Electrical Conductivity of TTF-Hydrogen Uranyl Phosphate Composite
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ELECTRICAL CONDUCTIVITY OF TTF-HYDROGEN URANYL PHOSPHATE COMPOSITE
L. MORENO-REAL", R.POZAS-TORMO*, S. BRUQUE* , M. MARTINEZ-LARA* AND J. RAMOS-BARRADO** "wDepartamentode Quimica Inorganica. Universidad de Malaga. "a$Departamento de Fisica Aplicada. Universidad de Malaga. Apartado 59, 29071 MALAGA. SPAIN.
ABSTRACT
H3 0U0 2P0 4 -.3H20 (HUP) undergoes intercalative reaction with tetrathiafulvalene (TTF) given a black solid with the next composition: (TTF)U0 2 P0 4.0.6H 20. The electrical conductivity fall from 2.40.10-6 n-1 cm-I (363K) to 8.8.10-8 n-1 cm-I (473K).
INTRODUCTION
Research on the synthesis of conducting polymers has recently attracted the interest of scientists. About this field, radical cation salts derived from tetrathiaand tetraselenafulvalenes (TTF and TSF) have been much more studied because some of them have found to exhibit superconductivity at low temperatures Ifl. TTF and derivatives are electron-donor molecules and are easily oxidized to the stable radical cation and the dication. These organic molecules are involved in highly conducting charge transfer compounds and they can form superconductors. The high conductivity is anisotropic and associated with crystal structures in which the donor and acceptor molecules, as in TTF-TCNQ, form segregated stacks with extensive ft-electron overlap and delocalization along these one-dimensional stacks. Some discreet inorganic anions have been used as electron n-aceptor : halides, C1O4- , ReO4- , PF6 ,AsF6-,...etc. 12], resulting materials with high conductivity and/or superconductivity at low temperature. Lamellar solids have also being employed as macroanionic electron t-aceptor: iron oxychloride 13,4,51, layered silicates 161 and V2 05 xerogels 17,81. The aim of this work is the preparation of a new composite material by intercalation of TTF into the lamellar uranyl phosphate host (H3 0U0 2 PO4 .3H 2 0, HUP). This solid has a high acidity and is a fast protonic conductor. The exchange and acid-base reactions have ben extensively studied [9]. Our purpose in this contribution will be to determine the structural features of TTF intercalated in HUP and its electrical conductivity.
Mat. Res. Soc. Symp. Proc. Vol. 210. (1991
Materials Research Society
444
EXPERI MENTAL
The intercalate was prepared by treating HUP at 60'C with solution of tetrathiafulvalene in absolute methanol (TTF/U 4:1). The resulting black solid was filtered, washed using the same solvent and dried in air. The new material was characterized by chemical analysis, infrared spectroscopy (Perkin-Elmer 883), x-ray diffraction (Siemens D-501), differential thermal and thermogravimetric analysis (Rigaku Thermoflex). For the electrical measurements, pellets, 13 mm in diameter and I mm thick, were prepared by pressing the powder at 6 MPa. Opposite faces of disc-shaped samples were coated with gold by a vapour deposition method. The ac electrical impedance of the pellet was performed using a frequency response analyser Solartron FRA 1255 and a electrochemical interface Solartron 1286 which
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