Departamento de Química Inorgánica I, Facultad de Químicas, Universidad Complutense de Madrid, 28040, Madrid, Spain.
Dalton Trans. 2012 Feb 14;41(6):1840-7. doi: 10.1039/c1dt11558h. Epub 2011 Dec 14.
The half-metallic ferromagnet K(2)Cr(8)O(16) with the hollandite structure has been chemically modified using soft chemistry methods to increase the average oxidation state of chromium. The synthesis of the parent material has been performed under high pressure/high temperature conditions. Following this, different redox reactions have been carried out on K(2)Cr(8)O(16). Oxidation to obtain potassium-de-inserted derivatives, K(2-x)Cr(8)O(16) (0 ≤x≤ 1), has been investigated with electrochemical methods, while the synthesis of sizeable amounts was achieved chemically by using nitrosonium tetrafluoroborate as a highly oxidizing agent. The maximum amount of extracted K ions corresponds to x = 0.8. Upon oxidation the hollandite structure is maintained and the products keep high crystallinity. The de-insertion of potassium changes the Cr(3+)/Cr(4+) ratio, and therefore the magnetic properties. Interestingly, the Curie temperature increases from ca. 175 K to 250 K, getting therefore closer to room temperature.
具有霍兰德石结构的半金属铁磁体 K(2)Cr(8)O(16) 已通过软化学方法进行化学修饰，以提高铬的平均氧化态。母体材料的合成是在高压/高温条件下进行的。在此之后，对 K(2)Cr(8)O(16) 进行了不同的氧化还原反应。通过电化学方法研究了氧化以获得钾脱插衍生物 K(2-x)Cr(8)O(16)（0 ≤x≤ 1），而通过使用四氟硝鎓作为强氧化剂，通过化学方法合成了大量的产物。最大量的提取 K 离子对应于 x = 0.8。氧化时，霍兰德石结构得以保持，产物保持高结晶度。钾的脱插改变了 Cr(3+)/Cr(4+)的比值，从而改变了磁性。有趣的是，居里温度从约 175 K 增加到 250 K，因此更接近室温。
