| High performance and inexpensive pyroelectric infrared sensors play an important role in the field of thermal detection and imaging of objects, because of the advantages of high sensitivity at long-wavelength and room-temperature operation without cooling system. The uncooled focal plane arrays (UFPA) using pyroelectric materials exhibit the excellent properties, which can compete with that of focal plane arrays (FPA) using semiconductors. In the dissertation, (Ba,Sr)TiO3 ceramics and BST/PVDF 0-3 composites were prepared, and grain size effect on dielectric and pyroelectric properties of which were studied. The main results are as follows:1. (Ba,8fr)TiO3 powders with particle size of about 50 nm were prepared by Sol-Gel process and microwave sintering. BST gel was crystallized by microwave processing for the first time, and the studies show that transition phase was produced during microwave processing, and the synthesize temperature of perovskite phase was reduced from 1100'C to 900 "C. The nano-powders have a uniform distribution, and particle size is about one tenth of conventional powders.2. Adopting the (Ba,Sr)TiO3 ceramic powder with lower curie temperature and the polymer PVDF, the 0-3 type BST/PVDF composites was fabricated for the first time, and their dielectric and pyroelectric properties were studied. The results show that figure-of-merit (FOM) FD of composite is about 30 percent larger than that of BST ceramic. The thickness of composite film and the particle size of the ceramic powder can influence the dielectric and pyroelectric properties of the composites.3. The grain growth can be restrained by microwave sintering significantly, the density (Ba,Sr)TiO3 ceramic with smaller grain (less than 1 urn) can be obtained. In this work, the ceramic microwave sintered at 1310 "C for 15 minutes displays the fine grain size (about 0.32 urn) and higher relativity density (about 95%). The tetragonlity ratio of samples displays a maximum value at grain size of about 0.8 um.4. Grain size dependence of dielectric properties of (Ba,Sr)TiO3 ceramic were studied. At about 0.8 um, the dielectric constant of Bao.esSro.ssTiO3 ceramic at ambient temperature displays a maximum value, and the diffuseness parameter displays aminimum value. The dielectric properties of fine-grained samples have higher stability response with frequency and bias-fields. It was discovered for the first time that the microwave sintering samples have lower dielectric loss comparing with conventional sintering samples, the result is significant for preparing the higher Signal-to-Noise pyroelectric sensor.5. Grain size effect on pyroelectric properties of (Ba,Sr)TiO3 ceramic were studied for the first time. The results show that the pyroelectric coefficient increases as grain size decreases, reached a maximum value at about 0.8 urn, then decreases greatly with further decrease in the grain size. Under DC-bias fields, the pyroelectric peak was suppressed and broadened, and moved to higher temperature slightly. The pyroelectric jpjoperties of the fine-grained sample displays higher stability under DC-bias field. The ceramic sample with grain size of about 0.8 urn displays the largest figure-of-merit (FOM), which is the ideal pyroelectric material for UFPA.
|
PDF Full Text Request