ENDOR Investigation of Cr³⁺ Centres in the Tetragonal Phase of RbCdF₃

Cr 3+ centres in the perovskite RbCdF 2 are studied with ENDOR at 17 K. The spin‐Hamiltonian parameters obtained for 53 Cr and the first, second, and third nearest set of 19 F neighbours show the influence of the structural phase transition from the cubic to tetragonal phase at T c = 124 K. The results indicate that the influence of the lattice relaxation around the impurity ion is seen even in the third shell of 19 F neighbours, which limits the use of Cr 3+ as a probe to study the structural phase transition.