called characteristic humidity is defined to represent the sensitive response of the sensor. It was found that the sensitivity was highly dependent on the frequency. This work also shows that, for the same RH, both resistance and capacitive reactance vary with the atmosphere temperature.

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Section: Discussionmentioning

confidence: 99%

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

Faia

Furtado

Ferreira

2004

Sensors and Actuators B: Chemical

130

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“…Many more physisorbed layers will be joined as humidity gets higher [20]. These physisorbed layers are easily and reversibly removed by decreasing the humidity.…”

Section: Basic Models Assumed For the Electrical Conduction And Polarmentioning

confidence: 99%

AC impedance spectroscopy: a new equivalent circuit for titania thick film humidity sensors

Faia

Furtado

Ferreira

2005

Sensors and Actuators B: Chemical

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The variation of the electrical signal with humidity in ceramic sensors is originated by the chemical and physical sorptions of water molecules existing in the atmosphere. The aim of the work described in the present paper is to establish an equivalent electrical circuit for the case of two titania thick-film samples. It is shown, at least for the temperature of 23• C, that the same type of circuit represents adequately these two samples for various relative humidities. Chemisorption and physisorption are responsible for the different charge transport mechanisms -ion hopping, ion diffusion and electrolytic conduction. Complex impedance data were obtained at the temperature of 23• C and various relative humidities, in the frequency range 0.1 Hz-40 MHz. The best and simpler circuit representation we found, which gives the best fitting for the Cole-Cole and Bode plots, consists of two RC parallel circuits in series with two constant-phase elements (CPEs). The values of the electrical components are tabled and, as an example, the Cole-Cole and Bode plots fitting obtained for one of our samples, the sample B, for 87.5% RH, in the frequency range 0.1 Hz-40 MHz is shown.

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“…With increasing humidity levels, water is physisorbed on top of the chemisorbed layer. Conduction probably occurs by the Grotthus transport mechanism [10]. At these high humidity levels the layers of physisorbed water molecules tend to condense in capillary pores, with a radius below r k , the Kelvin radius, given by,…”

Section: Humidity Sensitivitymentioning

confidence: 99%

“…The changes in the electronic conductance of the semiconductor in the presence of adsorbed water must also be considered. Water cannot directly inject a carrier into either the conduction or valence band of a metal oxide semiconductor [10]. A number of mechanisms have been suggested to account for the apparent electron donation from water molecules to oxides, including, non-dissociative adsorption with on electron donation, dissociative adsorption with one electron donation, and dissociative adsorption with two electron donation [12].…”

Section: Humidity Sensitivitymentioning

confidence: 99%

A Ceramic Thick Film Humidity Sensor Based on MnZn Ferrite

Arshaka

Twomey

Egan

2002

Sensors

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A ceramic thick film humidity sensor, produced from MnZn ferrite, is presented. The proposed sensing mechanism is a combination of proton hopping, hydronium diffusion, and vacancy donor traps releasing electrons into the conduction band. The sensor structure comprises a two-layer device; the first layer is an interdigitated conductor and the second layer is a 30µm thick sensing layer. The effects of sintering the sensing pastes in air and vacuum have been reported. The air-fired sample exhibits the highest humidity sensitivity (1.54%/RH%) and the lowest temperature sensitivity (0.37%/ o C). The vacuum-fired sample has the lowest humidity sensitivity (0.043%/RH) and the highest temperature sensitivity (0.77%/ o C). The sensitivity results indicate that the air-fired sample has the best potential for use in humidity sensing applications.

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The effect of oxygen stoichiometry on the humidity sensing characteristics of bismuth iron molybdate

Cited by 70 publications

References 34 publications

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

Humidity sensing properties of a thick-film titania prepared by a slow spinning process

AC impedance spectroscopy: a new equivalent circuit for titania thick film humidity sensors

A Ceramic Thick Film Humidity Sensor Based on MnZn Ferrite

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