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The electron spin resonance (ESR) spectra of SO 3 − and SO 2 − radical ions with a linewidth ΔH ≈ 2.7 G and SO 3 − (A 1) and SO 3 − (A 2) centers with superhyperfine splitting due to the interaction with protons in platelike gypsum single crystals under X-ray irradiation have been analyzed at 25°C. Dehydrated regions with a radius >4 A are revealed in gypsum. The ESR spectra of SO 3 − radical ions and atomic hydrogen with ΔH ≈ 0.3 G are found in the products of isothermal annealing of gypsum kept for 30 min after X-ray irradiation at 25°C. The dependences of the intensities of these spectra on the annealing temperature are studied in the range of 100–450°C. The temperature range of formation of α- and β-phase states of bassanite and γ-anhydrite are determined. The process of residual water redistribution between the channel systems of the α- and β-phase types of γ-CaSO4 in gypsum thermal derivatives is established.

The conditions for equivalent positions on the (hkl) face of growing crystal are derived using symmetry elements of the space group. It is shown by the example of the sp. gr. D2h16 that the conditions of equivalent position formation coincide with conditions of the reflection of diffracted beams by crystal. It is established that electron spin resonance (ESR) centers in barite, SO4− (I) and SO4− (II), with only two conjugate spectra with equal intensity out of four, and SO4− (III), with a different intensity of conjugate spectra KαM = 2, are localized into the growth pyramid of the (001) face with a [010] step. SO2−, SO3−,, and SO4− (IV) centers, having an identical intensity of the conjugate ESR spectra with KαM = 2, are localized into the growth pyramid of the (210) face with a growth step [001].

The EPR spectra of Fe3+ impurity ions in NaZr2(PO4)3 single crystals at 300 K are investigated, and the spin Hamiltonian of these ions is determined. A comparative analysis of the spin-Hamiltonian and crystal-field tensors is performed using the maximum invariant component method. It is demonstrated that Fe3+ impurity ions substitute for Zr4+ ions with local compensator ions located in cavities of the B type. It is revealed that the invariant of the spin-Hamiltonian tensor B 4 and the crystal-field tensor V 4 44 depend substantially on the mutual arrangement of ions in the first and second coordination spheres. The corresponding dependences are analyzed.

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.

A single crystal of doped with was studied by EPR at room temperature and at using an X-band spectrometer. There are two magnetically equivalent spectra characterized by the main Stevens constants and . The spectra are described by a general spin Hamiltonian and all constants have been determined. The zero-field splitting of the energy levels is of the order of and EPR lines exist at very low fields, which are identified. The spectra are temperature dependent. This is interpreted as an anisotropic modification of the environment. The analysis of the pseudo-symmetry of the fourth order term of the spin Hamiltonian shows a strong modification of the local structure. The coordination polyhedra of are different from Zn and K polyhedra. The comparison with other results from the double sulphate family is made.

In single crystal colquiriite LiCaAlF6 doped with Gd3+ ions two EPR spectra of the Gd3+ ions with the Laue site-symmetry groups Ci and C3i were observed. The spectrum angular dependence for trigonal Gd3+ centre was investigated in detail and corresponding spin Hamiltonian parameters were fitted. From analysis of the spin Hamiltonian tensorsB 4 andB 6 it was established that Gd3+ with the Laue group C3i substitutes at Ca2+ site with the excess charge compensation by an ion located along the threefold axis from this site. The transformation formulas for a sixth-rank irreducible Hermitian tensor under coordinate rotation are tabulated in an explicit form. By using the EPR data for Gd3+ substituted in a variety of host crystals, the fourth-rank and sixth-rank tensors of Gd3+ spin Hamiltonians were tabulated and correlated with structures of the coordination polyhedra at substitution sites. The results suppose a predominance of quadratic crystal field contributions into the spin Hamiltonian tensorB 4 of Gd3+.

Dopant Fe3+ ions in tetrahedral and octahedral positions of Ge4+ in the crystal Li2Ge7O15 were studied using EPR. Fe3+ substitutes for Ge4+ with a local charge compensation. The octahedral site and the tetrahedral sites significantly differ by the value of the invariant sumS(B 4) of theB 4 tensor of the spin Hamiltonian of Fe3+. The irreducible tensor products {V 4 ⊗ V 4}4 and {V 4⊗V 4}2 theV 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 theB 4 andB 2 tensors of the spin Hamiltonian of Fe3+, respectively. A comparison of the fourth-rank tensorsB 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 rotation of the [GeO4] tetrahedra with the [Ge(1)O6] octahedron almost unaltered. The spectrum lines are narrow and the variety of point defects in the vicinity of the paramagnetic impurity ions Fe3+, Cr3+ and Cu2+ 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 theM→M+1 and theM+2 →M+3 transitions of Fe3+ 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.

The expansion of the {B2} and {B4} tensors of the spin Hamiltonian (SH) for Mn2+ (6S-state) is performed in terms of the irreducible tensor products {VL1 ⊗VL2}2 and {VL1 ⊗VL2}4 of the crystal field (CF) tensors {VL1} and {VL2}. The EPR spectra of Mn2+ in the ZnSeO4·6H2O crystal are studied and the SH tensors {B2} and {B4} are calculated. The tensors {V4⊗V4}2 and {V4⊗V4}4 are computed using the point-charge model (PCM) of the [Zn(H2O)6] complex with the C2 symmetry and are compared with the SH tensors {B2} and {B4}, respectively. The correct signs of the elements and the pseudo-symmety axes of the tensors are obtained both for the {B2} tensor and {V4⊗V4}2 and for the {B4} tensor and {V4⊗V4}4. It is concluded that the irreducible tensor products {V4⊗V4}2 and {V4⊗V4}4 provide the predominant contribution respectively to the SH tensors {B2} and {B4} of Mn2+.

The orientational dependences of the EPR spectra of Fe3+-doped LiCaAlF6 single crystals (space group P31c, Z=2), grown at the Laboratory of Magnetic Radio Spectroscopy at Kazan’ State University, have been investigated in detail. The spectrum is described by a trigonal spin Hamiltonian with the following parameters: B 20=40.072×10−4 cm−1, B 40=−5.799×10−4 cm−1, B 43=−4.281×10−4 cm−1, A s=24.33±1, A p=6.13±1, g ∥=g ⊥=2.00217±0.0003. A theoretical calculation of the hyperfine structure parameters shows that they are described quite well when allowance is made for the overlapping of the wave functions of the paramagnetic center and the ligands (F−).

The results of our research on travertine-like barite by electron paramagnetic resonance (EPR) are presented. The growth of these crystals was held in continuous motion of gas-water solutions at a constant radiation exposure of the nuclei 226 Ra, 232 Th and 40 K. The objective of this work was to identify the crystal-structure features of travertine-like barite associated with growth conditions under the influence of radiation exposure. Radiographic studies of barite samples have shown that the aggregates are virtually mono-mineral formations. It has a compressed unit cell with lower volume and higher density compared to the parameters of sedimentary barites. Only weak lines of the EPR spectrum of the ion-radical SO 2 − were fixed in the natural sample of barite. Therefore, laboratory experiments were carried out with X-ray ionization of samples, not only of the original rock, but also of samples exposed to thermal annealing. The EPR spectra of the following ion radicals: О − (g xx =2.0186; g yy =2.0121; g zz =2.0093), SO 2 − (g xx =2.0033; g yy =2.0126; g zz =2.0105) and two type - SO 3 − (I) (g xx =2.0034; g yy =2.0024; g zz =1.9995), SO 3 - (II) (g xx =2.0076; g yy =2.0022; g zz =1.9979) were detected after X-ray irradiation. The intensities of the lines of the observed EPR spectra of ion radicals change with annealing temperature. Paramagnetic centres form an integrated system with the structure of the crystal. Within the system, the transfer of electrons and holes is observed.