J. Phys. IV France 113 (2004) 115
Étude des propriétés de conduction électrique des phosphates condensés mixtes éléments monovalents-terres rares : LiDy(PO 3) 4, NaNd(PO 3) 4, AgLa(PO 3) 4, NH 4DyPO 3) 4M. Férid1, K. Horchani1, A. Touai2, A. Madani2, H. Boussetta2 and M. Trabetsi-Ayedi3
1 Laboratoire des Procédés Chimiques, Institut National de Recherche Scientifique et Technique, BP. 95, 2050 Hammam-Lif, Tunisie
2 Laboratoire de Physique des Matériaux, Faculté des Sciences de Bizerte, 7021 Zarzouna, Tunisie
3 Laboratoire de Physique-Chimie Minérale, Faculté des Sciences de Bizerte, 7021 Zarzouna, Tunisie
Single crystals of LiDy(PO 3) 4, NaNd(PO 3) 4, NH 4Dy(PO 3) 4 and AgLa(PO 3) 4 polyphosphates have been grown using the flux method. A mixture of monovalent carbonate (M 2CO 3), rare earth oxide (Ln 2O 3) and phosphoric acid (H 3PO 4 85%) was heated at 285°C during a week. Single crystals were obtained and characterized by X-ray diffraction, infrared and Raman spectroscopy. Their investigation was carried out by thermal analysis (ATG/ATD). Their electric conductivity was measured by impedance spectroscopy. The conductivity, , vary between .cm -1 at 300 °C and .cm -1 at 500 °C. The activation energies increase from 0,31 for NH 4Dy(PO 3) 4 to 1,26 eV for NaNd(PO 3) 4. The basic structural units of these phosphates are ribbons (PO 3) formed by corner-sharing of PO 4 tetrahedra with variable geometry, which are unfavourable to the ionic conduction. The ionic transport was mainly assured by M + ions; moreover, the hydrogen bond established in the structure of NH 4Dy(PO 3) 4 and the proton exchange allow to explain the relatively high conductivity of this phosphate. The results are discussed and correlated to the structural properties of these phosphates.
© EDP Sciences 2004