Valency of rare earths in RIn3 and RSn3: Ab initio analysis of electric-field gradients

TL;DR

This paper revisits the valency of rare earth elements in RIn3 and RSn3 compounds using ab initio calculations of electric-field gradients, providing a more reliable interpretation than previous point charge models.

Contribution

It introduces an ab initio analysis method to determine rare earth valency in RIn3 and RSn3, improving upon outdated point charge models.

Findings

Eu and Yb are divalent in RIn3 and RSn3.

The ab initio calculations clarify the influence of valency on electric-field gradients.

A new scheme links electric-field gradients with chemical properties.

Abstract

In RIn3 and RSn3 the rare earth (R) is trivalent, except for Eu and Yb, which are divalent. This was experimentally determined in 1977 by perturbed angular correlation measurements of the electric-field gradient on a 111Cd impurity. At that time, the data were interpreted using a point charge model, which is now known to be unphysical and unreliable. This makes the valency determination potentially questionable. We revisit these data, and analyze them using ab initio calculations of the electric-field gradient. From these calculations, the physical mechanism that is responsible for the influence of the valency on the electric-field gradient is derived. A generally applicable scheme to interpret electric-field gradients is used, which in a transparent way correlates the size of the field gradient with chemical properties of the system.