Physics of Polymorphic Transitions in CeRuSn

TL;DR

This study investigates the polymorphic transitions in CeRuSn, revealing successive structural changes with significant volume collapse linked to Ce site inequivalence and bond ratio changes, influenced by Kondo physics and lattice vibrations.

Contribution

It provides detailed experimental insights into the structural and physical changes during polymorphic transitions in CeRuSn, highlighting the role of Ce site inequivalence and bond ratios.

Findings

Successive structural transitions at 290 K and 225 K.

Significant volume collapse along the c axis.

Transitions influenced by Kondo physics and lattice vibrations.

Abstract

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of X-ray diffraction experiments conducted at 300, 275 and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present X-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (290 K) and than to a triple CeCoAl superstructure at 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the transition in elementary Cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations might be the driving forces.