Apatite-type silicates, RE10−x(SiO4)6O′

2+y (RE = La, Nd, Gd or Dy), were prepared

by mechanical milling, starting with stoichiometric mixtures of the constituent

oxides, RE2O3 and SiO2. X-ray diffraction patterns collected after grinding the

starting mixtures in a planetary ball mill for 9h contained only the characteristic

reflections of the target materials. The electrical properties were analyzed for

sintered pellets by using impedance spectroscopy, and the isothermal conductivity

data were successfully fitted to a Jonscher-type empirical expression σ’(ɷ) ∝ ωn;

with a decreasing fractional exponent, n, as the RE3+ cation-size increased. The

activation energies for oxygen migration were found to decrease, and the

conductivity increased, as the size of the RE3+ cation increased. The highest

conductivity values were obtained for the apatite-type lanthanum silicate. It was

also shown that the electrical properties of the as-prepared materials were

influenced by the silicon source used in their synthesis.

Ionic Conductivity of Apatite-Type Rare-Earth Silicates Prepared by Mechanical

Milling. L.G.Martínez-González, E.Rodríguez-Reyna, K.J.Moreno, J.I.Escalante-

García, A.F.Fuentes: Journal of Alloys and Compounds, 2009, 476[1-2], 710-4