The Intermetallic Semiconductor ht-IrGa₃: a Material in the in-Transformation State

Abstract

The compound IrGa3 was synthesized by direct reaction of the elements. It is formed as a high-temperature phase in the Ir-Ga system. Single-crystal X-ray diffraction analysis confirms the tetragonal symmetry (space group P42 /mnm, No. 136) with a = 6.4623(1) Å and c = 6.5688(2) Å and reveals strong disorder in the crystal structure, reflected in the huge values and anisotropy of the atomic displacement parameters. A model for the real crystal structure of ht-IrGa3 is derived by the split-position approach from the single-crystal X-ray diffraction data and confirmed by an atomic-resolution transmission electron microscopy study. Temperature-dependent electrical resistivity measurements evidence semiconductor behavior with a band gap of 30 meV. A thermoelectric characterization was performed for ht-IrGa3 and for the solid solution IrGa3–x Zn x .

Semiconducting and Metallic Compounds within the IrIn3 Structure Type: Stability and Chemical Bonding

“…Thus, the 17 e – narrow-gap semiconductors, RuGa 3 , OsGa 3 , and RuIn 3 , show zero COHP at the Fermi energy between the two sets of antibonding states, while for the 18 e – compounds, the Fermi level is located inside the conduction band, and the antibonding interactions are minimized at the Fermi energy. In fact, two pseudogaps and one real gap at the magic values of VEC = 15, 17, and 18 all demonstrate a stabilizing effect due to the minimization of antibonding d–p interactions, in agreement with the recent studies. , …”

“…In contrast to 18 e – CoGa 3 , CoIn 3 , RhIn 3 , and IrIn 3 , LT-IrGa 3 can be synthesized below 530 °C and crystallized in the Fe 3 C structure type with the expected metallic behavior . Remarkably, the high-temperature polymorph of IrGa 3 , which crystallizes in the title IrIn 3 structure type, demonstrates narrow-gap semiconducting behavior with the experimental band gap of 0.03 eV in agreement with the electronic-structure calculations . However, HT-IrGa 3 is metastable, and its behavior does not reflect equilibrium properties for this chemical composition …”

“…Remarkably, the high-temperature polymorph of IrGa 3 , which crystallizes in the title IrIn 3 structure type, demonstrates narrow-gap semiconducting behavior with the experimental band gap of 0.03 eV in agreement with the electronic-structure calculations . However, HT-IrGa 3 is metastable, and its behavior does not reflect equilibrium properties for this chemical composition …”

“…For these hypothetical IrIn 3 -type compounds, the semiconductor-like behavior is expected, too . Furthermore, a band gap opens at the Fermi energy in the case of IrGa 3 with VEC = 18 . These examples indicate that the chemical bonding involving d–p hybridization is flexible and may be adjusted for different values of VEC within the chosen structure type.…”

Superconductivity of structurally disordered Y5Ir6Sn18

“…Such a local disorder with domains breaking the average symmetry has been recently reported for numerous intermetallics ( e.g. Ba 7.81 Ge 40.67 Au 5.33 clathrate, 42 boron carbide, 43 β-Mg 2 Al 3 , 44 ht -IrGa 3 45 etc .). Theoretical calculations and simulations performed in these works also indicated the observed disorder to be an intrinsic property of such an intermetallic.…”