J. Phys. Colloques
Volume 40, Numéro C2, Mars 1979International Conference on The Applications of The Mössbauer Effect
|Page(s)||C2-480 - C2-480|
J. Phys. Colloques 40 (1979) C2-480-C2-480
AN NGR OBSERVATION OF PROTON JUMPS IN TOURMALINEH. Pollak1, J. Danon2, R. Quartier1 and C. Dauwe1
1 Université National du Zaïre, Département de Physique, Groupe de l'Etat Solide, Campus de Kinshasa, Zaïre.
2 Centro Brasileiro de Pesquisas Fisicas, Rio de Janeiro, Brasil.
Une tourmaline ne contenant que des ions ferreux est étudiée par spectrométrie Mössbauer entre 4 K et 600 K. Le dédoublement des pics initiaux quand T croît est attribué à des sauts de protons dans le solide.
In Tourmaline the three M-sites share two by two a common edge, thus giving raise to a common oxygen ion (common point CP). Using symmetry considerations hydroxyl groups should be disposed as follows : a group at CP and three groups in the basic plane, such as to respect the trigonal configuration. Tourmaline commonly contains ferrous as well as ferric ions. The special investigated specimen only contains ferrous ones. With increasing temperature spectra, which at liquid helium display a quadrupole doublet, characteristic for a ferrous ion in octahedral symmetry, show shoulders on the inner sides of the doublet. As the temperature still increases, new lines appear with a much smaller quadrupole splitting but with quite the same isomeric shift. As their quadrupole splittings show a decrease from He 4 K to 600 K toward nearly one half the original value, they should be attributed to the same ferrous ions in a trans-octahedral site. A proton jumps could be the cause of the observed phenomen. As the CP proton is believed to stay fixed, it is normal that the temperature dependence of the quadrupole splitting is much faster than that of the pure electric field gradient. It looks like if there could be a proton jumps in solids, very similar to the one observed in chemical solutions. At very low temperature the relaxation mechanism is inhibited as proton rotations in hexamine /1/.