Raman-scattering and x-ray-scattering experiments have been performed on the mixed-alkali-halide systems $\mathrm{K}{\mathrm{Br}}_{1\ensuremath{-}x}{\mathrm{I}}_{x}$, $\mathrm{K}{\mathrm{Cl}}_{1\ensuremath{-}x}{\mathrm{I}}_{x}$, and ${\mathrm{K}}_{1\ensuremath{-}x}{\mathrm{Rb}}_{x}\mathrm{Cl}$, and the results have been compared with our earlier work on the $\mathrm{K}{\mathrm{Cl}}_{1\ensuremath{-}x}{\mathrm{Br}}_{x}$ system. Both powder-pattern and line-broadening studies have been carried out using x-ray scattering. Our earlier work on $\mathrm{K}{\mathrm{Cl}}_{1\ensuremath{-}x}{\mathrm{Br}}_{x}$ has been reevaluated and the previous lower limit of a few hundred angstroms for cluster sizes has been raised to 4000 \AA{}. The $\mathrm{K}{\mathrm{Br}}_{1\ensuremath{-}x}{\mathrm{I}}_{x}$ system has been seen to display several different microscopic structures. For $x>0.7$ the bulk crystals were seen to have the x-ray properties of bulk crystals. For $x<0.1$, the bulk crystals were seen to be composed of crystallites a few hundred angstroms in size. For $0.7\ensuremath{\ge}x\ensuremath{\ge}0.1$, the bulk crystals were found to consist of three distinct phases, occuring in crystallites ranging in size from 300 to 1650 \AA{}. Raman spectra for $\mathrm{K}{\mathrm{Br}}_{1\ensuremath{-}x}{\mathrm{I}}_{x}$ in the ranges $x<0.1$ and $x>0.7$ and for $\mathrm{K}{\mathrm{Cl}}_{1\ensuremath{-}x}{\mathrm{I}}_{x}$ were seen to be of ${A}_{1g}$ and ${T}_{2g}$ symmetry and showed the same systematic behavior as the $\mathrm{K}{\mathrm{Cl}}_{1\ensuremath{-}x}{\mathrm{Br}}_{x}$ system reported earlier. That is, certain spectral features could apparently be identified with particular zone-boundary phonons of the mixed crystal and the variation of frequency of these phonons as a function of concentration $x$ could be studied. The variation was seen to be linear. Similar results were seen to pertain for ${\mathrm{K}}_{1\ensuremath{-}x}{\mathrm{Rb}}_{x}\mathrm{Cl}$, except that the mixed-crystal spectra were of ${E}_{g}$ and ${T}_{2g}$ symmetry. However, it is also suggested that the Raman results may merely be a reflection of the fact that the zone-boundary phonons observed also happen to correspond to the peaks in the phonon density of states.