Planar sensor of SrTi(1-x)Fe(x)O3-delta, x = 0.4 and 0.6, with perovskite structure was fabricated on alumina substrate using thick film technology. Electrical resistance was measured as a function of thermal treatment conditions, atmosphere, time and temperature. Sensing property was also measured as a function of temperature and the gases of O2, CH4, CO, CO2, NO and NO2. The resistance of SrTi(1-x)Fe(x)O3-delta is lower than those of SrTiO3 or SrFeO3. TCR (temperature coefficient of resistance) of zero over 550 degrees C was measured for the composition of SrTi(1-x)Fe(x)O3-delta after thermal treatment at 1100 degrees C in air atmosphere only. The perovskite SrTi(1-x)Fe(x)O3-delta didn't show any response to CH4, CO, CO2, NO and NO2, but an excellent response and recovery characteristics with oxygen concentration.
The physicochemical and electrical properties of Pd-deposited WO3 thin films were investigated as a function of Pd thickness, annealing temperature, and operating temperature for application as a hydrogen gas sensor. WO3 thin films were deposited on an insulating material using a thermal evaporator. X-ray diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to evaluate the crystal structure, microstructure, surface roughness, and chemical property of the films, respectively. The deposited films grew into polycrystalline WO3 with a rhombohedral structure after annealing at 500 degrees C. Adding Pd had no effect on the crystallinity, but suppressed the growth of WO3 grains. The Pd was scattered as isolated small spherical particles of PdO2 on the WO3 thin film after annealing at 500 degrees C, while it agglomerated as irregular large particles or diffused into the WO3 after annealing at 600 degrees C. PdO2 reduction under H2 and reoxidation under air were dependent on both the Pd deposition thickness and annealing conditions. The WO3 thin film with a 2-nm-thick Pd deposit showed a good response and recovery to H2 gas at a 250 degrees C operating temperature.
NTC thermistors of Y-Al-Mn-Fe-Ni-Cr-O systems were fabricated by using normal ceramic processing for wide temperature range measurement. Pt-Rh alloy as electrodes was inserted into the body during the forming process to increase the reliability of high temperature and to decrease the contact resistance. The properties were analyzed by XRD, SEM and resistance measurement. There are no distinct XRD patterns between Y 0.2 Al 0.1 Mn 0.27 Fe 0.16 Ni 0.27 O x and Y 0.2 Al 0.1 Mn 0.264 Fe 0.16 Ni 0.264 Cr 0.012 O x because of too small content of Cr 2 O 3 , as a dopant, to make peak difference or new phases within the XRD resolution. SEM images and resistance behaviors show the different properties. With the addition of Cr 2 O 3 as a dopant, the crystallinity and the grain size were decreased and increased, respectively. The resistance behaviors were similar but the values are low with Cr 2 O 3. The specimens show the straight line relationship between the electrical resistivity and the temperature over a wide temperature range, indicating NTC thermistor characteristics.
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