热释电材料性能及应用研究进展

Research Progress on Performance and Application of Pyroelectric Materials

热释电材料(pyroelectric material)是利用温度随时间的波动将热能转换为电能的一种材料,主要可用于能量转换器件及探测装置,其响应范围宽、灵敏度高、性能易于善调节,因此得到了广泛的应用。从热释电性能优值(figures of merit,FOM)的计算表达式出发,介绍了几种提高FOM,使热释电材料充分发挥性能的方式。总结了单晶材料、高分子有机聚合物及复合材料、金属氧化物陶瓷及薄膜材料各自的优势,以及热释电材料几项具体应用。并且对热释电材料在提高能量收集效率、向着集成化发展、开发新的器件以更好地应用到新兴领域等方面提出了展望。

Pyroelectric material was a type of material that converts thermal energy into electrical energy by using temperature fluctuations with time(i.e.d T/dt,where T was temperature and t was time).Pyroelectricity was the ability of some polar dielectric to generate a temporary current or voltage when they were heated or cooled.Pyroelectric materials had no symmetry center in the crystal internal structure and therefore possess spontaneous polarization.The change of temperature would cause internal strain,and the internal strain would cause relative displacement of the positive and negative charge centers,so the polarization of the pyroelectric material would be changed,and pyroelectric charges could be generated on the surface perpendicular to the direction of polarization.In order for material selection and performance evaluation,various figures of merit(FOM)had been derived,including current FOM(F_(i)),voltage FOM(F_(v)),detection FOM(F_(D)),energy harvesting FOM(F_(E)),etc.It had been found that ideal pyroelectric materials should have low volume specific heat capacity(C_(v)),dielectric constant(ε_(p))and dielectric loss(tanδ),while high pyroelectric coefficient(p).Pyroelec-tric performance could be improved by optimizing parameters in the preparation process,post-processing the material,heat treatment,element doping(e.g.,doping Mn in lead zirconium titanate(PZT)ceramics),and adjusting the structure(such as fabricating functionally graded tri-layered structure).Pyroelectric materials could be roughly divided into three categories:single crystal materials(such as triglycine sulfate(TGS)crystal and Pb_(5)Ge_(3)O_(11)(PGO)),organic polymers(such as polyvinyl fluoride(PVF)and polyvinyli-dene fluoride(PVDF))and composite materials(such as PVDF and PZT composite(PVDF-PZT)),metal oxide ceramics and thin films(such as Ba_(x)Sr_(1-x)TiO_(3)and Pb_(x)Zr_(1-x)TiO_(3)).The performance of pyroelectric single crystal was generally better than that of ceramic counterparts with same composition,but the preparation of single crystal pyroelectrics was costly.Pyroelectric organic polymers were suitable for the production of large-area flexible pyroelectric films,but the disadvantage was that their pyroelectric coefficients are rela-tively low.The properties of pyroelectric ceramic materials were easy to be optimized by changing the composition.Composites made from organic polymers and ceramics could combine the advantages of both materials,but how to improve the bonding between the two phases of composite materials to reduce the dielectric loss needed to be further investigated.Making pyroelectric materials in the form of metal oxide films could effectively reduce the volume specific heat capacity,which helped to improve detection sensitivity and integration.This kind of pyroelectric material could better adapt to the development direction of miniaturization and integration of function-al devices.The use of pyroelectric materials to make thermo-electric energy conversion devices(such as pyroelectric energy harvesters)held great promise.Electricity,refrigeration and heat pump cycles released large amounts of waste heat.Converting waste thermal energy into valuable electricity could contribute to the realization of sustainable resource development.Another important application of pyroelectric materials was pyroelectric detectors which could be used for fire detection,gas analysis detection,military detection,etc.This kind of detectors could effectively distinguish active biological heat sources from environmental heat sources,so they could be used in human intrusion detection,infrared imaging,and so on.They had outstanding versatility because the pyroelectric materials used could respond to various wavelengths in full wave band.A safety distance reminder device dedicated to measure the distance be-tween people and their body temperature was proposed in the year of 2020.When the distance detected by pyroelectric infrared sensors was too close,the sound alarm and light-emitting diode(LED)lights connected to the signal output end would issue a warning.This device contained components of pyroelectric materials could helpfully prevent people from gathering and reduce potential exposure to people.Pyroelectric materials had broad application prospects.It was of great significance to make full use of their advantages and con-tinue to explore new pyroelectric materials,devices and mechanisms in the future.