MONOCLINIC SPIN-HAMILTONIAN ANALYSIS OF EPR-SPECTRA OF MN2-CRYSTALS( IN BIVO4 SINGLE)

X-band EPR spectra of Mn2+ in ferroelastic BiVO4 single crystals at ro om temperature taken in three orthogonal planes are analyzed using a t wo-stage least-squares fitting procedure. The absence of site splittin g from the spectra shows unequivocally that Mn2+ lies on a site with t wo-fold rotation symmetry, whose two fold axis is parallel to the mono clinic crystal axis. The low symmetry effects arising from the monocli nic site symmetry are evidenced by the observed coincidence of the ext rema for transitions between different Zeeman levels along the monocli nic axis, and by the 180 degrees rotational symmetry in the monoclinic plane and a small noncoincidence of the turning points in this plane. In the First stage, the spectra are fitted using the monoclinic form of the electronic Zeeman and fine structure terms (of second and fourt h degree) appropriate for the crystallographically de termined orienta tion of the monoclinic axis. In the second stage, fitting of the nucle ar hyperfine tensor (A) and the nuclear quadrupole tensor (P) is carri ed out with fixed values of the electronic Zeeman tensor (g) and fine structure terms, i.e. the tensor (D) and the fourth-degree terms, as o btained in the first stage. The principal axes of g, D, A, and P are f ound to be non-coincident in the monoclinic plane, as would be general ly expected for a monoclinic site.