Two-dimensional (2D) lead-free (K, Na)NbO₃ (KNN) micro/nano structures with controllable K/Na ratio were successfully fabricated via a two-step molten salt synthesis (MSS). In this work, the reaction factors, including the proportion of molten salts, the types of carbonates, the sintering temperature, and the sintering time, were discussed in detail and the optimized condition was identified. The microstructure of KNN was confirmed by confocal Raman spectroscopy, while piezoresponse force microscopy (PFM) was applied to measure three-dimensional (3D) morphology and piezoelectric properties of KNN particles. The as-synthesized KNN platelets apparently possess anisotropic morphology and uniform structure, the size of which reaches 5–20 µm in length/width and 0.5–1 µm in thickness. It should be noted that the K/Na ratios of the KNN crystals are basically consistent while the proportion of salts changes within a certain range. The enrichment of Na element in the products is also observed, which owes to the smaller ionic radius of Na+ comparing to that of K+. This result provides a reference for the further preparation of textured ceramics and flexible piezoelectric generators.

中文翻译：

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二维无铅（K，Na）NbO 3微米/纳米压电结构的合成与表征

二维（2D）无铅（K，Na）NbO ₃通过两步熔融盐合成（MSS）成功地制造了具有可控K / Na比的（KNN）微/纳米结构。在这项工作中，详细讨论了反应因素，包括熔融盐的比例，碳酸盐的类型，烧结温度和烧结时间，并确定了最佳条件。共焦拉曼光谱证实了KNN的微观结构，而压电响应力显微镜（PFM）用于测量KNN粒子的三维（3D）形态和压电性能。合成后的KNN血小板显然具有各向异性的形态和均匀的结构，其大小的长/宽达到5–20 µm，厚度达到0.5–1 µm。应该注意的是，当盐的比例在一定范围内变化时，KNN晶体的K / Na比值基本一致。还观察到产物中Na元素的富集，这是由于Na +的离子半径小于K +的离子半径。该结果为进一步制备网纹陶瓷和柔性压电发电机提供参考。