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Shape Controllable Synthesis of Bi-Based Perovskite Superconductor Microcrystals via a Mild Hydrothermal Method
journal contribution
posted on 2020-03-13, 21:17 authored by Shan Wang, Xin Wang, Long Yuan, Guangpeng Ma, Jiaqi Zhang, Yuan Zhang, Xiaoqiang Cui, Xiaofeng Wu, Dayong LuIn
this communication, we report two feasible routes to controllably
synthesize Bi-based perovskite structure superconductor crystals with
tunable shapes that expose well-defined crystal facets. The shape
of as-synthesized crystals is determined by the relative growing speed
along <001> and <111> crystallographic directions that
correlate
to the ratio of the propagation tendency of the A-O layer to BiO6 octahedral units. We have found two routes to control this
process by either decreasing the growing speed of the A-O layer (NH4+ route) or increasing that of the BO6 octahedral units (Bi(V)/Bi(III) route). The crystal growth and shape
formation mechanism were analyzed based on the E–pH
diagrams and crystal structure characteristics according to thermodynamic
data of the Bi–Ba–K–Na–H2O
system and the Bravais–Friedel–Donnay–Harker
(BFDH) theory. The temperature-dependent magnetization measurement
indicates that the diamagnetic and superconductive performance of
the samples is determined by the crystal shape and their exposed facets.
Truncated cubic shape crystals show the highest transition temperature
(∼30 K), while cubic shape crystals show the largest shielding
volume fraction (up to 49.2%). The increasing exposed ratio of {111}
facets on the surface of crystals reduces the shielding volume fraction.
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Keywords
shape formation mechanismBiO 6 octahedral unitscrystal structure characteristicstemperature-dependent magnetization measurementshape crystals showshape Controllable SynthesisBFDHNHBO 6 octahedral unitsA-O layerBi-based perovskite structure superconductor crystalsBi-Based Perovskite Superconductor MicrocrystalsMild Hydrothermal Methodshielding volume fraction
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