| Recently, ferroelectric materials have been attracted more and more interest inthe research for their many application of the dielectric tunability, ferroelectric,pyroelectric and optical properties, etc. As more and more micromation anddensification development of modern devices, the preparation conditions andproperties of ferroelectric material are getting higher and higher. In order to meet therequirements of practical application, low-preparation conditions andhigh-performance access for ferroelectric materials are desirable. Therefore, to enrichand develop preparation methods of low-dimensional ferroelectric materials and toexplore and study on their structure and properties is of great significance not only forbasic research but also for practical applications of low-dimensional ferroelectricmaterials.On the basis of a systemic summary and a comprehensive analysis of theresearch background for ferroelectric materials, we select lead strontium titanate (Pb,Sr) TiO3(PST) as research object due to its some advantages. The fabrication andelectrical, optical properties of (Pb, Sr)TiO3ceramic, thin films and nanostructures areinvestigated in the PhD dissertation. The main results are given as follows:1, PST ceramics samples with different Pb/Sr ratio were prepared byconventional mixed oxide method. Some results are obtained as follows:(1) PST ceramics have typical perovskite-type structure. With the increase of Pb content,there is a tendency from the cubic to tetragonal phase. The scanning electron microscopymicrographs reveal that the addition of Pb can affect microstructure.(2) The dielectric properties of the PST ceramic samples were investigated. Thedependent frequency dielectric permittivity and dielectric loss exhibit that the dielectricconstant have few change with frequency variation and reveal PST ceramics haverelatively stable frequency characteristic. The dependent frequency dielectric permittivityand dielectric loss are investigated in the frequency range from100Hz to1MHz. The maximumpeak of the dielectric permittivity versus temperature curve was broaden and a frequencydispersion of the dielectric permittivity was observed for the PST20/80ceramics. The resultsobtained at frequency of10kHz reveal the Curie temperature linear increased with the leadcontent. The fitted curves of temperature versus inverse dielectric permittivity at10kHz for(PbxSr1-x)TiO3ceramics are consistent with Curie-Weiss law. Polarization has little effect onthe dielectric properties of PST50/50ceramic.(3) Ferroelectric properties of the samples were also tested at room temperature.It is found as the lead increases, ferroelectric properties of samples are more enhanced.Ferroelectric properties of PST50/50sample at different temperatures show that as thetest temperature rise and ferroelectric properties of samples fade. by extrapolation,the temperature with zero remanent polarization (phase transition temperature) isabout162°C. When the measurement temperature is above the phase transitiontemperature, the remanent polarization is not zero, which maybe due to the existed polarization macro domainin the samples.(4) The temperature dependence of pyroelectric coefficient for PST ceramics was measuredby a dynamic technique. At room temperature (25C), the pyroelectric coefficients and the FDvalue are434C/m2K,222C/m2K,262C/m2K,294C/m2K and21.82×10-6,10.89×10-6,10.59×10-6and13.6×10-6Pa-0.5for PST35/65, PST40/60, PST45/55and PST50/50, respectively.The high pyroelectric coefficients and figure of merits indicate that the PST ceramicsare potential materials for pyroelectric sensors.(5) C-V curve are used to characterize tunability properties of PST ceramicssamples. It is found that with the Pb content increase, the C-V curves exhibit thebutterfly shape implying ferroelectric properties, which is consistent with the P-E loopresults. When the lead content is0.3and0.35, tunability value and FOM are higherthan51%,49%and356,342, respectively. The high dielectric constant, tenability andFOM make PST ceramics as potential materials for application of microwavedielectric tunable devices.2. PST50/50films were prepared on Pt/Ti/SiO2/Si substrate and single-crystalsubstrate using Sol-gel method:(1) The effect of annealing temperature on the microstructure and electricalproperties were investigated. The results showed that the higher annealingtemperature can enhance the electric properties of PST50/50thin films.(2) PST50/50films on Pt/Ti/SiO2/Si substrates with and without LNO bufferlayer are prepared by Sol-gel method. It is found that LNO buffer layer can effectivelyimprove the electrical properties of PST50/50thin films.(3) The microstructures of PST50/50thin films on different single crystalsubstrates by sol-gel method are characterized. The XRD results indicate highorientation films were successfully obtained by sol-gel process.3, PST nanostructures were obtained by AAO template combined with sol-gelmethod and electrospinning:(1) Hollow PST nanotube structures is obtained by using an AAO template.PST50/50and PST60/40nanotubes embedded in AAO templates exhibit ferroelectricproperties. PL spectra show that PST40/60nanotubes have two emission peakscentered at356and400nm while PST50/50and PST60/40nanotube have threeemission peaks located at412,432,449nm, and413,433,451nm with the300nmexcitation wavelength. It may be resulted from a lot of oxygen vacancies, defects andthe different crystal structure due to the different Pb/Sr ratio.(2) PST50nanofibers were successfully prepared by electrospinning. Themicrostructure is characterized by XRD, SEM, FTIR, Raman method. PFM resultsshowed that single PST50/50nanotube behavior ferroelectric properties. |
PDF Full Text Request