OXIDATION-STATES, TRANSPORT-PROPERTIES, AND TE-CENTER-DOT-CENTER-DOT-CENTER-DOT-TE SHORT CONTACTS IN THE TERNARY TRANSITION-METAL TELLURIDES TA3PD3TE14 AND TA4PD3TE16

The electronic structures of the layered ternary tellurides Ta3Pd3Te14 and Ta4Pd3Te16 are examined. It is found that the presence of bicappe d trigonal prismatic chains with extensive Te ... Te interactions resu lts in very wide tellurium-based bands along the direction of the chai ns. The local octahedral coordination of the Pd and one type of Ta ato ms, as well as additional short Te ... Te contacts, allows for the par ticipation of the remaining chains of the layer in such a delocalizati on. This leads to large tellurium to metal electron transfers and diff iculties in proposing meaningful oxidation states for the Pd and Ta at oms. The interlayer Te ... Te interactions are found to exert a strong control of the density of states at the Fermi level and, hence, of th e conductivity of these phases. The results are also compared with tho se for Ta3SiTe6, a structurally different layered ternary telluride wi th short Te ... Te contacts. For this phase, meaningful oxidation stat es for the Ta and Si atoms can be proposed. The different, but importa nt, role of interlayer Te ... Te interactions in Ta3SiTe6 is also disc ussed.