Cooperative Jahn-Teller Distortion in PrO2

TL;DR

This paper reports the discovery of a cooperative Jahn-Teller distortion in PrO2 at 120 K, affecting its crystal and magnetic structure, with detailed measurements of its physical properties and discussion of underlying mechanisms.

Contribution

It provides the first neutron diffraction evidence of a cooperative Jahn-Teller distortion in PrO2 and analyzes its structural, magnetic, and electronic implications.

Findings

Jahn-Teller distortion occurs at 120 K in PrO2.

The unit cell doubles along one axis below TD.

Electrical conductivity shows activated behavior with Ea = 0.262 eV.

Abstract

We report neutron diffraction data on single crystal PrO2 which reveal a cooperative Jahn-Teller distortion at TD = 120 +/- 2 K. Below this temperature an internal distortion of the oxygen sublattice causes the unit cell of the crystallographic structure to become doubled along one crystal axis. We discuss several possible models for this structure. The antiferromagnetic structure below TN = 13.5 K is found to consist of two components, one of which shares the same doubled unit cell as the distorted crystallographic structure. We also present measurements of the magnetic susceptibility, the specific heat capacity and the electrical conductivity of PrO2. The susceptibility data show an anomaly at a temperature close to TD. From the specific heat capacity data we deduce that the ground state is doubly degenerate, consistent with a distortion of the cubic local symmetry. We discuss possible mechanisms for this. The conductivity shows an activated behaviour with an activation energy Ea = 0.262 +/- 0.003 eV.