Novel Charge Ordering in the Trimer Iridium Oxide BaIrO3

TL;DR

This paper investigates the phase transition in BaIrO3, revealing a charge ordering phenomenon in a Mott insulator with face-shared Ir3O12 trimers, using experimental measurements and an electronic model.

Contribution

It introduces a new electronic model explaining the transition as a Mott insulator to charge ordered insulator in BaIrO3.

Findings

BaIrO3 is a Mott insulator with face-shared Ir3O12 trimers.

The phase transition at 182 K involves charge ordering.

Synchrotron x-ray diffraction supports the proposed charge order.

Abstract

We have prepared polycrystalline samples of the trimer Ir oxide BaIrO3 with face-shared Ir3O12 trimers, and have investigated the origin of the phase transition at 182 K by measuring resistivity, thermopower, magnetization and synchrotron x-ray diffraction. We propose a possible electronic model and transition mechanism, starting from a localized electron picture on the basis of the Rietveld refinement. Within this model, BaIrO3 can be basically regarded as a Mott insulator, when the Ir3O12 trimer is identified to one pseudo-atom or one lattice site. The transition can be viewed as a transition from the Mott insulator phase to a kind of charge ordered insulator phase.