Linear tetramer formation in nonmagnetic pyrochlore niobate

TL;DR

This study reveals that in nonmagnetic pyrochlore Y2Nb2O7, local Nb displacements form linear tetramers, which are crucial for understanding its insulating state, using synchrotron X-ray diffraction and RMC simulations.

Contribution

It uncovers the formation of linear Nb4 tetramers through local displacements, highlighting the role of molecular orbitals in stabilizing the nonmagnetic insulating state.

Findings

Identification of characteristic diffuse scattering pattern

Discovery of Nb displacements along <111> axes

Formation of linear Nb4 tetramers

Abstract

We investigate displacive short-range order in pyrochlore Y2Nb2O7, which exhibits a nonmagnetic insulating state despite the presence of formally tetravalent Nb4+ (S = 1/2) ions on the pyrochlore network. Synchrotron x-ray diffraction on a single crystal reveals a characteristic x-ray diffuse scattering (XDS) pattern primarily around q = {0.5, 0.5, 2}. Reverse Monte Carlo (RMC) simulations uncover local Nb displacements along the <111> axes, leading to the formation of linear Nb4 tetramers. Our findings highlight a crucial role of molecular orbital degrees of freedom in stabilizing the nonmagnetic insulating state. This study demonstrates that RMC analysis of XDS provides a powerful approach for elucidating short-range correlations and the underlying mechanisms governing the physical properties of crystalline materials.