The principle of “derivative structures” in solid-state chemistry, with examples relevant to electronic materials. (Top) The familiar salt and diamond structures (the latter describing silicon) are themselves derived from the simpler face-centered cubic (fcc) structure. (Middle) The III-V crystal structure of GaAs derives from Si by placing different atoms in the fcc and tetrahedral positions, and the LiZnAs structure (describing several small-band-gap thermoelectrics) derives from NaCl by filling half of the tetrahedral voids. (Bottom) The CuInSe2 structure of semiconductors used in photovoltaic cells is derived from GaAs by replacing Ga with an ordered arrangement of Cu and In and the structure of MnCu2Sn (important for half metallic ferromagnets and superconductors) is derived from the LiZnAs structure by filling the remainder of the tetrahedral voids. Finally, LiMnAs (Jungwirth et al.) can be derived from either GaAs or LiZnAs. At every step in the derivative pathway, the added chemical degrees of freedom offer more means to tune the electronic properties.