Researches On PLCT Pyroelectric Materials Used For Infrared Detectors

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 infrared focal plane arrays(UFPA)using pyroelectric materials exhibit the excellent properties, which can compete with that of infrared focal plane arrays(FPA)using semiconductors. It is mainly studied the PLCT pyroelectric ceramics. The pure perovskite phase has been obtained by solid-state method. The dielectric and pyroelectric properties of PLCT ceramics are systematically studied.TG-DTA analysis indicated that the perovskite PLCT could be formed at 700℃and began to melt at 1300℃. So the sintering temperature of PLCT ceramics should be limited below 1300℃. The XRD analysis indicated that the level of (110) crystallization had been improved with increased annealing temperature. It showed the grains began to grow up and increased at 1200℃, so the best sintering temperature was 1200℃.The pyroelectric PLCT ceramics had been fabricated from pre-synthesized PLCT powders by ball milling, moulding, removing binder and sintering. The results of study revealed that it could increased the pyroelectric coefficient by La-doping, but it also increased the dielectric coefficient. It could hardly affect on pyroelectric and dielectric characteristics by Ca-doping. By comparison we can conclude PLCT ceramics with x=0.1, y=0.1 exhibite good dielectric and pyroelectric characteristics.The dielectric and pyroelectric characteristics of Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ ceramics with different Mn contents and La contents were investigated. The results showed that the dielectric loss decreased with addition of Mn to the ceramics, and the pyroelectric coefficient increased with addition of Cr to the ceramics. Pb_0.8La_0.1Ca_0.1Ti_0.975O₃ ceramics by 1.0%mod Mn-doping exhibite the best properties: the dielectric constant is 369, the dielectric loss is 0.003, the pyroelectric coefficient is 6.0×10^-8C/(cm²K) and the figure of merits(FD) is 7.5×10^-5Pa^-0.5.The cure temperature of PbTiO3 ceramics which is not easy to obtain is very high. A tetragonal (ferroelectric)-cubic(paraelectric) phase transition is easy to occur by La-doping and Ca-doping. The cure temperature also decreases and the pyroelectric coefficient increases.