Crystalline intermetallic compounds in the K-Te system: The Zintl-Klemm principle revisited

We have investigated the crystal structure, chemical bonding, and electronic properties of all known intermetallic compounds in the K-Te system, employing a first-principles local-density-functional approach including generalized gradient corrections. The structural parameters, such as equilibrium volume, lattice constants, and internal parameters are in very good agreement with experiment. The evaluation of the total and angular-momentum decomposed densities of states (DOS) and the partial charge densities gives further insight into the bonding properties of these solids. Our results confirm the validity of the Zintl-Klemm principle for the saltlike compound K2Te and for the two equiatomic phases α-K2Te2 and β-K2Te2 consisting of isolated K ions and covalently bounded Te2 dimers. In the compound K5Te3 ionic regions consisting of K+ and Te2- ions with closed octet shells and polyanionic regions with an atomic arrangement dominated by Te22- dianions coexist in the crystal lattice. In the electron-deficient-compound K2Te3, larger polyanions-Te32- trimers-have to be formed to achieve saturated covalent bonds. Our results illustrate the validity and astonishing flexibility of the Zintl-Klemm principle, which allows us to interpret all crystal structures in the K-Te system, from the saltlike octet compound to the Te-rich phases with extended polyanionic superstructures, on a common footing.