Anelastic spectroscopy study of the metal-insulator transition of Nd(1-x)EuxNiO3

TL;DR

This study investigates the elastic properties of NdNiO3 and Nd0.65Eu0.35NiO3 across the metal-insulator transition, revealing a stiffening linked to the disappearance of Jahn-Teller distortions, independent of magnetic ordering.

Contribution

It provides new insights into the elastic anomalies and Jahn-Teller distortions associated with the metal-insulator transition in RNiO3 compounds, highlighting the role of structural changes.

Findings

Narrow dip in Young's modulus at MIT

Abrupt stiffening of ~6% during cooling

Jahn-Teller distortions disappear at MIT

Abstract

Measurements are presented of the complex dynamic Young's modulus of NdNiO3 and Nd0.65Eu0.35NiO3 through the Metal-Insulator Transition (MIT). On cooling, the modulus presents a narrow dip at the MIT followed by an abrupt stiffening of ~6%. The anomaly is reproducible between cooling and heating in Nd0:65Eu0:35NiO3 but only appears as a slow stiffening during cooling in undoped NdNiO3, conformingly with the fact that the MIT in RNiO3 changes from strongly first order to second order when the mean R size is decreased. The elastic anomaly seems not to be associated with the antiferromagnetic transition, which is distinct from the MIT in Nd0.65Eu0.35NiO3. It is concluded that the steplike stiffening is due to the disappearance or freezing of dynamic Jahn- Teller (JT) distortions through the MIT, where the JT active Ni3+ is disproportionated into alternating Ni3+d and Ni3-d. The fluctuating octahedral JT distortion necessary to justify the observed jump in the elastic modulus is estimated as ~3%, but does not have a role in determining the MIT, since the otherwise expected precursor softening is not observed.