Compounds with the Ir3Ge7 Structure Type: Interpenetrating Frameworks with Flexible Bonding Properties

Abstract

Reexamination of the E-rich (E Ga, In) area of the binary systems Ni/Ga and Pd/In yielded the stoichiometric compounds Ni 3 Ga 7 and Pd 3 In 7 with the Ir 3 Ge 7 structure type. The structure of the compounds was determined by single-crystal X-ray diffraction methods (space group Im3 Å m; Ni 3 Ga 7 : a 8.4285(6) , Pd 3 In 7 : a 9.4323(2) ; Z 4). The existence of the nonstoichiometric phases NiGa 4 and PdIn 3 reported earlier could not be confirmed and it is assumed that Ni 3 Ga 7 and Pd 3 In 7 represent the most E-rich compounds in their respective systems. The remarkable Ir 3 Ge 7 structure consists of two equivalent interpenetrating frameworks built from cubes and square antiprisms. Its chemical bonding motifs were analysed by ab initio linear muffin-tin orbital (LMTO) and semiempirical tight-binding extended Hückel band-structure calculations. It was found that the valence electron concentration plays a crucial role in the structural stability of the Ir 3 Ge 7 type and that, in the case of strong dp bonding between transition metal and E component, semiconducting representatives can occur. We suggest that the width of the band gaps is tunable by the choice of constituent elements in ternary and quarternary compounds with the Ir 3 Ge 7 structure.

Electronic Band Structure of Ru3Sn7

“…1 [7]. Below E F there is a rich structure but one recognizes two main regions, one spans just below E F down to 0.3 Ry, and the second region is located around 0.55 Ry, relative to E F .…”

“…Similarities and dierences between DOS of these compounds will be discussed in terms of their electronic and magnetic behaviour. Previously, a large number of theoretical investigations were dedicated to Mo 3 Sb 7 [58], while study on Ru 3 Sn 7 was reported only by Häussermann et al [7], who obtained from ab initio linear mun-tin orbital method in the atomic sphere approximation (ASA) calculations.…”

Chemical aspects of the design of thermoelectric materials

“…This is associated with a gap opened in the band structure, which separates the bonding and antibonding d ± pinteractions T7E. 150 Thus Nb 3 Sb 2 Te 5 and Mo 3 Sb 77x Te x (x & 2) exhibit semiconductor properties. Minor deviations from 55 are possible; in this case, the required concentration of charge carriers is achieved, thus optimising the thermoelectric properties.…”

Optimized thermoelectric properties of Mo3Sb7−xTex with significant phonon scattering by electrons

“…[16][17][18][19][20][21] The matrix compound Mo 3 Sb 7 exhibits strong p-type metallic behavior because the Fermi level locates deep into the valence band. The effective way to optimize the electrical performance is to move the Fermi level towards the valence band maximum, which means more electrons are needed for this compound.…”