Polymorphism and Structural Disorder in the Carbonate Containing Layered Double Hydroxide of Li with Al

The carbonate containing layered double hydroxide (LDH) of Li with Al having the formula [LiAl₂(OH)₆](CO₃)_0.5·1.5H₂O crystallizes in the monoclinic system. The single layered cell belongs to the 1M polytype. However, the crystallites are extensively faulted. The structural disorder is on account of the incorporation of stacking faults. The stacking faults cause the nonuniform broadening of peaks due to the hkl reflections in the powder X-ray diffraction pattern. Using DIFFaX simulations, we compare the local structure of the stacking faults with the structure of the different theoretically possible polytypes within the monoclinic crystal system. Such a comparison shows that the stacking faults arise due to the random incorporation of motifs having orthorhombic symmetry (2O polytype) within the matrix of monoclinic symmetry. On heating, the progressive dehydration of the interlayer region introduces turbostratic disorder. This is in contrast with the case of halide containing LDHs, which exhibit an ordering of the interlayer upon dehydration.