Small Co₃O₄ cubes and cuboctahedra were synthesized at 110 and 150 °C in just 2 h, respectively. Size-tunable nanocubes were also prepared at 150 °C for 2 h. Despite their high crystalline quality as seen from X-ray and electron diffraction patterns, cubes and cuboctahedra formed at 150 °C present clear lattice deviations, while cubes synthesized at 110 °C show crystal perfection. Large amounts of Co₃O₄ cubes, octahedra, cuboctahedra, and truncated octahedra can also be obtained. These Co₃O₄ crystals exhibit both size- and facet-dependent absorption positions and band gaps. Remarkably, while smaller magnetization differences can be identified at 300 K, octahedra become much more magnetized than cubes and cuboctahedra at 2 K. Their Néel temperatures also vary. Octahedra have notably larger coercivity and retentivity values than cubes and cuboctahedra at 2 K. Thus, in addition to various facet-dependent properties of semiconductor materials, magnetic behaviors also reveal surface effects. This means that there is the potential to prepare more powerful magnets through surface control.

中文翻译：

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具有表面依赖性光学和磁性特性的形状可调 Co3O4 纳米晶体

小Co ₃ O ₄立方体和立方八面体分别在110 和150 °C 下仅用2 小时合成。还在 150°C 下制备了尺寸可调的纳米立方体 2 小时。尽管从 X 射线和电子衍射图可以看出，立方体和立方八面体具有很高的结晶质量，但在 150 °C 下形成的立方体和立方八面体呈现出明显的晶格偏差，而在 110 °C 下合成的立方体则显示出完美的晶体。还可以获得大量的Co ₃ O _{4立方体、八面体、立方八面体和截角八面体。}这些Co ₃ O ₄晶体表现出尺寸和晶面相关的吸收位置和带隙。值得注意的是，虽然在 300 K 时可以识别出较小的磁化强度差异，但在 2 K 时八面体的磁化强度比立方体和立方八面体强得多。它们的尼尔温度也有所不同。在 2 K 下，八面体比立方体和立方八面体具有明显更大的矫顽力和保持力值。因此，除了半导体材料的各种依赖于面的特性之外，磁性行为还揭示了表面效应。这意味着有可能通过表面控制来制备更强大的磁体。