Ramesh T N, Kamath P Vishnu, Shivakumara C
Department of Chemistry, Central College, Bangalore University, Bangalore 560 001, India.
Acta Crystallogr B. 2006 Aug;62(Pt 4):530-6. doi: 10.1107/S0108768106013188. Epub 2006 Jul 12.
Nickel hydroxide samples obtained by strong alkali precipitation are replete with stacking faults. The local structures of the stacking faults resemble the stacking patterns of different polytypic modifications that are theoretically possible among the layered hydroxides. This resemblance becomes a basis for the classification of stacking faults into different types. Each type of stacking fault produces a characteristic non-uniform broadening of peaks in the X-ray powder diffraction pattern of nickel hydroxide. DIFFaX simulations aid the classification and quantification of stacking faults. Hydrothermal treatment of a poorly ordered nickel hydroxide slurry at different temperatures (338-473 K) and different durations (5-48 h) shows that the stacking faults are removed in a stepwise manner. The as-precipitated sample has 17-20% stacking faults of the 3R(2) variety, which evolve into the 2H(2) type at 413 K. The 2H(2) stacking faults persist up to 443 K. The stacking faults are completely removed only at 473 K. At this temperature an ordered beta-Ni(OH)(2) phase is observed.
通过强碱沉淀法获得的氢氧化镍样品充满了堆垛层错。堆垛层错的局部结构类似于层状氢氧化物中理论上可能存在的不同多型变体的堆积模式。这种相似性成为将堆垛层错分类为不同类型的基础。每种类型的堆垛层错都会在氢氧化镍的X射线粉末衍射图谱中产生特征性的峰非均匀展宽。DIFFaX模拟有助于堆垛层错的分类和定量。在不同温度（338 - 473 K）和不同持续时间（5 - 48 h）下对无序氢氧化镍浆料进行水热处理表明，堆垛层错是逐步消除的。沉淀后的样品具有17 - 20%的3R(2)型堆垛层错，在413 K时演变为2H(2)型。2H(2)堆垛层错一直持续到443 K。只有在473 K时堆垛层错才会完全消除。在此温度下观察到有序的β-Ni(OH)₂相。
