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

Abstract

A polycrystalline sample of Tl 2 Ir 2 O 7 was synthesized by high-pressure and high-temperature methods. Tl 2 Ir 2 O 7 crystallizes in the cubic pyrochlore structure with space group Fd3̅ m (No. 227). The Ir 4+ oxidation state is confirmed by Ir−L 3 Xray absorption near-edge spectroscopy. Combined temperaturedependent magnetic susceptibility, resistivity, specific heat, and DFT+DMFT calculation data show that Tl 2 Ir 2 O 7 is a Pauli paramagnetic metal, but it is close to a metal−insulator transition. The effective ionic size of Tl 3+ is much smaller than that of Pr 3+ in metallic Pr 2 Ir 2 O 7 ; hence, Tl 2 Ir 2 O 7 would be expected to be insulating according to the established phase diagram of the pyrochlore iridate compounds, A 3+ 2 Ir 4+ 2 O 7 . Our experimental and theoretical studies indicate that Tl 2 Ir 2 O 7 is uniquely different from the current A 3+2 Ir 4+ 2 O 7 phase diagram. This uniqueness is attributed primarily to the electronic configuration difference between Tl 3+ and rare-earth ions, which plays a substantial role in determining the Ir−O−Ir bond angle, and the corresponding electrical and magnetic properties.

Anomalous metallic conductivity and short-range ferromagnetic correlation in high-pressure synthesized pyrochlore

“…The resistivity shows a steady decrease with decreasing temperature from 300 to 100 K, where the magnetization is almost a constant coincidentally. With decreasing temperature, the resistivity gradually decrease above 100 K. Similar metallic conduction was found in RE 2 Ir 2 O 7 , with well-defined Ir 4+ [7,38,39]. Thus, the metallic conduction can also distinguish Hg 2 Ir 2 O 7 from the J = 0 state.…”

Effect of Post-Annealing on Magnetotransport and Magnetic Properties of TaCo2Te2 Single Crystals

“…This minimum behavior on the M(T) curve is a rather abnormal behavior and is similar to that in the literature. 14 This shallow minimum on the M(T) curve has been observed in SrIrO 3 , 31 BaFe 2 As 2 , 32 Tl 2 Ir 2 O 7 , 33 BaIrO 3 , 34 BaRuO 3 , 35 etc. This minimum phenomenon is a complicated behavior, and the relevant explanations are few.…”

Characterization of a Dynamic Y2Ir2O7 Catalyst during the Oxygen Evolution Reaction in Acid

“…This distinctive peak shape measured by HERFD-XAS is attributed to the different electronic configuration of Ir in Y 2 Ir 2 O 7 , where electron correlations and spin–orbit coupling are known to split the Ir 5d t 2g orbital into e″ and u′ orbitals, ,,, whereas all five d valence electrons in IrO 2 occupy the t 2g orbital that spans the Fermi level, the d electrons in Y 2 Ir 2 O 7 fill the u′ orbital and half-fill the higher energy e″ orbital with localized empty states above the Fermi level. , In addition, the intensity of the low energy shoulder feature in the white line strongly depends on the number of holes in the t 2g states, which is greater for Y 2 Ir 2 O 7 than IrO 2 as evidenced by the white line position (Figure C) and the XPS results (Figure S5). In other words, the double feature we observed is due to the gap in t 2g states and the high oxidation state of Ir.…”