Charge and orbital order in frustrated Pb3Mn7O15

TL;DR

This study investigates the complex structural and electronic ordering phenomena in Pb3Mn7O15, revealing charge and orbital orderings that influence its magnetoelectric properties.

Contribution

It provides new insights into the charge and orbital ordering mechanisms in Pb3Mn7O15 using neutron and synchrotron X-ray diffraction.

Findings

Detection of large shifts in oxygen positions indicating charge ordering.

Identification of Mn3+ orbital ordering on ribbon sites.

Symmetry breaking linked to charge and orbital orderings.

Abstract

The candidate magnetoelectric Pb3Mn7O15 has a structure consisting of 1/3 filled Kagome layers linked by ribbons of edge-sharing octahedra in the stacking direction. Previous reports have indicated a complex hexagonal-orthorhombic structural transition upon cooling to room temperature, although its origins are uncertain. Here both structures are revisited using a combination of neutron and synchrotron X-ray diffraction data. Large shifts of oxygen positions are detected which show that the interlayer sites and those which occupy voids in the kagome lattice are trivially charge ordered in both phases. The symmetry breaking is found to occur due to Mn3+ orbital ordering on the ribbon sites and charge ordering of the sub-set of layer sites which make up a Kagome network.