Tl2Ir2O7: A Pauli Paramagnetic Metal, Proximal to a Metal Insulator Transition

A polycrystalline sample of Tl2Ir2O7 was synthesized by high-pressure and high-temperature methods. Tl2Ir2O7 crystallizes in the cubic pyrochlore structure with space group Fd (3) over barm (No. 227). The Ir4+ oxidation state is confirmed by Ir-L-3 X-ray absorption near-edge spectroscopy. Combined temperature-dependent magnetic susceptibility, resistivity, specific heat, and DFT+DMFT calculation data show that Tl2Ir2O7 is a Pauli paramagnetic metal, but it is close to a metal-insulator transition. The effective ionic size of Tl3+ is much smaller than that of Pr3+ in metallic Pr2Ir2O7; hence, Tl2Ir2O7 would be expected to be insulating according to the established phase diagram of the pyrochlore iridate compounds, A(2)(3+)Ir(2)(4+)O(7). Our experimental and theoretical studies indicate that Tl2Ir2O7 is uniquely different from the current A(2)(3+)Ir(2)(4+)O(7) phase diagram. This uniqueness is attributed primarily to the electronic configuration difference between Tl3+ and rare-earth ions, which plays a substantial role in determining the Ir-O-Ir bond angle, and the corresponding electrical and magnetic properties.

Automated summary

Tl2Ir2O7 is a Pauli paramagnetic metal that is close to a metal-insulator transition, with unique properties attributed to the electronic configuration difference between Tl3+ and rare-earth ions.