We study an A(1-x)B(x) alloy on a two-dimensional triangular lattice. The i
ons A and B have different charges, with a background charge to ensure neut
rality, and an constrained to lie at the discrete sites defined by a fixed
triangular lattice. We study the various structures formed at different com
positions x by doing computer simulations to find the lowest energy, using
an energy minimization scheme, together with simulated annealing. Like ions
try to avoid each other because of charge repulsion, which leads to struct
ures, which are very different from those in a random alloy. At low concent
rations, a triangular Wigner lattice is formed, which evolves continuously
up to a concentration of x = 1/3. For higher concentrations, 1/3 less than
or equal to x less than or equal to 1/2 there are long polymer chains, with
occasional branches. We show that there is a symmetry about x = 1/2, which
is the percolation point for nearest neighbors on the triangular lattice.
At certain special stoichiometries, regular superlattices are formed, which
usually have a slightly lower energy than a disordered configuration. The
powder-diffraction patterns are calculated. The magnetic properties of this
structure are also studied, and it is shown that the high-temperature susc
eptibility could be a useful diagnostic tool, in that it is very sensitive
to the number of nearest-neighbor magnetic pairs. This work contributes to
a better understanding of layered double hydroxides like Ni1-xAlx(OH)(2)(CO
3)(x/2). yH(2)O. [S0163-1829(99)12001-0].