Anomalous high-pressure Jahn-Teller behavior in CuWO4

TL;DR

This study investigates the persistence and behavior of Jahn-Teller distortion in CuWO4 under high pressure, revealing its persistence up to 37 GPa and its role in phase transition mechanisms.

Contribution

It provides the first experimental evidence of Jahn-Teller distortion persisting at high pressures in CuWO4 and analyzes its influence on phase transitions.

Findings

Jahn-Teller distortion persists up to 37 GPa.

Distortion decreases with pressure but increases sharply at phase transition.

Pressure-induced phase transition reduces distortive effects.

Abstract

High-pressure optical-absorption measurements performed in CuWO4 up to 20 GPa provide experimental evidence of the persistence of the Jahn-Teller (JT) distortion in the whole pressure range both in the low-pressure triclinic and in the highpressure monoclinic phase. The electron-lattice coupling associated with the eg(Exe) and t2g(Txe) orbitals of Cu2+ in CuWO4 are obtained from correlations between the JT distortion of the CuO6 octahedron and the associated structure of Cu2+ d-electronic levels. This distortion and its associated JT energy (EJT) decrease upon compression in both phases. However, both the distortion and associated EJT increase sharply at the phase transition pressure (PT = 9.9 GPa) and we estimate that the JT distortion persists for a wide pressure range not being suppressed up to 37 GPa. These results shed light on the transition mechanism of multiferroic CuWO4 suggesting that the pressureinduced structural phase transition is a way to minimize the distortive effects associated with the toughness of the JT distortion.