K_xCoO_2·yH_2O(x<0.2,y≤0.8)的晶体结构、输运及磁学性质

Structural, transport and magnetic properties of K_xCoO_2·yH_2O(x<0.2, y≤0.8)

利用熔融KOH和Co3O4在较低温度(480℃)下反应制备出K0.36CoO2,然后用高锰酸钾溶液和饱和的过硫酸钾溶液进行氧化处理.氧化的同时伴随有水分子嵌入.K0.36CoO2用高锰酸钾和过硫酸钾溶液处理后分别得到K0.12CoO2.0.8H2O和K0.16CoO2.0.6H2O.这两种化合物都属于六角晶系,表现出金属行为,脱水后主相变为正交结构并且呈现出半导体特性.K0.16CoO2.0.6H2O在56K附近可能存在自旋玻璃转变行为或其他涨落.随着钾含量的减少和水含量的增多,样品的自旋玻璃行为受到抑制或发生磁性相分离.样品K0.12CoO2.0.8H2O在零场冷却和有场冷却曲线上的分叉现象基本上消失.还讨论了产生KxCoO2与NaxCoO2体系结构和物性差别的原因.

Layered potassium cobaltate K0.36 CoO2 has been successfully synthesized from KOH fluxes at 480 ℃ . The K0.36 CoO2 sample can be oxidized and intercalated with water by treatment in KMnO4 and K2S2O8 solutions. K0.12CoO2 ·0.8H2O and Ko0.16CoO2·0.6H2O have been obtained after the KMnO4 and K2S2O8 treatment, respectively. The diffraction peaks of K0.12CoO2·0.8H2O and K0.16CoO2 ·0.6H2O can be well indexed by a hexagonal cell similar to the monolayer hydrate NaxCoO2·yH2O. After dehydration, the major phases have an orthorhombic structure similar to Na0.5 CoO2 and show semiconductor behavior. Both K0.12CoO2·0.8H2O and K0.16CoO2·0.6H2O are primarily paramagnetic and show metallic behavior. K0.16CoO2 ·0.6H2O has a spin-glass-like transition or other magnetic fluctuations around 56 K. The spin-glass-like transition or the regions of magnetic phase separation are reduced in K0.12 CoO2·0. 8H2O due to the increasing of the intercalated water. We also discussed similarities and differences between the structural and physical properties of Kx CoO2 and NaxCoO2.