| During past decades,pyroelectric materials have been widely used in pyroelectric detectors.The intrinsic pyroelectric materials mainly use the pyroelectric effect produced by the spontaneous polarization with the change of temperature.Since intrinsic pyroelectric materials do not need exterinal field,and they have excellent temperature stability near room temperature,low noise and reversible pyroelectric behavior,they have been regarded as the future direction of development.(Bi0.5Na0.5)TiO3 material has typical perovskite structure.It has rhombohedral phase at room temperature with good ferroelectric,piezoelectric and pyroelectric properties.Compared with other lead-free pyroelectric ceramics,BNT ceramics have been regarded as one of most promising alternative lead-free ceramics due to its high pyroelectric coefficient?p?,high remnant polarization Pr?around 38?C/cm2?,high Curie temperature Tc?around 320°C?,low-cost,and simple technology.Though,the pyroelectric properties including pyroelectric coefficient?p?and figures of merit?FOMs?of BNT-based materials have been enhanced greatly.Some BNT-based ceramics has higher p compared with PZT-based ceramics.However,the largest disadvantage of BNT-based ceramics is low depolarization temperature?Td?,which hinders their practical application.This is mainly because pyroelectric ceramics need to undergo a series of processing,such as wax-mounting of the ceramics wafers,and soldering process in surface mount technology?SMT?when they are being made for infrared detectors.The material should keep its pyroelectricity during all these processes that require high-temperature.In the case of BNT-based pyroelectric ceramics,partial or complete depolarization will happen during processes mentioned above,resulting in loss of pyroelectricity.Therefore,high Td,good thermal stability,and excellent pyroelectric properties are all essential factors for designing and fabricating pyroelectric ceramics for the sake of their wide practical usage.In this paper,BNT-based ceramics were synthesized by a conventional solid-state reaction method.Samples with high density and excellent properties were prepared by adjusting the composition,synthesis temperature and sintering temperature.The effect of BNN contents and sintering process on phase structure,microstructure,ferroelectric,dielectric,pyroelectric properties and thermal stability of BNT-based ceramics were systematically investigated.Meanwhile,we evaluate the materials potential in pyroelectric infrared detectors.The dielectric,ferroelectric and pyroelectric properties of BNT-based ceramics were optimized with the addition of BNN and BT.BNT-based ceramics with high depolarization temperature and good pyroelectric properties were obtained,which laid the foundation and provided important knowledge accumulation for the development of lead-free pyroelectric materials.?1??1-x?BNT-xBNN?x=0,0.02,0.03 and 0.04?lead-free ceramics were synthesized by a conventional solid-state reaction method.The effect of BNN contents on phase structure,microstructure,ferroelectric,dielectric,pyroelectric properties and thermal stability of?1-x?BNT-xBNN ceramics were systematically investigated.The pyroelectric coefficient?p?at room temperature increased gradually from 3.01×10-8C/cm2K at x=0 to 5.94×10-8C/cm2K at x=0.04.The dielectric loss?tan??and dielectric constant??r?decreased first with the small amount of BNN content,then increased slightly with further BNN addition,acquiring the minimum tan?and?r at x=0.02.When x=0.02,the optimal over-all properties were observed with p=4.13×10-8 C/cm2K,Fi=1.47×10-10m/V,Fv=3.57×10-2m2/C and Fd=2.56×10-5Pa-1/2.Meanwhile,the Td of 0.98BNT-0.02BNN ceramics is up to195°C.?2?We prepared 0.8BNT-0.2BT ceramics and studied its microstructure,dielectric properties,pyroelectric properties,and thermal stability.Its pyroelectric coefficient p,Fv,and Fd at room temperature are 2.66×10-8C/cm2K,2.95×10-2m2/C,and1.68×10-5Pa-1/2 respectively at 1 kHz.The p is higher than that of many other lead-free materials which also depolarize at high temperature such as SBN-based,KNN-based,and CaBi4Ti4O15-based bismuth layer-structured materials.It has the highest depolarization temperature?Td=209°C?compared with other BNT-based lead-free ceramics.It can endure high-temperature environment?180°C?for half hour with the value of p at room temprature remains90%of its initial value,demonstrating that the0.8BNT-0.2BT samples show excellent thermal stability.?3?We prepared 0.8BNT-0.2BT+0.1ZnO samples and found that:The depolarization temperature of 0.8BNT-0.2BT+0.1ZnO is high up to225?,which is about 20?higher than that of 0.8BNT-0.2BT ceramics.0.8BNT-0.2BT+0.1ZnO ceramics have good pyroelectric properties with p=2.20×10-8C/cm2.?4?After the measurement of ferroelectricity under hydrostatic pressure,we found that the ferroelectric properties of?1-x?BNT-xBNN?x=0.02,0.04?,0.8BNT-0.2BT and0.8BNT-0.2BT+0.1ZnO ceramics are stable.When the hydrostatic pressure is high up to 400 Mpa,all samples had relatively stable ferroelectric properties with negligible depolarization. |
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