Papers by Keyword: Pyroelectric Coefficient

Abstract: Infrared detection based on polymeric materials is continuously developed in order to be cheap and easy to processing and also having high pyroelectric coefficient to convert heat to electrical signal. PANI/DBSA was blended with polyvinylidene fluoride (PVDF) with different weight ratios to improve pyroelectric coefficient and electrical conductivity of PVDF. The temperature dependence of the electrical conductivity is measured in the range of 20-100 °C It was found that the pyroelectric coefficient increased from 1.5×10^-8 C/m² °C for pristine PVDF to 2.61×10^-5 C/m² °C at 25 wt.% PANI at 30 °C. The infrared detector circuit connected to the gate of a voltage follower JFET with high input impedance was designed to convert the high output impedance of the sensor into the output resistance. The output from the sensor and JFET is amplified in two stages of operational amplifier with high voltage gain with low noise.

Abstract: A dynamic current method used to measure pyroelectric coefficient (p) for pyroelectric material is described in detail in this paper. The hardware part of the system includes pre-converting circuit, post amplifier circuit, wave-filter circuit, analog-to-digital conversion circuit, temperature test circuit and LCD display panel circuit. The maximum magnification time of amplifier circuit of system is 11300 and the band-stop frequency center for wave-filter circuit is 50 Hz and it's second harmonics 100 Hz. Finally, the measurement system is used to test p parameter of LiTaO₃ crystal slice. The lowest p parameter of LiTaO₃ crystal with a value of 6.08×10^-9 C/cm^{2 o}C is achieved at 32.5°C.

Abstract: Lithium tantalate (LT) is a kind of excellent pyroelectric materials that can be made into high performance pyroelectric detector. As the detector voltage response and detection rate inversely proportional to the thickness of the infrared sensing element, So the thinning of lithium tantalate crystals becomes a key of success. This design uses CMP method to produce 50 μm thickness of LT wafer, and via charge integration method with computer automatic test system to test the pyroelectric coefficient of crystals with different thickness and surface roughness. The pyroelectric coefficient of crystal achieved 203 μC·m^-2k^-1 proves the favorable pyroelectric properties.

Abstract: 0.7BaO·0.3SrO·0.3Nb₂O₅·0.7TiO₂ (SBN/BST) composite ceramics werefabricated using a Powder-Sol (P-S) method with Nb₂O₅fine powder suspended in the barium strontium titanate (abbreviated as BST) solsolution. By X-ray diffraction (XRD) investigations, it is found that thetetragonal tungsten bronze (TTB) phase and perovskite phase were co-present incompositions. The average grain size of BST and SBN phase is 140 nm and 2.2 μm,respectively. The room temperature relative dielectric constant is 1445 forthis sample measured at 1 kHz and zero bias. In the room temperature, thepyroelectric coefficient of the 0.7BaO·0.3SrO·0.3Nb₂O₅·0.7TiO₂is 39 nc/cm²·°C. The maximum value of F_D is about 2.4×10^-5 Pa^-1/2at 45°C.

Abstract: In order to improve the properties of nano graded ferroelectric films (NGFF), the generalized Ginzburg-Landau-Denvonshire (GLD) theory is used to investigate the ferroelectric and pyroelectric properties of NGFF. A function is introduced to describe the local structure of this graded film. The numerical results show that parameter and film thickness are two very important factors that influence the ferroelectric and pyroelectric properties of films, larger values lead to smaller spontaneous polarization and lower pyroelectric peak Local structure in NGFF leads to flatten the polarization distribution, which raises the spontaneous polarization of components with lower transition temperature, but reduces spontaneous polarization of components with higher transition temperature.

Abstract: In order to improve the pyroelectric properties of nanograded ferroelectric films (NGFF), and provide a theoretical reference for practical applications, the generalized Ginzburg-Landau-Denvonshire (GLD) theory is adopted to investigate the pyroelectric properties of the NGFF. A function is introduced to characterize the local structure in nanograded films. Influence of the local structure, film thickness and external electric field on the polarization distribution and pyroelectric properties are mainly discussed. The numerical results show that parameterand film thickness are two very important factors that influence the film properties, larger values lead to smaller spontaneous polarization and lower pyroelectric peak. Different directions of the external electric field can lead to greatly different effects on pyroelectric behaviors, whose effects is to expand the working temperature region, or else, change the order of phase transition.

Abstract: The dielectric and pyroelectric properties of ferroelectric thin films coated with two semiconducting electrodes are studied in the frame work of Ginzburg-Landau-Devonshire theory. Due to the depolarization effect produced by the surface polar charges cannot be completely screened, the contribution of the semiconducting electrodes is included in the free-energy functional. The dielectric susceptibility and the pyroelectric coefficient are calculated respectively as functions of temperature and film thickness. A comparison with the results of investigations performed for perfectly conducting electrodes shows that the effects of semiconducting electrodes can induce a transition from the ferroelectric phase to paraelectric phase, changing the phase transition from the second order to first order, and greatly improving the dielectric susceptibility and pyroelectric coefficient.