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In the application of thin ferroelectric films to IR sensors, problems may arise to affect the sensitivities of the devices. The effects to influence the pyroelectric properties can be mainly categorized into two groups. One is the intrinsic effect due to the reduction in grain size. The other is the effect caused by residual stress. In this paper the stress effect on the pyroelectric properties of PbTiO 3 thin films will be studied by using the Landau-Ginsburg-Devonshire (LGD) phenomenological theory. It is found that a compressive stress increases the figure of merit while a tensile stress increases the pyroelectric coefficient for the films with the polarization vectors normal to the surface.

Effect of calcium substitution on the A-site of Zr-rich lead zirconate titanate Pb(Zr 0.94 Ti 0.06 )O 3 and Pb(Zr 0.92 Ti 0.08 )O 3 is studied. It is found that the rhombohedral structure of Zr-rich lead zirconate titanate changes to tetragonal and finally to cubic with increasing amount of calcium substitution. Both the dielectric constant and the Curie temperature decrease with the substitution of calcium on the A-site of the ABO 3 perovskite structure. A pyroelectric current peak is observed which is resulted from the phase transition from the low temperature rhombohedral ferroelectric phase F R ( LT ) to the high temperature F R ( HT ) one. Small amount of calcium substitution increases the peak value and also shifts the peak position to higher temperatures. However, further increase in the calcium content lowers the peak value and finally smears out the peak.

The effect of CdO doping on microstructure, conductance and gas-sensing properties of SnO 2 -based sensors has been presented in this study. Precursor powders with Cd/Sn molar ratios ranging from 0 to 0.5 were prepared by chemical coprecipitation. X-ray diffraction (XRD) analysis indicates that the solid-state reaction in the CdO–SnO 2 system occurs and α-CdSnO 3 with pervoskite structure is formed between 600 and 650°C. CdO doping suppresses SnO 2 crystallite growth effectively which has been confirmed by means of XRD, transmission electron microscopy (TEM) and BET method. The 10 mol% Cd-doped SnO 2 -based sensor shows an excellent ethanol-sensing performance, such as high sensitivity (275 for 100 ppm C 2 H 5 OH), rapid response rate (12 s for 90% response time) and high selectivity over CO, H 2 and i-C 4 H 10 . On the other hand, this sensor has good H 2 -sensing properties in the absence of ethanol vapor. The sensor operates at 300°C, the sensitivity to 1000 ppm H 2 is up to 98, but only 16 and 7 for 1000 ppm CO and i-C 4 H 10 , respectively.

FeSbO4-based semiconducting ceramics used as a promising candidate for sensing liquid-petroleum gas (LPG) are presented here for the first time. Precursor powders of FeSbO4 were prepared by two different methods (i.e., ball-milling and chemical coprecipitation). The solid-state reaction in the Fe2O3-Sb2O3 system was investigated by means of thermal gravimetric-differential thermal analysis (TG-DTA) and X-ray diffraction (XRD). Based on our experimental results and previous work, the diffusion of antimony oxide onto α-Fe2O3 is assumed to be a controlling step of the solid-state reaction. Scanning electron microscopy (SEM) and the BET method were used to characterize the samples calcined at 550 to 1000 °C. It was found that a sudden change in specific surface area, crystallite size and particle size takes place between 550 °C calcining and 600 °C calcining, which has an obvious influence on gas-sensing properties. FeSbO4-based sensors operating at 370 °C show a high sensitivity and selectivity to liquid-petroleum gas (LPG) over H2 CO or i-C4H10. Addition of Pd shows a fair increase in sensitivity to LPG, but a remarkable improvement in response and recovery times which is advantageous for its practical application.

γ-FeOOH particles have been prepared by oxidizing Fe(CO3)x(OH)2(1−x) suspension which contains a proper amount of Y3+. Y2O3-doped γ-Fe2O3 having tetragonal structure could be obtained by dehydrating the γ-FeOOH powder. Thermostability of the γ-Fe2O3 sample is studied by means of thermal gravimetric-differential thermal analysis and X-ray diffraction. It is found that the phase transition temperature of γ-Fe2O3 → α-Fe2O3 is up to 725°C, which has the advantage of improving the long-term stability of γ-Fe2O3-based sensors. The Y2O3-doped γ-Fe2O3 sample calcined at 600 °C has much higher sensitivity and selectivity to hydrocarbon gases. When the sensors based on this material operate at 380 °C, the sensitivities are equal to 34 for 1000 ppm liquid petroleum gas (LPG), but only 3 for 1000 ppm H2 or CO.

The preparation, characterization and gas-sensing properties of the Sb 2 O 3 Fe 2 O 3 complex oxide system have been investigated. Raw powders (with Sb/Fe = 0.2–1.0) of this system have been obtained by chemical coprecipitation. Effects of the Sb/Fe ratio and calcining temperature on the phase constituents and microstructure are characterized by thermal gravimetric-differential thermal analysis, X-ray diffraction and transmission electron microscopy. In the Sb 2 O 3 Fe 2 O 3 system, Fe 2 Sb 2 O 7 can be used as a new type of gas-sensing material, which has a fair sensitivity to reducing gases. However, of all the samples the powder with Sb/Fe = 0.5 calcined below 800°C, composed of 50% α-Fe 2 O 3 and 50% Fe 2 Sb 2 O 7 , exhibits the highest sensitivity to some hydrocarbon gases such as C 2 H 2 , petrol and liquid petroleum gas (LPG). This is attributed to both very fine crystallites and the amorphous phase of α-Fe 2 O 3 existing in the sample.

In this paper, the authors have developed a method of preparing coprecipitated powder precursors of ZnO-SnO 2 complex oxide by using oxalic acid and ammonia as precipitants. The phase constituents, structure and average grain sizes of powder precursors calcined at 500–1000 °C have been studied by means of XRD and TEM, which have an obvious influence on the conductance-temperature (ω- T ) characteristics and gas-sensing properties. It is advantageous for the powder calcined at lower temperatures (500, 600 and 700 °C) to detect combustible gases. The perovskite type of ZnSnO 3 is the dominant phase in the powder calcined at 600 °C; it has a much better sensitivity and selectivity to C 2 H 5 OH gas than anti-spinel type Zn 2 SnO 4 , ZnO and SnO 2 . Therefore, it is reasonable to expect the appearance of a good alcohol sensor by using a ZnSnO 3 -based material with suitable additives.