Controllable growth of perovskite structure oxide crystals with well-defined facets is challenging, especially in the mixed-valence state manganites with both rare-earth and alkaline-earth cations in their A-site. In this paper, we systematically studied the effects of the synthetic conditions of mineralizer concentration, reaction temperature and facet directing agent on the crystal shape formation of La_0.5Sr_0.5MnO₃. The shapes of single crystal La_0.5Sr_0.5MnO₃ have been controllably grown as cube, octahedron, rhombicuboctahedron and sphere by a high concentration KOH mineralized mild hydrothermal method with urea (CO(NH₂)₂) as crystal facet directing agent. The crystal growth mechanism for different facets has been analyzed according to Bravais−Friedel−Donnay−Harker theory. The as-grown facets for the different shapes of crystals indicate that the surfaces of La_0.5Sr_0.5MnO₃ are composed of {100}, {110} and {111} facets. Electrochemical cyclic and linear sweeping voltammetry measurement by rotating ring-disk electrode of these crystals indicates a facet-dependent process for oxygen reduction catalysis. This work provides a useful strategy for growing high index crystal facets of complex oxides and materials for crystal-facet dependent physico-chemical applications.

中文翻译：

---

La _0.5 Sr _0.5 MnO ₃晶体的水热形状可控合成及其对氧还原电子转移的刻面效应†

具有明确刻面的钙钛矿结构氧化物晶体的可控生长具有挑战性，特别是在A位同时具有稀土和碱土阳离子的混合价态锰矿中。在本文中，我们系统地研究了矿化剂浓度，反应温度和晶面定向剂的合成条件对La _0.5 Sr _0.5 MnO ₃晶体形貌的影响。通过尿素（CO（NH ₂）₂）的高浓度KOH矿化温和水热法，可控地生长了La _0.5 Sr _0.5 MnO ₃单晶形状为立方，八面体，菱形八面体和球形。）作为晶面导向剂。根据Bravais-Friedel-Donnay-Harker理论分析了不同晶面的晶体生长机理。不同晶体形状的生长小平面表明La _0.5 Sr _0.5 MnO ₃的表面由{100}，{110}和{111}小平面组成。通过旋转环盘电极对这些晶体进行电化学循环和线性扫描伏安法测量表明，氧还原催化是依赖于刻面的过程。这项工作为生长复杂氧化物和材料的高折射率晶体面提供了有用的策略，这些晶体和晶体依赖于物理化学应用。