Bond versus charge disproportionation and nature of the holes in s−p ABX3 perovskites

Abstract

We use density functional theory methods to study the electronic structures of a series of $s\text{\ensuremath{-}}p$ cubic perovskites, $AB{X}_{3}$: the experimentally available $\mathrm{Sr}\mathrm{Bi}{\mathrm{O}}_{3}, \mathrm{Ba}\mathrm{Bi}{\mathrm{O}}_{3}, \mathrm{Ba}\mathrm{Sb}{\mathrm{O}}_{3}, \mathrm{Cs}\mathrm{Tl}{\mathrm{F}}_{3}$, and $\mathrm{Cs}\mathrm{Tl}{\mathrm{Cl}}_{3}$, as well as the hypothetical $\mathrm{Mg}{\mathrm{PO}}_{3}, \mathrm{Ca}\mathrm{As}{\mathrm{O}}_{3}, \mathrm{Sr}\mathrm{Sb}{\mathrm{O}}_{3}$, and $\mathrm{Ra}\mathrm{Mc}{\mathrm{O}}_{3}$. We use tight-binding modeling to calculate the interatomic hopping integrals ${t}_{sp\ensuremath{\sigma}}$ between the $B\phantom{\rule{4pt}{0ex}}s$ and $X\phantom{\rule{4pt}{0ex}}p$ atomic orbitals and charge-transfer energies $\mathrm{\ensuremath{\Delta}}$, which are the two most important parameters that determine the low-energy electron and hole states of these systems. Our calculations elucidate several trends in ${t}_{sp\ensuremath{\sigma}}$ and $\mathrm{\ensuremath{\Delta}}$ as one moves across the periodic table, such as the relativistic energy lowering of the $B\phantom{\rule{4pt}{0ex}}s$ orbital in heavy $B$ cations, leading to strongly negative $\mathrm{\ensuremath{\Delta}}$ values. Our results are discussed in connection with the general phase diagram for $s\text{\ensuremath{-}}p$ cubic perovskites proposed by Khazraie et al. [Phys. Rev. B 98, 205104 (2018)], who find the parent superconductors $\mathrm{Sr}\mathrm{Bi}{\mathrm{O}}_{3}$ and $\mathrm{Ba}\mathrm{Bi}{\mathrm{O}}_{3}$ to be in the regime of negative $\mathrm{\ensuremath{\Delta}}$ and large ${t}_{sp\ensuremath{\sigma}}$. Here, we explore this further and search for different materials with similar parameters, which could lead to the discovery of new superconductors. Also, some considerations are offered regarding a possible relation between the physical properties of a given $s\text{\ensuremath{-}}p$ compound (such as its tendency to bond disproportionate and the maximal achievable superconducting transition temperature) and its electronic structure.