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An investigation of novel electroceramic structures for new sensor applications
Nan, Bo ; Liedermann, Karel (oponent) ; Milne, Steven (oponent) ; Button, Timothy William (vedoucí práce)
Piezoelectric ceramics are widely used in many applications and industries, but the traditional materials usually contain lead, which can undermine the environment and do harm to children. Most countries have therefore established laws or timetables to gradually minimize the consumption of lead, and research on lead-free compositions to substitute the lead-based counterparts has become a hot topic in recent years. However, investigations on transforming the innovative lead-free ceramics to their application are seldomly reported. In this thesis, one of the promising candidates in piezoelectric lead-free ceramics, (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, has been chosen to investigate methods for decreasing its high sintering temperature by doping with lithium carbonate and synthesizing the powder by a sol-gel technique, in comparison with conventional powder synthesised by solid-state routes. Samples fabricated from sol-gel powder doped with 0.5 wt.% lithium carbonate and sintered at 1300°C for 2 hours exhibited d33 = 447 ± 9 pC N–1, Curie temperature 98.7 °C and grain size 7.0 ± 0.3 µm. Another important issue for the application of lead-free piezoelectric ceramic is its fabrication in various connectivities. By utilizing tape-casting and additive manufacturing techniques, piezoelectric ceramic has been processed into three different connectivities, namely 2-2, 3-3 and 1-3, to bridge the gap between materials science and materials engineering. Oil-based and water-based suspensions have been utilized for tape-casting in two steps and in one step, respectively. For oil-based tape-casting, carbon suspensions with a solids loading of 25 wt.% and BCZT suspensions with a solids loading of 65 wt.% have been developed for preparing crack-free green films. The problem of powder hydrolysis in aqueous suspensions has been solved by surface treating the powder with Al(H2PO4)3 enabling crack-free films to be tape cast in one step. Films sintered at 1500 C exhibited relative dielectric constant of 1207, dielectric loss of 0.018 at 1 kHz, remanent polarization of 7.54 µC/cm2 and coercive field (Ec) of 0.23 kV/mm at 3 kV/mm. To achieve 3-3 and 1-3 connectivities, a free-forming direct ink writing method has been applied in shaping BCZT. An ink formulation containing a solids loading of 41.6 vol.% BCZT with the processing additives (HPMC ~ 2.4 % and PEI ~ 0.03 %) endowed the feedstock with a viscoelastic behaviour, which was suitable for the printing process. 3-3 samples sintered at 1500 C exhibited the highest dielectric and piezoelectric properties, with Curie point = 86 C, tan = 0.021, remanent polarization = 4.56 µC/cm2, and d33 = 100 ± 4 pC/N. 1-3 samples sintered at 1500 C and infiltrated by epoxy exhibited a dielectric constant of 144 and dielectric loss of 0.035 at 1 kHz. This work has demonstrated the shaping of lead-free piezoelectric ceramics with excellent properties into complex device structures in a step towards their use in applications.
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An investigation of novel electroceramic structures for new sensor applications
Nan, Bo ; Liedermann, Karel (oponent) ; Milne, Steven (oponent) ; Button, Timothy William (vedoucí práce)
Piezoelectric ceramics are widely used in many applications and industries, but the traditional materials usually contain lead, which can undermine the environment and do harm to children. Most countries have therefore established laws or timetables to gradually minimize the consumption of lead, and research on lead-free compositions to substitute the lead-based counterparts has become a hot topic in recent years. However, investigations on transforming the innovative lead-free ceramics to their application are seldomly reported. In this thesis, one of the promising candidates in piezoelectric lead-free ceramics, (Ba0.85Ca0.15)(Zr0.1Ti0.9)O3, has been chosen to investigate methods for decreasing its high sintering temperature by doping with lithium carbonate and synthesizing the powder by a sol-gel technique, in comparison with conventional powder synthesised by solid-state routes. Samples fabricated from sol-gel powder doped with 0.5 wt.% lithium carbonate and sintered at 1300°C for 2 hours exhibited d33 = 447 ± 9 pC N–1, Curie temperature 98.7 °C and grain size 7.0 ± 0.3 µm. Another important issue for the application of lead-free piezoelectric ceramic is its fabrication in various connectivities. By utilizing tape-casting and additive manufacturing techniques, piezoelectric ceramic has been processed into three different connectivities, namely 2-2, 3-3 and 1-3, to bridge the gap between materials science and materials engineering. Oil-based and water-based suspensions have been utilized for tape-casting in two steps and in one step, respectively. For oil-based tape-casting, carbon suspensions with a solids loading of 25 wt.% and BCZT suspensions with a solids loading of 65 wt.% have been developed for preparing crack-free green films. The problem of powder hydrolysis in aqueous suspensions has been solved by surface treating the powder with Al(H2PO4)3 enabling crack-free films to be tape cast in one step. Films sintered at 1500 C exhibited relative dielectric constant of 1207, dielectric loss of 0.018 at 1 kHz, remanent polarization of 7.54 µC/cm2 and coercive field (Ec) of 0.23 kV/mm at 3 kV/mm. To achieve 3-3 and 1-3 connectivities, a free-forming direct ink writing method has been applied in shaping BCZT. An ink formulation containing a solids loading of 41.6 vol.% BCZT with the processing additives (HPMC ~ 2.4 % and PEI ~ 0.03 %) endowed the feedstock with a viscoelastic behaviour, which was suitable for the printing process. 3-3 samples sintered at 1500 C exhibited the highest dielectric and piezoelectric properties, with Curie point = 86 C, tan = 0.021, remanent polarization = 4.56 µC/cm2, and d33 = 100 ± 4 pC/N. 1-3 samples sintered at 1500 C and infiltrated by epoxy exhibited a dielectric constant of 144 and dielectric loss of 0.035 at 1 kHz. This work has demonstrated the shaping of lead-free piezoelectric ceramics with excellent properties into complex device structures in a step towards their use in applications.
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