Solid solutions of AlCl3 and TiCl3 were formed in all proportions by milling together dry powders of AlCl3 and TiCl3 (delta crystalline modification). For each composition, X-ray diffraction showed a single phase having a high degree of layer stacking disorder. These materials, including milled AlCl3, were isomorphous with the so-called delta modification of TiCl3.
The presence of solid solutions was investigated primarily by lattice parameter measurements made with a diffractometer and carried out with the aid of internal standards. For the milled materials, lattice parameter changes were observed not only with changes of composition, but also with the crystallite size. In terms of the system of hexagonal axes used for α TiCl3, the a parameter for the milled samples decreased with decreasing crystallite size, whereas the c parameter increased. In the samples examined, this effect was about the same order of magnitude as that due to changes in composition. In order to evaluate the effects due to composition alone, a correction was made for the effect of crystallite size, and the lattice parameters were then expressed as the limiting values one would obtain for very large crystals.
With increasing AlCl3 content, the a parameter decreased from 6.168 Å for no AlCl3 to 6.162 Å for 20 mol.% AlCl3. For higher AlCl3 content, a showed a relatively rapid and almost linear decrease to 5.921 Å for 100% Aids. The c parameter decreased from 17.73 Å for no AlCl3 to about 17.61 Å for 35 mol.% AlCl3, and thereafter decreased slowly to 17.58 Å for 100% AlCl3. The layer stacking disorder appeared to increase the lattice parameters in solid solutions containing less than 25 mol,% AlCl3. However, at 25% and 100% AlCl3, no significant effect was observed.