Classification of stacking faults and their stepwise elimination during the disorder→order transformation of nickel hydroxide

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.