In 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.

中文翻译：

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轻度水热法可控地合成双基钙钛矿超导体微晶

在本交流中，我们报告了两条可行的途径，以可控制的方式可控制地合成具有可调谐形状的Bi基钙钛矿结构超导体晶体，这些晶体可暴露出明确定义的晶体面。合成晶体的形状由沿<001>和<111>晶体学方向的相对生长速度决定，该速度与AO层与BiO ₆八面体单元的传播趋势之比相关。我们发现有两种途径可通过降低AO层的生长速度（NH ₄ ⁺途径）或提高BO ₆八面体单元的生长速度（Bi（V）/ Bi（III）途径）来控制该过程。基于E分析了晶体的生长和形状形成机理– Bi–Ba–K–Na–H ₂ O系统的热力学数据和Bravais–Friedel–Donnay–Harker（BFDH）理论的–pH图和晶体结构特征。随温度变化的磁化强度测量表明，样品的抗磁和超导性能取决于晶体形状及其裸露面。截断的立方晶体显示最高的转变温度（约30 K），而立方晶体显示最大的屏蔽体积分数（高达49.2％）。晶体表面上{111}晶面暴露率的增加降低了屏蔽体积分数。