Structural Characterization of Synthetic Hydrotalcite-like [Mg_1-xGa_x(OH)₂](CO₃)_x/2·mH₂O

A series of Ga-substituted hydrotalcite-like compounds, [Mg_1-xGa_x(OH)₂] (CO₃)_x/2·mH₂O (where 0.07 ≤ x ≤ 0.36; GaHTs), were obtained in order to characterize their structural and crystal properties by means of X-ray diffraction and conventional/high-resolution electron microscopy. A linear relationship between Mg/Ga ratios and the a parameter (3.123−3.086 Å) was found for all x values, indicating that Ga³⁺ cations incorporate into the layered structure. The interlayer spacing, i.e. the c parameter, shrinks (8.173−7.574 Å) as the Ga content increases, due to a greater electrostatic attraction between layers and interlayers. However, for Ga-poor materials (Mg/Ga = 7.7, 12.9) the c parameter remains practically constant (8.173 and 8.169 Å), probably due to the high dilution of Ga in the brucite-like layers. GaHTs are made up of hexagonal crystallites. High-resolution observations of the layered stacking structure point out a defective configuration containing dislocations, stacking faults, weaving planes, and disruptions in planes. Outermost layers in a crystal plate present interlayer distances (3.0−3.8 Å) greater than those in the bulk (2.4 Å), suggesting that peripheral layers are probably more loosely bonded to each other than the later ones.