Coexisting on- and off-center Yb3+ sites in Ce1-xYbxFe4P12 skutterudites

TL;DR

This study uses ESR measurements to reveal the coexistence of on-center and off-center Yb3+ sites in Ce1-xYbxFe4P12 skutterudites, providing insights into their distinct local environments and dynamics.

Contribution

It introduces Yb3+ ESR as a microscopic probe to distinguish and analyze different Yb3+ site occupations and their dynamic behaviors in skutterudite materials.

Findings

Two Yb3+ resonances with different temperature behaviors

Distinct hyperfine splittings indicating different rattling frequencies

Identification of low and high frequency Yb3+ site dynamics

Abstract

Electron Spin Resonance (ESR) measurements performed on the filled skutterudite system Ce1-x$YbxFe4P12 (x< 0.003) unequivocally reveal the coexistence of two Yb3+ resonances, associated with sites of considerably different occupations and temperature behaviors. Detailed analysis of the ESR data suggests a scenario where the fraction of oversized (Fe2P3)4 cages that host Yb ions are filled with a low occupation of on-center Yb3+ sites and a highly occupied T-dependent distribution of off-center Yb3+ sites. Analysis of the 171Yb3+ (I=1/2) isotope hyperfine splittings reveal that these two sites are associated with a low (~ 1 GHz) and a high (> 15 GHz) rattling frequency, respectively. Our findings introduce Yb3+ in Th symmetry systems and uses the Yb3+ ESR as a sensitive microscopic probe to investigate the Yb3+ ions dynamics.