Tysonite structure and crystal-field analysis of the Pr3+ ion in PrF3

The quadratic Zeeman effect of the Pr³⁺ ion in PrF₃ and a Raman spectroscopic investigation of the optical phonons in LaF₃ have been used to test the crystal structures proposed in the past for tysonite. We find that the twinned structure is consistent with all available experimental results. A crystal field Hamiltonian parametrized in monoclinic symmetry was used to describe the observed crystal field splittings of Pr³⁺ in PrF₃. Our best parameter set gave a r.m.s.-deviation of 12 cm^–1. As a test for the eigenfunctions the quadratic Zeeman shifts are calculated and compared with the experimental results.