Jie Wu,Gaochao Zhao,Chengbing Pan,Peng Tong,Jie Yang,Xuebin Zhu,Lihua Yin,Wenhai Song,Yuping Sun
We report the structure, dielectric, ferroelectric and piezoelectric properties of Cr-Mn co-doped (1- y )BiFe 1- x Cr x O 3 - y BaTi 1- x Mn x O 3 (0≤ x ≤0.04, 0.2≤ y ≤0.27) ceramics. By varying both x and y , a series of samples near morphotropic phase boundaries exhibiting both high ferroelectric Curie temperature T C (∼580−643 °C) and relatively large piezoelectric constant d 33 are constructed. Especially, the sample with y = 0.24 and x = 0.02 is found to show coexistence of high depolarization temperature T d (∼551 °C) and relatively large d 33 ∼116 pC/N, superior to most of those of BiFeO 3 based high-temperature piezoceramics reported previously. The enhanced ferroelectric T C in the Cr-Mn modified samples can be ascribed to the combined effects of large lattice distortion and high tetragonal phase content. These results demonstrate that constructing morphotropic phase boundaries via considering simultaneously the role of lattice distortion might be effective route to realize high-temperature and high piezoelectricity in BiFeO 3 -based systems.
The optical absorptance of calcium-based composites used in direct solar-driven calcium-looping thermochemical energy storage systems should be improved. Experimental data obtained by thermogravimetric analyzer (TGA) cannot adequately describe the realistic performance of such calcium-based composites. In this work, calcium-based composites filled in a fixed bed reactor were directly irradiated by concentrated sunlight to examine the performance of thermochemical energy storage under different light illumination conditions. The effects of doping content and concentration ratio of sunlight on the cycling performance of the modified calcium-based composites were investigated under direct solar-driven conditions. The Cr/Mn co-doped CaCO 3 -based materials with a molar ratio of Ca: Cr: Mn = 100:4:8 could be efficiently operated under direct sunlight irradiation conditions because of a high optical absorption of 73.22 %, achieving gravimetric energy densities of 1090 and 818 kJ/kg in the 1st and 10th cycles, respectively. The cycling performance of the calcium-based composites under different light illumination conditions was compared with that using the TGA device. By comparing the optimal performance in two operating modes, the cycling stability of the calcium-based composites attenuated faster in the solar-driven fixed bed reactor than in the TGA device, which was ascribed to the uneven temperature distribution in the solar-driven reactor. By preventing surface overheating or localized hot spots in a direct solar-driven reactor, cycling stability of the calcium-based composites can be enhanced. Based on this principle, we propose some improvement methods for ensuring uniform temperature distribution in CaCO 3 -based composites during the direct solar-driven calcination process.
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