Lone Pair Effect, Structural Distortions and Potential for Superconductivity in Tl Perovskites

TL;DR

This study uses ab-initio calculations to explore Tl-based perovskites, revealing structural instabilities driven by lone pairs and potential for superconductivity similar to BaBiO3, especially upon hole doping.

Contribution

It identifies the structural and electronic properties of RbTlCl3 and related compounds, highlighting their potential as new superconductors with charge instability mechanisms.

Findings

Lone pair effects induce structural distortions in Tl perovskites.

Hole doping stabilizes structures without charge disproportionation.

RbTlCl3 shows electronic similarities to known superconductors.

Abstract

Drawing the analogy to BaBiO3, we investigate via ab-initio electronic structure calculations potential new superconductors of the type ATlX3 with A = Rb, Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. Based on chemical reasoning, supported by the calculations, we show that Tl-based perovskites have structural and charge instabilities driven by the lone pair effect, similar to the case of BaBiO3, effectively becoming A2Tl1+Tl3+X6. We find that upon hole doping of RbTlCl3, structures without Tl1+, Tl3+ charge disproportionation become more stable, although the ideal cubic perovskite, often viewed as the best host for superconductivity, should not be the most stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped RbTlCl3, predicted to be most stable in the same tetragonal structure, display highly analogous calculated electronic band structures.