Spin-Hamiltonian parameters and local structures of the tetragonal (CrO4)3− clusters in Cr5+-doped KDP-type crystals

• Spin-Hamiltonian parameters of Cr5+-doped KDP-type crystals are calculated.
• The calculation is based on the two (CF and CT)-mechanism model.
• The dynamic effect due to the vibrational motion of ligands is considered.
• Local structures of (CrO4)3− clusters in Cr5+-doped KDP-type crystals are obtained.

The spin-Hamiltonian parameters (g factors g//, g⊥ and hyperfine structure constants A//, A⊥) of tetragonal (CrO4)3− clusters in Cr5+-doped KDP-type crystals KH2PO4, KD2PO4, NH4H2PO4, ND4D2PO4, KH2AsO4, KD2AsO4 and NH4AsO4 are calculated from the high-order perturbation formulas based on the two-mechanism model for the elongated d1 tetrahedral clusters in crystals with the ground state |dx2-y2〉|dx2-y2〉. In the model, the contributions to spin-Hamiltonian parameters from both the crystal field (CF) mechanism and the charge-transfer (CT) mechanism (the latter is neglected in the widely-applied CF theory) are included. On the basis of the calculated values and by taking account of the small admixture of the first excited state |dz2〉|dz2〉 to the ground state |dx2-y2〉|dx2-y2〉 due to the vibrational motion of ligands (this dynamic effect leads a twinkling elongated tetrahedron to become a compressed one), all the calculated spin-Hamiltonian parameters are in reasonable agreement with the experimental values. The difficulty in the explanation of spin-Hamiltonian parameters by using the conventional static contributions for these Cr5+-doped KDP-type crystals are overcome, and the impurity-induced static local structures of (CrO4)3− clusters (which are different from the corresponding ones in the host crystals) in KDP-type crystals are estimated. The results are discussed.