Field and Pressure Tuning the Coupling of Crystal Electric Field and Phonon Modes in Praseodymium Sesquioxide*

The energetic overlap of phonons and low-lying crystal electric field (CEF) excitations in rare-earth sesquioxides is conducive to strong electron-phonon coupling and dramatic magnetostructural phenomena. For example, our previous temperature and magnetic field dependent Raman scattering studies on a member of this series, A-type Pr2O3, revealed significant phonon softening and a level repulsion between electronic and phononic levels. To explore these results further, we present a pressure-dependent Raman scattering study of Pr2O3 aimed at tuning the coupling between electron and phonon levels to modify the low temperature phase behavior. We observe that the degeneracy of the lowest lying CEF doublet is lifted under the application of pressure below 60 K and that the energy splitting increases linearly with increasing pressure or magnetic field. These results are indicative of a pressure-induced Structural Distortion that appears to be instigated by pressure-dependent electron phonon coupling. We discuss the possible effects of pressure on the magnetostructural properties of Pr2O3.