This study investigates the hydrothermal synthesis of KNbO-NaNbO particles, which contains compositions of interest as lead-free piezoelectric materials. Precursor solutions containing NbO, NaOH/KOH were hydrothermally reacted at 190 C for 15 hours using either a conventional reactor or a reactor with stirring. For 50 % KOH or lower, the product was cubic or elongated cuboid/belt-shaped NaNbO, whereas solely KOH resulted in hexagonal plate-like KNbO. When 75 % KOH was used, the product was a mixture of large KNaNbO·9 HO hexagonal plates and smaller NaNbO cubes. We hypothesized this phase segregation was induced by highly concentrated microenvironments, and stirring would prevent that. Accordingly, stirring hydrothermal treatment of 75 % KOH solution produced only KNaNbO·HO hexagonal plates, which could be transformed to KNaNbO by calcination. By reducing the hydrothermal treatment time to 1 – 6 hours we isolated reaction intermediates, and based on them propose a kinetics-controlled mechanism for hydrothermal reactions of NbO and KOH/NaOH.

中文翻译：

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搅拌和KOH/NaOH比对水热合成KNbO3-NaNbO3颗粒相形成的影响


本研究研究了 KNbO-NaNbO 颗粒的水热合成，其中包含作为无铅压电材料的感兴趣的成分。使用常规反应器或搅拌反应器将含有NbO、NaOH/KOH的前体溶液在190℃下水热反应15小时。对于 50% 或更低的 KOH，产物为立方体或细长的长方体/带状 NaNbO，而仅使用 KOH 则产生六方板状 KNbO。当使用 75% KOH 时，产物是大的 KNaNbO·9 H2O 六角板和较小的 NaNbO 立方体的混合物。我们假设这种相分离是由高度浓缩的微环境引起的，而搅拌可以防止这种情况发生。因此，对75% KOH溶液进行搅拌水热处理仅生成KNaNbO·HO六方片，通过煅烧可将其转化为KNaNbO。通过将水热处理时间缩短至 1 – 6 小时，我们分离出了反应中间体，并在此基础上提出了 NbO 和 KOH/NaOH 水热反应的动力学控制机制。