We present a structural analysis of two metal hexaboride solid solutions. The powders were synthesized by solution combustion synthesis, acid-washed with HCl, and characterized by X-ray diffraction (XRD), inductively coupled plasma mass spectrometry (ICP-MS), selected-area electron diffraction (SAED) and transmission and scanning electron microscopies (TEM and SEM). XRD proves a high crystallinity of the prepared powders and SEM demonstrates cubic morphologies. For identification of the concentration of dopants, ICP-MS on the dissolved powders was performed, showing a concentration of 1 to 3 at.%. Both SAED and TEM studies show a monocrystalline growth of the cubes in the [100] direction, and a constant lattice parameter. Together, these studies will contribute to the understanding of hexaboride properties tailoring for neutron detection applications.