Studies on calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0-3 nanocomposites

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Studies on calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0-3 nanocomposites


Author: Zhang, Qingqi
Title: Studies on calcium and lanthanum modified lead titanate/vinylidene fluoride-trifluoroethylene [PCLT/P(VDF-TrFE)] 0-3 nanocomposites
Degree: Ph.D.
Year: 1999
Subject: Composite materials
Fiber-reinforced ceramics
Polymeric composites
Nanostructured materials
Thin films
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Applied Physics
Pages: xvi, 217 leaves : ill. ; 30 cm
Language: English
Abstract: 0-3 calcium and lanthanum modified lead titanate (PCLT) / vinylidene fluoride-trifluoroethylene [(P(VDF-TrFE)] nanocomposites were fabricated. The physical structure and properties of the composites with both phases ferroelectric were studied. The investigation of the composite thin film for pyroelectric sensors application was performed. The PCLT [(Pb0.88Ca0.04La0.08)Ti0.98O3] ceramic powder that was used as ceramic phase of the composites was prepared using a sol-gel process. The structure and dispersing characteristics of the powder with crystallite size of 45 nm were investigated. An optimum solvent was found in order to prepare homogeneous PCLT/P(VDF-TrFE) composites. Ferroelectric PCLT bulk ceramics disks were prepared by sintering the PCLT powder derived from the sol-gel process and ferroelectric P(VDF-TrFE) copolymer thick films were prepared by a hot press process. The dielectric permittivities, piezoelectric and pyroelectric coefficients of these single-phase materials were measured and the data obtained were used as references in the composite modeling. The structure and phase transitions of the single-phase materials were also studied. 0-3 PCLT/P(VDF-TrFE) bulk composites with PCLT powder dispersed uniformly in a P(VDF-TrFE) matrix were fabricated using solvent-casting followed by hot-pressing. Structural analyses and electrical measurements were performed to investigate the effects and contributions of the individual phases to the composites. In the composites the XRD reflection peaks and IR vibration bands of both the ceramic and copolymer phases still appeared. The ferroelectric phase transitions of the copolymer still existed but the Curie temperature had a slight decrease. Compared to the copolymer, the 帣-relaxation peak of the composite slightly shifted to higher frequency and had broader distributions of relaxation time. Piezoelectric and pyroelectric activities of both the ceramic and copolymer phases were elicited by poling the composites at different temperatures. The piezoelectric and pyroelectric coefficients of the composites were measured and modeled. By poling the two phases in the same direction, the pyroelectric contributions from the two phases reinforced while piezoelectric contributions partially canceled, thereby minimizing the vibration induced noise. The results showed that the composites are good candidates for pyroelectric applications. To evaluate the composites for pyroelectric applications, composites in thin film form were first prepared on glass using the spin coating method and their electric properties were measured. Theoretical analyses on the performance of a multi-layered single pyroelectric detector were carried out based on the 1-D thermal diffusion equation. Silicon-based single-element and 1x8 integrated array pyroelectric sensors were fabricated with the composite as sensing materials. The current, voltage responsivites and specific detectivities of these sensors were measured and compared well with the theoretical calculations.

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