Stydy on Pyroelectric Effect and Properties of PZT-based Ceramics
|School||Huazhong University of Science and Technology|
|Course||Microelectronics and Solid State Electronics|
|Keywords||pyroelectric infrared detector PZT doping modification FRL-FRHphase transition composite-sintering|
Lead zirconate titanate （PZT） series of ceramics which abound with phase transitionin Zr-rich region have became the main material in preparation of uncooled infrared focalplane arrays due to their excellent pyroelectric properties. Pyroelectric infrared detectorsdeveloping to high sensitivity and wide work temperature range have proposed newacquirements that in a wide temperature range near room temperature PZT series ofceramics must have properties of high and stable pyroelectric coefficient, low dielectricconstant and loss, high figure of merit.Zr-rich PZT series of ceramics have drawn wide attention due to the FRL-FRHphasetransition which gives high pyroelectric coefficient. In this thesis, the FRL-FRHphasetransition properties were observed by changing the ratio of Zr/Ti firstly. When theZr/Ti=95/5and93.5/6.5, there was a very sharp peak of pyroelectric coefficient at26℃or40℃respectively (up to9.7×10-8C/cm2℃and7.8×10-8C/cm2℃). When theZr/Ti=90/10and87.5/12.5, the curve of pyroelectric coefficient depend on temperaturewas much flat (between3.5×10-8C/cm2℃and4.5×10-8C/cm2℃) while the dielectricconstant and loss were much low. For above all and to meet the acquirements of highsensitivity and wide work temperature range, further research was done in two aspectsbelow.On the one hand, PZT-based ceramics with Zr/Ti=90/10were doped to increase thepyroelectric coefficient overall. It was found that, by K doping the pyroelectric coefficientand figures of merit were increased while the dielectric constant and loss were reduced.The pyroelectric coefficient and figures of merit reached the maximum whenK2CO3doping quantity was1At%and0.5At%respectively. In the meanwhile, by properMn-Sb doping the ferroelectric rhombohedral phase was enhanced resulting in the greatimprovement of ferroelectric properties and increase of pyroelectric coefficient. Butunreasonable ratio of Mn/Sb or overdose of doping could lead to deterioration of dielectricproperties which effected figures of merit. The pyroelectric coefficient (about6×10-8C/cm2℃) and the figure of merit (about6.5×10-5Pa-1/2) reached the maximum whenMnO2doping quantity was1.5At%and Sb2O3doping quantity was0.5At%. On the other hand, PZT-based ceramics with Zr/Ti=95/5and93.5/6.5were chosen instudy on composite FRL-FRHphase transition, trying to broaden the phase transitiontemperature range and keep the high pyroelectric coefficient in a wider temperature range.It was found that, proper composite-sintering created an coexistence of multi-componentwhich would give an composite effect of FRL-FRHphase transition. The temperature rangewas successfully extended when the two starting materials were pre-treated at1100℃before mixed by the mass ratio of1:1. The pyroelectric coefficient was higher than6.3×10-8C/cm2℃and the figure of merit was higher than7.7×10-5Pa-1/2in the temperaturerange19℃to43℃. In the meanwhile, the dielectric and ferroelectric properties were alsoimproved.