http://hdl.handle.net/10397/2471 Search the Channel search http://repository.lib.polyu.edu.hk/jspui/simple-search http://hdl.handle.net/10397/600 Title: Piezoelectric properties of 1-3 composites of PZT in P(VDF-TrFE) copolymer<br/><br/>Authors: Kwok, Kin-wing; Chan, Helen L. W.; Choy, Chung-loong<br/><br/>Abstract: PZT/P(VDF-TrFE) 1-3 composites were fabricated by embedding pre-sintered PZT rods in a pre-poled copolymer matrix. The rods were then poled using an electric field much lower than the coercive field of the copolymer. The electromechanical coupling factor k[sub t], and the resonance characteristics of the composites were measured. The resonance characteristics of the composites were found to be dominated by the individual PZT rods. Poling of the copolymer matrix results in broadening of the main resonance peak. For transducer applications, it is advisable to pole the copolymer and the PZT rods in the same direction as this gives a higher k[sub t] value. http://hdl.handle.net/10397/599 Title: Study on PZT4/VF₂/VF₃ piezoelectric 0-3 composites<br/><br/>Authors: Chan, Helen L. W.; Chen, Yong; Choy, Chung-loong<br/><br/>Abstract: PZT4/VF₂/VF₃ 0-3 composites with different volume percent of ceramic have been fabricated. The dielectric constants and electrical resistivities of the composites were measured as functions of temperature in order to find the optimum poling conditions. The electromechanical properties of the piezoelectric composites were also measured and compared to model calculations. http://hdl.handle.net/10397/598 Title: Structure of nanocrystalline powder and thin films of lead lanthanum titanate prepared by the sol-gel process<br/><br/>Authors: Zhou, Qifa; Chan, Helen L. W.; Zhang, Qingqi; Choy, Chung-loong<br/><br/>Abstract: Ultrafine powder and thin films of lead lanthanum titanate (PLT) were prepared by the sol-gel process. The structural variation of the powder with increasing annealing temperature was monitored by differential thermal analysis, thermogravimetric analysis and x-ray diffraction. The lowest temperature for the formation of nanocrystals in the powder was found to be about 500°C. Crystallites of various sizes were obtained by controlling the annealing temperature and time. Thin films of PLT were fabricated by spin casting the sol-gel solution onto Si(111) substrates and the microstructure was analyzed using a scanning electron microscope. By controlling the concentration of the precursor and the processing temperature, PLT thin films with uniform crystallite size could be prepared. http://hdl.handle.net/10397/597 Title: Resonance characteristics and polarization profile of partially poled P(VDF-TrFE) copolymer<br/><br/>Authors: Ploss, Bernd; Chan, Helen L. W.; Kwok, Kin-wing; Choy, Chung-loong<br/><br/>Abstract: Thick films of polyvinylidene fluoride/trifluoroethylene (P(VDF-TrFE) copolymer with the composition 80/20 mol-% were poled at elevated temperature. The dielectric spectrum of this film shows two resonance peaks which correspond to the fundamental and second harmonic of the thickness vibration mode. Even harmonics of the thickness mode are usually not observed as they are not coupled to the electrical excitation. Piezoelectric and pyroelectric profiling experiments using both the pressure wave propagation (PWP) method and the laser intensity modulation method (LIMM) show that the copolymer has an inhomogeneous polarization profile which leads to the observed second order harmonic. In particular, these methods indicate that an unpoled region exists near the cathode side of the sample. By fitting the observed dielectric spectrum to a model of two Lorentz oscillators, the oscillation strengths have been estimated and found to be consistent with those obtained from the appropriate Fourier coefficients of the measured pyroelectric profile.