Akash Roy

Ag Doped

This paper reports humidity sensing studies of pure WO₃ and Ag doped WO₃ prepared through soft chemical route. Prepared powders have been given pellet shape by applying pressure of 350 MPa. Pellets have been annealed at temperatures of 400°C-700°C. When exposed to humidity, resistance of the pellets is found to decrease with increase in relative humidity (RH). Sensing element of Ag doped WO₃ annealed at 700°C shows average sensitivity of 2.14 M Ω/%RH in the 20%-90% RH range. For this sensing element, the average hysteresis in the value of sensitivity is within 1.00%. For the sensing element of Ag doped WO₃, the repeatability over different cyclic operations is within ±3.00% and ±1.00% of the measured values of sensitivity after four and six months, respectively. X-ray diffraction (XRD) pattern of this sensing element shows formation of Ag:WO₃ bronze. As calculated from Scherers formula, crystallite size for the sensing elements of pure WO₃ and Ag doped WO₃ are in 12-72 nm and 19-73 nm range, respectively. The average grain size as measured from Scanning Electron Microscopy (SEM) micrograph for pure WO₃ is 125 nm, and 147 nm for Ag doped WO₃, suggesting agglomeration of the crystallites in the sensing element to form larger grains.

{\rm WO}_{3}

Pellet samples of 2, 5, 10, 15, and 20 weight % of Cu2Odoped ZnO nanocomposites have been prepared through solid-state reaction route. These samples have been annealed at temperatures 200°C-500°C and then exposed to humidity in a chamber. Resistance of the pellets continuously decreased when relative humidity in the chamber was increased from 10% to 90%. The sample with 20% of Cu2O doped in ZnO showed best results with sensitivity of 4.78 MΩ/%RH for annealing temperature of 400°C. This sample manifests high reproducibility, less effect of aging and lower hysteresis for annealing temperature 400°. The response and recovery time of this sample is found to be 76 and 296 s, respectively. XRD pattern shows peaks of hexagonal zincite and monoclinic tenorite.

Nanomaterials as Relative Humidity Sensor

This paper reports characterization and humidity sensing studies of pure zinc oxide (ZnO) andAl₂O₃-doped ZnO nanomaterials prepared by solid-state reaction route. Pellet samples of ZnO-Al₂O₃ nanocrystalline powders with 3, 5, 10, 15, and 20 wt% of Al₂O₃ in ZnO were prepared. Pellet samples of pure ZnO were also prepared. Pellets were annealed at temperatures of 400 °C to 700 °C. Prepared powders were given pellet shape by applying pressure of 260 MPa. When samples were exposed to humidity it was found that as relative humidity (RH) increased, resistance of pellets decreased for the range of humidity from 10% to 90% RH range. Sample with 15 wt% of Al₂O₃ in ZnO and annealed at 700 °C showed the best results with sensitivity of 14.98 MΩ/%RH. For this sensing element repeatability over different cyclic operations was within ±2% of the measured values of sensitivity after six months. Response and recovery time of sensing element of 15% Al₂O₃ in ZnO were found to be 85 and 286 s, respectively. This sensing element manifested lower hysteresis, less effect of ageing and high reproducibility for annealing temperature 700 °C. X-ray diffraction pattern of this sensing element showed peaks of cubic gahnite and hexagonal corundum. Scherrers formula gave crystallite size for the sensing elements of pure ZnO and Al₂O₃-doped ZnO in 18-96- and 23-98-nm range, respectively. Average grain size measured from scanning electron micrograph for pure ZnO was 107 nm and for Al₂O₃-doped ZnO (AZ-15) 114 nm suggesting agglomeration of the crystallites in the sensing element to form larger grains.

Moisture Sensing Application of

Paper reports morphological and relative humidity sensing studies of ZnO-TiO2 nanocomposite powder pellets obtained through solid-state reaction route. When exposed to humidity, resistance of pellets decreases with increase in relative humidity from 10-90%. Sensing element with 15 weight % of TiO2 in ZnO shows best results with maximum sensitivity of 9.08 MΩ/%RH in 10-90% relative humidity range. This sensing element manifests smallest crystallite size of 71 nm as measured from XRD and lowest grain size of 207 nm calculated from SEM micrograph. This sensing element has the lowest value of activation energy, and hence higher electronic conduction.

{\rm Cu}_{2}{\rm O}

Paper reports morphological and humidity sensing studies of WO3 and WO3-ZnO nanocomposite pellets prepared in the weight % ratio of 10:1, 4:1 and 2:1 by solid-state reaction route. The pellets have been annealed at temperatures of 300-500°C. XRD pattern shows peaks of ZnWO4 formed due to solid state reaction between WO3 and ZnO. SEM micrographs show that the sensing elements manifest porous structure. Granulation and tendency to agglomerate seen in the SEM micrograph are due to the presence of zinc ions in ZnWO4. Nanoparticles are having their sizes in the range 37-182 nm. The average Kelvin radius at 20°C room temperature is 27 Ả. Humidity sensing application of the pellets has been studied in a humidity control cabinet. It is observed that as relative humidity increases, there is decrease in the resistance of pellets in the range 10-85% RH. Sensing element of WO3-ZnO in 2:1 weight % ratio shows best results in 10-85 % relative humidity range. The average sensitivity of this sample is 1.20 MΩ/%RH. This sensing element shows good reproducibility, low hysteresis and less effect of aging.

Doped ZnO Nanocomposites

In this paper we report application of Cu2O doped ZnO composite prepared by solid state reaction route as humidity sensor. Pellet samples of ZnO‐Cu2O nanocrystalline powders with 2, 5 and 10 weight% of Cu2O in ZnO have been prepared. Pellets have been annealed at temperatures of 200–500° C and exposed to humidity. It is observed that as relative humidity increases, resistance of the pellet decreases for the humidity from 10% to 90%. Sample with 5% of Cu2O doped in ZnO and annealed at 500° C shows best results with sensitivity of 1.50 MΩ/%RH. In this case the hysteresis is low and the reproducibility high, making it the suitable candidate for humidity sensing.

Application of Undoped and Al 2 O 3 -Doped ZnO Nanomaterials as Solid-State Humidity Sensor and Its Characterization Studies

Paper reports morphological and humidity sensing application of Cu2O doped ZnO composite prepared by solid state reaction. Pellet samples of ZnO-Cu2O nanocrystalline powders with 5, 10, 15 and 20 weight % of Cu2O in ZnO have been prepared. These pellets have been annealed at temperatures 200–500°C. When samples have been exposed to humidity, it has been observed that as relative humidity increases, resistance of the pellet decreases for the entire range of humidity from 10 % to 90 %. The sample with 20 % of Cu2O doped in ZnO shows best results with sensitivity of 4.23 MΩ/%RH when annealed at 500°C. This sensing element manifests lower hysteresis, less effect of ageing and high reproducibility for annealing temperature 500°C. For this sensing element the two values of activation energy corresponding to two slopes in Arrhenius plot are 0.0274 eV for the temperature range 200–400°C and 0.0839 eV for the temperature range 400–500°C. XRD pattern shows peaks of hexagonal zincite and monoclinic tenorite. As calculated from Scherers formula the particle size for this sensing elements is 119 nm and according to SEM micrograph 104 nm.

Characterization and Humidity Sensing Application of ZnO-TiO2 Nanocomposite

This study reports the humidity sensing characteristics of ZnO–WO3 nanocomposite. Pellet samples of 0–5 weight% ZnO in WO3 were sintered from 300 to 600∘C. When exposed to humidity, the resistance of the sensing samples was found to decrease with increase in relative humidity (RH). Five percent ZnO-doped WO3 showed maximum sensitivity of 20.95 M Ω/%RH in 15–95% RH range. Sensor parameters like reproducibility, aging, hysteresis, response and recovery times were also studied. Sensing mechanism is discussed in terms of sintering temperature, composition and crystallite size of the sensing element. It was observed that sensing mechanism is strongly based on annealing temperature and percentage of doping. The sensing samples have also been investigated by X-ray diffraction, scanning electron microscope (SEM) and Raman spectroscopy. The crystalline size of the sample was identified by powder X-Ray Diffraction data. The SEM analysis was used to study the surface morphology. The structure, phase and the degree of crystallinity of the materials were examined by Raman spectroscopy.

Relative Humidity Sensing Studies of WO3-ZnO Nanocomposite

Paper reports sensing studies of NO<inf>2</inf> gas by WO<inf>3</inf> (prepared through sol-gel route) and Ag doped WO<inf>3</inf> for operating temperatures 200°C, 250°C and 300°C, for NO<inf>2</inf> gas concentration of 0 to 100 ppm. Both pure WO<inf>3</inf> and Ag doped WO<inf>3</inf> show better sensitivity for the operating temperature of 200°C. WO<inf>3</inf> and Ag doped WO<inf>3</inf> both show increase in value of sensitivity with increasing concentration (ppm) of NO<inf>2</inf>. For concentration of 100 ppm, sensitivity for sensing element of Ag doped WO<inf>3</inf> over WO<inf>3</inf> increased by 25% for operating temperature 200°C. Response time of sensors depend on operating temperatures both for pure WO<inf>3</inf> and Ag doped WO<inf>3</inf>. Least response time was obtained for operating temperature of 200°C.