4f-2p hybridization driven electronic structure of tetravalent praseodymium in ternary chalcogenides*

Tetravalent praseodymium (Pr⁴⁺) with 4f¹ electron configuration is isoelectronic to Ce³⁺. However, crystal electric field (CEF) measurements on Pr⁴⁺ in different systems indicate the first CEF level is ~230 meV, the largest that has been observed for a lanthanide ion.¹ This brings about the need for an intermediate coupling scheme owing to the comparable energy scales of spin-orbit coupling (SOC) and CEF. In this talk, I will present out work on a series of Pr⁴⁺ systems showing evidence of increased metal-ligand covalency compared to the traditional trivalent lanthanides. A combination of X-ray (L₃-edge XANES, M_4,5-edge XANES/XMCD, O K-edge XANES/XMCD), optical (FIRMS), and neutron (INS) spectroscopies, will be utilized to understand the single-ion properties, exchange interactions and bulk behavior driven by covalency and increased CEF in tetravalent praseodymium. Where appropriate, these analyses will be supported by comparisons to our studies of redox chemistry and electronic structure in mixed valence Pr^3+/4+ ternary chalcogenide systems.