Dopant Fe 3 t ions in tetrahedral and octahedral positions of Ge 4 I in the crystal Li,GePI5 were studied using EPR. Fe H substitutes for Gc 4 + with a local charge compensation. The octahedral site and the tetrahedral sites significantly differ by the value of the invariant sum S(B 4 ) of the B 4 tensor of the spin Hamiltonian of Fe H . The irreducible tensor products {V 4®V4 } 4 and {V 4®V4 } , of the V 4 tensor of the crystal field calculated using the point-charge model for octahedral and tetrahedral complexes provide the predominant contribution of the crystal field to the B 4 and B, tensors of the spin Hamiltonian of Fe H , respectively. A comparison of the fourth-rank tensors B 4 of the spin Hamiltonian and {V 4 ® V 4 } 4 of the crystal field determined at 300 K with those determined at 77 K supports the conclusion that the phase transition is accompanied by combined rotations of the [Ge0 41 tetrahedra with the [Ge(l)061 octahedron almost unaltered. The spectrum lines are narrow and the variety of point defects in the vicinity of the paramagnetic impurity ions Fe H , Cr 3 + and Cu" is not detected. These facts are inconsistent with the statistically distributed model for the Li(2) atom. In specific cases at 300 K, when the wings of the two spectrum lines of the M -M+ I and the M+ 2 -M+ 3 transitions of Fe H ions belonging to one system of translationally equivalent positions overlap an extra line appears in the center between these lines. It is suggested that this effect is due to the soft phonon mode above the phase transition temperature.
An electron paramagnetic resonance study of a synthetic single crystal of
Cr-doped LiScGeO4 was carried out at the X- and Q-bands at 300 K
and at the broad band (70-370 GHz) at 4.2 K. It was established that the
EPR spectra with the magnetic multiplicity KM = 2 observed in all the
frequency bands are due to the Cr3+ substituted for Sc3+ at the mirror symmetry octahedral site. The angular dependences
of the two symmetry-related spectra of Cr3+ in the three
crystallographic planes were fitted with the spin Hamiltonian (S = 3/2) of
monoclinic symmetry. The zero-field splitting of the ground state energy
levels was determined as 1.309(5) cm-1 which compares well with
that for Cr3+ in forsterite and alexandrite crystals with
similar olivine-like structure. Additional weak lines due to Mn2+ and Fe3+ at the mirror symmetry sites were also
identified in the X- and Q-band spectra.
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