STUDIES ON STOICHIOMETRY AND IONIC-CONDUCTIVITY OF THE PYROCHLORE TYPE TL1+XTA1+XW1-XO6.NH2O SYSTEM

The system Tl1+xTa1+xW1-xO6. nH2O with 0 ≤x≤1 has been studied by means of TGA, X-ray diffraction and impedance measurements in the temperature region 300-700 K. The samples possess the cubic pyrochlore structure over the entire compositional and temperature range studied. At 575 K the conductivity σ = 1.4 × 10-2 (Ω cm)-1 for x = 0.80. The compositional dependence of the ionic conductivity at this temperature can be described by the equations {A figure is presented} and {A figure is presented} where a and b are the occupancy factors of the Tl+ ions at the crystallographic sites (16d) and (8b), respectively. At room temperature water is reversibly adsorbed. The content increases from n = 0.05 for x = 0 to n = 1.0 for x = 0.75 decreasing thereafter to 0.25 for x = 1. At 298 K the ionic conductivity of Tl1.75Ta1.75W0.25O6. nH2O increases from 5.5 × 10-8 (Ω cm)-1 to 4.1 × 10-5 (Ω cm)-1 as n increases from 0. to 1.0. © 1979.