The temperature dependence of the coefficient of thermal expansion of the II-IV-V2 compounds is, apparently, similar to that of the elemental and binary adamantine substances; namely, it is negative at low temperatures. The electronic structure of II-IV-V2 differs from that of III-V compounds as a consequence of the presence of two sorts of atoms in the cation sublattice of the ternary compounds, distortion of the “adamantine” tetrahedrons in the lattice, and increase of the unit cell volume. Consequently, any combination of elemental, binary, or ternary substances that belong to the adamantine family with a binary defect phase will be a phase (a compound, an ordered or disordered solid solution, etc.) that also belongs to the same family. Numerous attempts to synthesize compounds consisting of heavier elements have shown that many of the prepared alloys are unstable and often contain noticeable amounts of free elemental components in the products of synthesis.