A study of the EPR spectrum of Fe3+ in diopside CaMg(SiO3)2 and spodumene LiAl(SiO3)2 has been made. It permits the calculation of all the constants of the spin Hamiltonian. We show that the pseudosymmetry axes of the fourth order tensor of the spin Hamiltonian are the same as the axes of the immediate environment of the Fe3+. From the fourth order constants of the spin Hamiltonian it is possible to obtain qualitative information about the Fe3+ environment. In both crystals, the Fe3+ is in the M 1 site. We show that the M 1 site is smaller and more distorted in spodumene than in diopside, and that in spodumene there is large tetragonal distortion along the M 1–01′ direction. It is seen that the information we obtain agrees very well with the crystallographic results.
Site-selective investigation of site symmetry and site occupation of iron in Fe-doped lithium niobate crystalsA new method of site assignment of Fe3+ in low symmetry crystals is presented. This method is based on the fact that the fourth order spin-Hamiltonian constants of Fe3+ are sensitive mainly to the immediate surroundings of the Fe3+. It is shown how it is possible to find the pseudosymmetry of the fourth order term of the spin Hamiltonian, while from the pseudosymmetry it is possible to define the orientation of the Fe-On complex in the structure and to localize Fe3+ in the crystal. To use this method the spin-Hamiltianian constants must be well known. The determination of the 20 constants of a general spin Hamiltonian is described. To apply our method in a low symmetry case, we studied Fe3+ in NaAJSiaOs, which has a triclinic lattice. Experiments were done on a single crystal at Q band frequency. The spin-Hamiltonian constants are given. It is shown that Fe 3 + is in a T1(0) site and substitutes for AJ3+.
La résonance paramagnétique électronique de l'ion Fe³⁺ dans les feldspaths a permis de confirmer le caractère ordonné ou désordonné de ces minéraux.
On a déterminé les constantes de l'hamiltonien de spin de l'ion Fe³⁺ dans les différents feldspaths et précisé la position des axes R. P. E.
Pour les feldspaths alcalins, on a montré que les ions Fe³⁺, ainsi que les ions Al³⁺, sont sur un seul site dans l'albite et le microcline maximum et sur les deux sites symétriques par rapport au plan (010) dans l'orthose et l'adulaire. Une expérience de diffusion a montré l'influence de la distribution des ions K⁺ et Na⁺ sur la résolution des spectres.
Dans la série des plagioclases, nous avons mis en évidence la structure péristérite de l'oligoclase, montré que le champ cristallin au niveau de l'ion Fe³⁺ est le même dans les cristaux de structure intermédiaire et dans la bytownite, et vu que l'anorthite est ordonnée.
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