Browsing by Author "Reece, Michael J."
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Item Open Access Crystallization kinetics and enhanced dielectric properties of free standing lead-free PVDF based composite films(Elsevier, 2017-06-06) Meng, Nan; Mao, Rui; Tu, Wei; Odolczyk, Katarzyna; Zhang, Qi; Bilotti, Emiliano; Reece, Michael J.Ferroelectric composites, integrating dielectric ceramic fillers with mechanically flexible polymers, are promising materials for flexible electronic applications. Plenty of research has demonstrated the enhanced dielectric and ferroelectric properties of composite materials. However, the mechanisms responsible for these enhancements are not completely understood. Herein, we used typical dielectric materials, poly(vinylidene fluoride) (PVDF) and BaTiO3 (BTO), to study the effect of a dielectric filler on the crystallization, phase transformation and dielectric properties of PVDF. The crystallization of β-PVDF was not affected by the presence of BTO particles, but small amounts of BTO (<3 vol %) made PVDF crystallize into larger spherulites. This is linked to crystallization kinetic studies, which showed that BTO acted as a nucleation agent for large full ring banded spherulites when its content was less than 1 vol %. Furthermore, solid state drawing in the presence of BTO particles promoted the formation of β-PVDF with more pronounced preferred crystalline orientation at high drawing temperatures (120 °C). The dielectric and ferroelectric properties were enhanced with BTO filling. The 100 °C oriented drawn PVDF tape exhibited a dielectric permittivity of 14 (100 Hz) and remnant polarization of 0.080 C/m2 (10 Hz), which increased to 23 and 0.095 C/m2, respectively, after filling with 5 vol % BTO; neither resulting in high dielectric loss tangent (∼0.02) nor obvious current leakage. Moreover, the coercive field decreased from 80 to 50 kV/mm with increasing BTO content from 0 to 5 vol %.Item Open Access Enhanced thermoelectric performance of Cs doped BiCuSeO prepared through eco-friendly flux synthesis(Elsevier, 2017-11-10) Abdenour, Achour; Chen, Kan; Reece, Michael J.; Huang, ZhaorongThe synthesis of BiCuSeO oxyselenides by a flux method in air has been investigated. A maximum power factor of 230 μWm−1K−2 and a very low thermal conductivity of 0.42 Wm−1K−1 were obtained, leading to a high ZT value of 0.37 at 680 K for pristine BiCuSeO. With Cs doping, a large enhancement in electrical conductivity coupled with a moderate decrease in Seebeck coefficient lead to a power factor of 340 μWm−1K−2 at 680 K. In addition, Cs doping reduced the thermal conductivity further to 0.35 Wm−1K−1 at 680 K. The combination of higher power factor and reduced thermal conductivity results in a high ZT value of 0.66 at 680 K for Bi0.995Cs0.005CuSeO.Item Open Access Hybrid Flash-SPS of TiNiCu0.05Sn with reduced thermal conductivity(Elsevier, 2020-04-06) Gucci, Francesco; Saunders, Theo Graves; Srinivasan, Bhuvanesh; Cheviré, François; Ferluccio, Daniella A.; Bos, Jan-Willem G.; Reece, Michael J.TiNiCu0·05Sn was sintered using Spark Plasma Sintering (SPS) and a new derivative processing method, hybrid Flash-SPS (hFSPS). The high heating rate achieved (7700 °C/min) produced almost single-phase samples with high density. The sample sintered at 1040 °C showed a higher power factor and a lower thermal conductivity than the SPS sample, resulting in a higher ZT at 350 °C (0.44 vs 0.35).Item Open Access Oxidation protective hybrid coating for thermoelectric materials(MDPI, 2019-02-14) Gucci, Francesco; D’Isanto, Fabiana; Zhang, Ruizhi; Reece, Michael J.; Smeacetto, Federico; Salvo, MilenaTwo commercial hybrid coatings, cured at temperatures lower than 300 °C, were successfully used to protect magnesium silicide stannide and zinc-doped tetrahedrite thermoelectrics. The oxidation rate of magnesium silicide at 500 °C in air was substantially reduced after 120 h with the application of the solvent-based coating and a slight increase in power factor was observed. The water-based coating was effective in preventing an increase in electrical resistivity for a coated tethtraedrite, preserving its power factor after 48 h at 350 °C.Item Open Access Tuning of catalytic activity by thermoelectric materials for carbon dioxide hydrogenation(Wiley, 2017-10-06) Achour, Abdenour; Chen, Kan; Reece, Michael J.; Huang, ZhaorongAn innovative use of a thermoelectric material (BiCuSeO) as a support and promoter of catalysis for CO2 hydrogenation is reported here. It is proposed that the capability of thermoelectric materials to shift the Fermi level and work function of a catalyst lead to an exponential increase of catalytic activity for catalyst particles deposited on its surface. Experimental results show that the CO2 conversion and CO selectivity are increased significantly by a thermoelectric Seebeck voltage. This suggests that the thermoelectric effect can not only increase the reaction rate but also change chemical equilibrium, which leads to the change of thermodynamic equilibrium for the conversion of CO2 in its hydrogenation reactions. It is also shown that this thermoelectric promotion of catalysis enables BiCuSeO oxide itself to have a high catalytic activity for CO2 hydrogenation. The generic nature of the mechanism suggests the possibility that many catalytic chemical reactions can be tuned in situ to achieve much higher reaction rates, or at lower temperatures, or have better desired selectivity through changing the backside temperature of the thermoelectric support.