Structural Investigation of BaIrO${}_3$ by Neutron Diffraction

Abstract

We report a temperature-dependent neutron diffraction (ND) study on polycrystalline monoclinic BaIrO${}_3$ which is famous for charge density wave (CDW) and weak ferromagnetic phase transitions at T${}_C$$\sim$180 K simultaneously. A Rietveld analysis on the ND patterns reveals that even though there is no symmetry breaking in crystal structure, a noticeable change in the four kinds of IrO${}_6$ octahedra is isolated as the temperature approaches to T${}_C$. Based on the structure analysis results, we calculated the $d$-orbital energy level splittings by crystal electric field for each type of the IrO${}_6$ octahedra. By taking into account the strong spin-orbit coupling in Ir 5$d$ orbitals and the lattice distortions obtained from the ND analysis, we propose an electronic configuration model to understand the phase transition of the system, where an effective $J_{\mathrm{eff},1/2}$ Mott insulating phase and a charge gap phase induced by bonding states between the $J_{\mathrm{eff},1/2}$ states compete each other.

To appear in Journal of the Korean Physical Society